essay on satellites

Essay on Satellite

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100 Words Essay on Satellite

Introduction to satellites.

Satellites are objects in space that orbit around larger bodies, like Earth. They can be natural, like moons, or man-made for various purposes.

Types of Satellites

There are many types of satellites. Communication satellites help in sending signals for television and phones. Weather satellites help predict weather changes. Navigation satellites assist in GPS systems.

Importance of Satellites

Satellites are important as they help us in communication, weather forecasting, navigation, and scientific research. They play a crucial role in our daily lives and scientific advancements.

Understanding satellites is fascinating. They are a testament to human ingenuity and our quest to explore the universe.

250 Words Essay on Satellite

Introduction, the science behind satellites.

Satellites operate on the principle of gravity. Launched into space by rockets, they maintain their orbit around planets due to the balance between their forward motion and the gravitational pull of the planet. The height and speed of the satellite determine the nature of its orbit.

Satellites are broadly classified into natural and artificial. Natural satellites are celestial bodies that orbit a planet, like the moon. Artificial satellites, on the other hand, are man-made and serve specific purposes. They can be further divided into categories like communication, weather, navigation, and research satellites.

Applications of Satellites

Satellites have revolutionized our lives. Communication satellites enable global connectivity, facilitating television broadcasts, phone calls, and internet services. Weather satellites provide meteorological data, aiding in weather prediction and climate studies. Navigation satellites like GPS ensure accurate location and timing information. Research satellites contribute to space exploration and scientific discoveries.

In conclusion, satellites have become an indispensable part of our lives. They have not only advanced our understanding of the cosmos but also enhanced our capabilities in communication and navigation. As technology progresses, the potential applications of satellites are bound to increase, paving the way for a future where space technology is even more ingrained in our daily lives.

500 Words Essay on Satellite

Satellites, the celestial bodies orbiting around a planet, have become an integral part of our modern life. They are not only vital for scientific exploration but also for communication, weather monitoring, navigation, and numerous other applications. This essay aims to delve into the world of satellites, their types, uses, and significance.

Understanding Satellites

Satellites can be broadly classified into two categories: natural and artificial. Natural satellites are celestial bodies like moons, while artificial satellites are human-made machines launched into space for specific tasks. Artificial satellites can be further categorized into communication satellites, weather satellites, navigation satellites, reconnaissance satellites, and scientific satellites, among others.

Satellites play a pivotal role in various aspects of our daily lives. Communication satellites have revolutionized global communication by facilitating television broadcasts, telephone calls, and internet services. Weather satellites help predict weather changes, enabling timely disaster warnings and facilitating agricultural planning. Navigation satellites, like those in the GPS system, provide precise positional data for navigation on land, sea, and air. Scientific satellites aid in astronomical observations and earth science studies, providing valuable data about our universe and our planet.

Challenges and Future Prospects

Furthermore, the increasing dependence on satellites raises concerns about cybersecurity. As these satellites transmit sensitive data, they become potential targets for cyber-attacks.

Looking ahead, the future of satellites is promising. Developments in technology are paving the way for smaller, more capable satellites. The concept of satellite constellations, a group of satellites working together, is gaining traction. Companies like SpaceX with its Starlink project aim to provide global broadband coverage using these constellations.

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What Is a Satellite?

What do you think of when you hear the word “satellite”? Maybe you think of a big metal spacecraft that circles our planet in space.

When we think of satellites, we usually think of something that looks like this. Image credit: Maxar Technologies

But, did you know that our Earth and Moon are satellites, too? A satellite can be any object that orbits a planet, star, or moon. An orbit is a regular, repeating path that one object in space takes around another one. So, Earth is a satellite, because it orbits the Sun ! The Moon is also a satellite because it orbits Earth. But, usually, the word "satellite" refers to a machine that is launched into space and moves around Earth or another body in space.

Earth and the Moon are examples of natural satellites. Thousands of artificial, or man-made, satellites orbit Earth. Some take pictures of the planet that help meteorologists predict weather and track hurricanes. Some take pictures of other planets, the Sun, black holes , dark matter or faraway galaxies . These pictures help scientists better understand the solar system and universe.

Believe it or not, there are satellite galaxies, too! Learn all about them here !

This illustration shows NASA's Earth-observing satellite fleet. Image credit: Jenny Mottar/NASA

Other satellites are used for communications, such as TV signals and phone calls around the world. Have you ever tried to find your house, or the closest ice cream shop, on a map on your phone? Satellites help us do this with GPS! A group of more than 20 satellites make up the Global Positioning System , or GPS. These satellites can help figure out your exact location.

Why are satellites important?

The view that satellites like GPS have allows them to see large areas of Earth at one time. This means satellites can collect more data, more quickly, than instruments on the ground.

Satellites also can see into space better than telescopes at Earth's surface! That's because satellites fly above the clouds, dust, and molecules in the atmosphere that can block the view from the ground.

Clouds can block the view of space from the ground. Satellites fly high above the clouds, helping us see the universe better. Image credit: Pixabay/Pexels

What are the parts of an artificial satellite?

Man-made satellites come in many shapes and sizes. But most have at least two parts in common - an antenna and a power source. The antenna sends and receives information, usually to and from Earth. Just like a toy that requires batteries to work here on Earth, satellites need power, too! There are several types of power sources for satellites, such as solar panels or batteries. Solar panels are cool because they power the satellite by turning sunlight into electricity.

Satellites can have solar panels as power sources. Image credit: Pixabay/Pexels

Many NASA satellites carry cameras and scientific sensors. Sometimes, these instruments point toward Earth to gather information about its land, air and water. Other times, they face toward space to collect data from the solar system and universe.

How do satellites orbit Earth?

Most satellites are launched into space on rockets . A satellite orbits Earth when its speed is balanced by the pull of Earth's gravity. Without this balance, the satellite would fly in a straight line off into space or fall back to Earth.

Satellites orbit Earth at different heights, different speeds and along different paths. The two most common types of orbit are "geostationary" (jee-oh-STAY-shun-air-ee) and "polar."

A geostationary satellite travels from west to east over the equator. It moves in the same direction and at the same rate Earth is spinning. From Earth, a geostationary satellite looks like it is standing still since it is always above the same location.

From Earth, a geostationary satellite looks like it is always in the same place, because it moves in the same direction and at the same rate the Earth spins. Image credit: NASA Solar System Exploration

Polar-orbiting satellites travel in a north-south direction from pole to pole. As Earth spins underneath, these satellites can scan the entire globe, one strip at a time.

Why don't satellites crash into each other?

Actually, they can! In February 2009, two communications satellites – one American and one Russian – crashed in space! This, however, is believed to be the first time two man-made satellites have collided accidentally.

But, don’t worry! NASA and other organizations across the world keep track of satellites in space. Collisions usually don’t happen because when a satellite is launched, it is placed into an orbit designed to avoid other satellites. But orbits can change over time, and the chances of a crash increase as more and more satellites are launched into space.

What is the history of NASA satellites?

NASA has launched dozens of satellites into space, starting with the Explorer 1 satellite in 1958. Explorer 1 was America's first man-made satellite. The main instrument aboard was a sensor that measured high-energy particles in space called cosmic rays.

The first satellite picture of Earth came from NASA's Explorer 6 in 1959. TIROS-1 followed in 1960 with the first TV picture of Earth from space. These pictures did not show much detail. But they did show the potential satellites had to change how people view Earth and space.

How it started… This is the first-ever satellite image of Earth, captured by Explorer 6 on August 14, 1959. It looks just like a blur – but it showed the potential satellites had to change how people could view Earth from space. Satellites have become much better at taking pictures since then! Image credit: NASA Kennedy Center

How does NASA use satellites today?

NASA satellites help scientists study Earth, the other worlds of our solar system, and beyond.

Satellites looking toward Earth provide information about clouds, oceans, land and ice. They measure gases in the atmosphere , such as carbon dioxide. NASA's Orbiting Carbon Observatory 2 , or OCO-2, launched in 2014 to measure carbon dioxide levels on Earth to better observe Earth's carbon cycle. NASA's OCO-2 also helps explore how measurements from space can predict future CO2 increases and its impact on Earth's climate.

Satellites also measure the amount of energy that Earth keeps inside the atmosphere, and the amount of energy the Earth sends back into space. And satellites monitor wildfires and volcanoes and their smoke.

An illustration of OCO-2, a satellite that studies carbon dioxide, taking carbon dioxide measurements on Earth all the way from space. Image credit: NASA/JPL-Caltech

All this information helps scientists predict weather and climate. The information also helps public health officials track disease and famine; it helps farmers know what crops to plant; and it helps emergency workers respond to natural disasters. Did you check the weather forecast today? We know today’s weather thanks to satellites!

Satellites that face toward space have many jobs. Some watch for dangerous rays coming from the Sun. Others explore asteroids and comets, the history of stars, and the origin of planets. Some satellites fly near or orbit other planets. These spacecraft may look for evidence of water on Mars or capture close-up pictures of Saturn's rings.

Build a NASA spacecraft at home!

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Satellite Technology: Past, Present, and Future

Since the first satellite was launched into orbit in 1957, space technology has evolved drastically. Satellites were once as big as a small school bus and weighed up to 6 tons. The situation has changed over the last decade with the development of small standardized satellites and reusable launch capabilities driving the growth of new space-based infrastructure. Today, thousands of satellites of all types orbit around the Earth, enabling a wide variety of communications, positioning, and earth observation applications. 

Communications satellites have enabled us to have in-flight telecommunications, high-speed networks in rural areas, cable TV and network programming; Positioning satellites have powered us with the convenience of location-based services, allowed us to understand where we are and track movements anywhere on the planet; Earth observation satellites provided an ability to count, measure, and detect change across industries including agriculture, energy, mining, and urban planning, to name a few. These unique satellite technology capabilities helped create a globalized and connected planet that drives our modern economies and helps each of us manage our daily lives.

Satellite Technology Provides Ubiquitous Connectivity

Have you ever wondered how you are able to use the internet on the plane? Satellites provide the only truly global infrastructure, which makes it possible to connect cars, ships, and even planes to the internet. ViaSat is a broadband satellite communications provider that brings in-flight Wi-Fi to full-service, regional, and low-cost carriers. The company is nearing deployment of a new generation of high-capacity Viasat-3 Ka-band satellites that will expand its network capacity and coverage. The first satellite, Viasat-3A, covering the Americas and portions of the Atlantic and Pacific oceans, is scheduled to launch in the first quarter of 2022. This means in the near future, when you board a long flight, thanks to satellite technology, you will have access to the internet with much lower latency allowing you to use all the applications you need, whether it’s accessing popular streaming services such as Netflix, hosting a video conference, or even playing your favorite online games.

Have you ever gone to a national park and lost your cell phone service? If so, would you want a portable device that can receive internet anywhere in the world? SpaceX has set out to do just that. Led by Elon Musk, the company started Starlink in 2015 to develop high-performance satellites and customer terminals that deliver broad access to space-based Internet. SpaceX plans to deploy up to 40,000 Starlink satellites and has launched over 1,600 at the end of 2021. Traditional geostationary satellites orbit 22,000 miles away from the Earth, while SpaceX's mega-constellation of satellites will maintain orbit at only 350 miles. This means that Starlink’s signals don't have to travel nearly as far and therefore speeds and reliability are expected to be more stable over time as the constellation grows and satellite technology improves. 

SpaceX started a private beta service in the Northern United States in August 2020 and a public beta in October 2021. The beta demonstrated that some users could reach download speeds of more than 210 megabits per second (Mbps) — faster than 95% of US connections, according to the speed-test provider Ookla 1. SpaceX is preparing for commercial launch in 2022 and expected to boost production of both satellites and user terminals. Elon Musk has been promising that Starlink’s speeds will continue to increase and could reach 300 Mb/s later this year. In addition, the latency for Starlink is expected to drop to 20 milliseconds or lower, making the service capable of delivering a modern internet experience including streaming, collaboration, and gaming. Current Starlink terminals offer coverage over the entire United States, but the company plans to expand globally. 

Satellite Technology Allows for Precise Positioning & Navigation

In 1978, the original NAVSTAR satellite was launched and it gave the U.S. government the first reference point for a worldwide radio-navigation system that later became the GPS (Global Positioning System) we know and love. GPS has transformed our lives in many ways and fundamentally changed our spatial awareness. But it took nearly three decades and numerous companies to achieve the widespread adoption we know today.  One early pioneer was Charles Trimble started Trimble Navigation (later known as Trimble) the same year the first NAVSTAR satellite was launched. Although GPS was developed exclusively to meet military needs, Trimble foresaw a wide range of commercial and business applications for a system that could pinpoint location anywhere on the planet. The company’s decision to fully embrace the emerging NAVSTAR system has proven to be a brilliant one and positioned Trimble at the forefront of satellite-based position technology. Today, Trimble’s technology in positioning, modeling, connectivity, and geospatial data analytics has helped enable industries such as agriculture, transportation, civil construction, and telecommunications, allowing consumers to have more choices of food at supermarkets, getting our parcels delivered faster and experiencing skyscrapers rising up in the city.

Learn more: The GPS Playbook

Another decades-old company that contributed heavily to the development of GPS is Inmarsat . Founded in 1979, Inmarsat has over 40 years of experience enhancing the accuracy and dependability of GPS data for safety-related users such as aircraft and ships. They call this concept the Satellite Based Augmentation System (SBAS). The company worked closely with the European Space Agency (ESA) on developing the first prototype of SBAS in 1989 and launched the Inmarsat-3 constellation 1 year after that featured navigation transponders on all spacecraft for SBAS services. Today, the powerful benefits SBAS is able to provide are accuracy and integrity that are critical to aviation and the geospatial industry. Inmarsat is working to modernize air traffic management using SBAS and to alleviate airspace congestion so we can experience shorter flight times, fewer unexpected delays, and maintain confidence in the safety and security of air travel.

Satellite Technology Permits Unprecedented Understanding

Earth Observation data helps us see changes on a planetary scale and the insights that businesses, governments, researchers and journalists derive from the imagery drive economic activity and improve the quality of our lives. These types of satellites make it possible to count, measure, and quantify the world around us as never before, enabling near real-time monitoring anywhere on Earth. Planet Labs has the world’s largest imaging constellation with 200 satellites providing the highest frequency of imaging capabilities commercially available - up to 12 times per day. The company’s monitoring capabilities create significant value for businesses while also supporting global humanitarian and sustainability efforts. They have helped global companies to transition into green businesses by standardizing reporting metrics and verifying sustainable practices, agriculture businesses manage food production to eliminate food waste, governments to plan for wildfire mitigations, and journalists to battle human rights abuses by uncovering illegal shipping and forceful detention.

Global energy-related carbon dioxide emissions are on course to rise by 1.5 billion tonnes in 2021, which is the second-largest increase in history. Greenhouse gases have far-ranging environmental and health effects - they cause climate change by trapping heat, which then cause extreme weather, food supply disruptions, increased wildfire and other effects, and they also contribute to respiratory disease from smog and air pollution. GHGSat provides broad-based emissions monitoring services to detect and quantify methane and carbon from space. The company’s satellites are the first in the world capable of measuring air emissions from targeted industrial facilities. In November 2020, The New York Times published an article highlighting GHGSat’s satellite technology on using a two-satellite method to pinpoint unknown leaks. The less sensitive satellites are used to identify general areas of leak and then new satellites are used to investigate more closely. The piece also showcased GHGSat’s successful detection last year of a large gas cloud in Turkmenistan that rivaled the biggest known methane leak. Since then, GHGSat has been collaborating with the Netherlands space institute to find large emissions from coal mines in China and Australia, as well as from other oil-and-gas facilities in Central Asia. In October 2020, GHGSat launched its first product called PULSE, a free global map of methane concentration data updated weekly.

Learn More: The Great Climate Opportunity  

Satellites orbit hundreds or even thousands of kilometres above us and we often do not realize the critical role these systems play in our modern society. Every day, satellite technologies are meeting the needs of users around the world, not only helping to keep our lives in order but bringing prosperity. As new technology advances, the importance of, and future uses of, satellites in our everyday lives will only increase. New markets will emerge along with new opportunities to push the boundaries of what space and satellite technology currently offers to us in our daily lives.

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Home — Essay Samples — Information Science and Technology — Digital Era — Satellites And Their Potentials 

Satellites and Their Potentials 

• Categories: Digital Era Information Technology Innovation

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Published: Jan 21, 2020

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Essays on Satellite

• EO Explorer

• Global Maps

A photo-essay from NASA’s Earth Science Division — February 2019 Download Earth in PDF , MOBI (Kindle), or ePub formats.

Of all celestial bodies within reach or view, as far as we can see, out to the edge, the most wonderful and marvelous and mysterious is turning out to be our own planet earth. There is nothing to match it anywhere, not yet anyway. —Lewis Thomas

Sixty years ago, with the launch of Explorer 1, NASA made its first observations of Earth from space. Fifty years ago, astronauts left Earth orbit for the first time and looked back at our “blue marble.” All of these years later, as we send spacecraft and point our telescopes past the outer edges of the solar system, as we study our planetary neighbors and our Sun in exquisite detail, there remains much to see and explore at home.

We are still just getting to know Earth through the tools of science. For centuries, painters, poets, philosophers, and photographers have sought to teach us something about our home through their art.

This book stands at an intersection of science and art. From its origins, NASA has studied our planet in novel ways, using ingenious tools to study physical processes at work—from beneath the crust to the edge of the atmosphere. We look at it in macrocosm and microcosm, from the flow of one mountain stream to the flow of jet streams. Most of all, we look at Earth as a system, examining the cycles and processes—the water cycle, the carbon cycle, ocean circulation, the movement of heat—that interact and influence each other in a complex, dynamic dance across seasons and decades.

We measure particles, gases, energy, and fluids moving in, on, and around Earth. And like artists, we study the light—how it bounces, reflects, refracts, and gets absorbed and changed. Understanding the light and the pictures it composes is no small feat, given the rivers of air and gas moving between our satellite eyes and the planet below.

For all of the dynamism and detail we can observe from orbit, sometimes it is worth stepping back and simply admiring Earth. It is a beautiful, awe-inspiring place, and it is the only world most of us will ever know.

NASA has a unique vantage point for observing the beauty and wonder of Earth and for making sense of it. Looking back from space, astronaut Edgar Mitchell once called Earth “a sparkling blue and white jewel,” and it does dazzle the eye. The planet’s palette of colors and textures and shapes—far more than just blues and whites—are spread across the pages of this book.

We chose these images because they inspire. They tell a story of a 4.5-billion-year-old planet where there is always something new to see. They tell a story of land, wind, water, ice, and air as they can only be viewed from above. They show us that no matter what the human mind can imagine, no matter what the artist can conceive, there are few things more fantastic and inspiring than the world as it already is. The truth of our planet is just as compelling as any fiction.

We hope you enjoy this satellite view of Earth. It is your planet. It is NASA’s mission.

Michael Carlowicz Earth Observatory Managing Editor

The astonishing thing about the Earth... is that it is alive.... Aloft, floating free beneath the moist, gleaming membrane of bright blue sky, is the rising Earth, the only exuberant thing in this part of the cosmos.... It has the organized, self-contained look of a live creature, full of information, marvelously skilled in handling the Sun. —Lewis Thomas, The Lives of a Cell

We shall not cease from exploration, and the end of all our exploring will be to arrive where we started and know the place for the first time. —T.S. Eliot, “Little Gidding”

We shall not cease from exploration, and the end of all our exploring will be to arrive where we started and know the place for the first time. —T.S. Eliot “Little Gidding”

Earth and sky, woods and fields, lakes and rivers, the mountain and the sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books. —John Lubbock, The Use of Life

Earth and sky, woods and fields, lakes and rivers, the mountain and the sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books. —John Lubbock The Use of Life

ice and snow

It seems to me that the natural world is the greatest source of excitement; the greatest source of visual beauty; the greatest source of intellectual interest. It is the greatest source of so much in life that makes life worth living. —David Attenborough

Imagery and data courtesy of:

• NASA Earth Observatory
• U.S. Geological Survey (USGS) and NASA Landsat Program
• International Space Station (ISS) Crew Earth Observations Facility
• LANCE/EOSDIS MODIS Rapid Response Team
• MABEL Science Team
• Level-1 and Atmosphere Archive & Distribution System Distributed Active Archive Center (LAADS DAAC)
• EO-1 Science Team
• Suomi National Polar-orbiting Partnership (Suomi NPP)
• NASA Ocean Biology Processing Group
• NASA/METI/ERSDAC/JAROS/Japan ASTER Science Team

Adapted for the web by Paul Przyborski

About the Authors

Michael Carlowicz is managing editor of the NASA Earth Observatory. He has written about Earth science and geophysics since 1991 for several NASA divisions, the American Geophysical Union, the Woods Hole Oceanographic Institution, and in three popular science books. He is a baseball player and fan, a longtime singer and guitarist, and the proud father of three science and engineering majors.

Kathy Carroll supports the Earth Science Division in the Science Mission Directorate at NASA Headquarters. She previously worked as a manager and organizer at for-profit and non-profit organizations and on political campaigns. She is a diehard baseball and hockey fan, and she volunteers with animal rescue organizations.

Lawrence Friedl directs the Applied Sciences Program in the Earth Science Division of NASA’s Science Mission Directorate. He works to enable innovative and practical uses of data from Earth-observing satellites. He has worked at the U.S. Environmental Protection Agency and as a Space Shuttle flight controller in NASA’s Mission Control Center. He and his wife have three children, and he enjoys ultimate frisbee and hiking.

Stephen Schaeberle is a graphic designer with the Communications Support Services Center at NASA Headquarters. He holds a bachelor of fine arts from the Pratt Institute, and he has received numerous awards and honors for his work and designs. He enjoys boating and fishing on the Chesapeake Bay.

Kevin Ward manages NASA’s Earth Observatory Group, including the Earth Observatory, Visible Earth, NASA Earth Observations (NEO), and EONET. He holds a master’s degree in library and information science and has spent more than 20 years developing Web-accessible resources in support of NASA Earth science communications. He and his wife have a son and a deep love of music.

Acknowledgments

Just a few names end up on the title page of a book, but it takes an entire cast of people to bring it from idea to draft to finished product. The cast for Earth begins with Maxine Aldred, Andrew Cooke, Tun Hla, and Lisa Jirousek, who shepherded the words and images through design and layout. Thanks are also due to Kathryn Hansen, Pola Lem, Rebecca Lindsey, Holli Riebeek, Michon Scott, and Adam Voiland, whose reporting and writing contributions gave this book its depth. Joshua Stevens, Robert Simmon, Jesse Allen, Jeff Schmaltz, Michael Taylor, and Norman Kuring applied their strong visual sense and processing skills to make each image pop with color and texture while remaining scientifically accurate.

We owe a debt to our scientific and outreach colleagues, who keep the satellites running, the sensors sensing, and the data and imagery flowing. Every one of the images in this book is publicly available through the Internet, truly making science accessible to every citizen. The Landsat teams at the U.S. Geological Survey and NASA, the LANCE/EOSDIS MODIS Rapid Response Team, and the NASA Earth Observatory deserve extra gratitude for making our planet visible to the scientist and the layman every day.

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Satellite - Free Essay Examples and Topic Ideas

A satellite is a man-made device that orbits the Earth or other celestial objects. It is designed to perform various tasks such as communication, navigation, imaging, weather monitoring, and scientific research. Satellites can be classified into different types based on their orbits, functions, size, and configuration. They are powered by solar panels and can transmit data using radio signals to ground stations or other satellites. Satellites have revolutionized the way we live and work, enabling us to communicate and access information from anywhere on the planet.

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Earth Observations from Space: The First 50 Years of Scientific Achievements (2008)

Chapter: 12 conclusions.

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12 Conclusions Just as the invention of the mirror allowed humans to see their coverage than obtained during the intensive field expeditions own image with clarity for the first time, Earth observations of the IGY from the comfort of their desktops. from space have allowed humans to see themselves for the The advent of satellites revolutionized the Earth sci- first time living on and altering a dynamic planet. ences. They provided the first complete global record of biological, physical, and chemical parameters such as cloud THE EMERGENCE OF INTEGRATED cover, winds, and ice cover. They provided consistency of EARTH SYSTEM SCIENCE coverage not available with ground measurements. Time series data revealed large-scale processes and features that During the International Geophysical Year (IGY) of could not have been discovered by other ways. Prior to the 1957-1958, 67 nations cooperated in an unprecedented effort availability of satellite-based observations, scientists seek- to study the Earth. In an age otherwise characterized by ing global perspectives from largely ground-based observa- Cold War tensions, the noted geophysicist Sydney Chapman tions were required to develop international collaborations (1888-1972) referred to the IGY as “the common study of and launch large-scale field campaigns. Piecing together our planet by all nations for the benefit of all.” This global data points required interpolation and extrapolation to fill effort laid the foundation for the integration of Earth sci- data gaps, particularly for remote locations. In addition, ences and demanded widespread simultaneous observations. large-scale sampling efforts involved extensive logistics It involved large teams of observers, many of whom were and advance planning, which prohibited frequent repetition. deployed to the ends of Earth—in polar regions, on high Because the rate of change of many parameters of interest mountaintops, and at sea—to study meteorology, oceanog- is much greater than the rate at which global maps could be raphy, glaciology, ionospheric physics, aurora and airglow, produced in the presatellite era, it was impossible to observe seismology, gravity, geomagnetism, solar radiation, and the full dynamics of the system. cosmic rays. Even in 1957 it was recognized that satellite Therefore, the unique and revolutionary vantage point data would bring observations of Earth that no amount of from space provides scientists with global images and maps ground-based observations could achieve. of parameters of interest unmatched by any ground-based Hundreds of sounding rockets were launched into the observing technology in terms of frequency and coverage. upper atmosphere and near space during the IGY, and the Because satellites collect data continuously and allow for “space age” officially began with geophysical satellites, daily (or at least monthly averaged) global images, changes although still in their infancy, playing an important role can be observed at the relevant temporal and spatial scale (Chapter 2). During the IGY the Soviet Union launched the required to detect Earth system processes. The full ­dynamics world’s first satellite, Sputnik, in October 1957. The United of the system have only been observed or characterized States launched its first satellite, Explorer 1, shortly there­after since the advent of satellite observations and have allowed in January 1958. Over the course of the next five decades, the the study of previously inaccessible phenomena such as United States and its international partners have launched an stratospheric ozone creation and depletion, the transport of array of satellites that fundamentally altered our understand- air pollution across entire ocean basins from China to the ing of the planet. A half-century later, Earth scientists can continental United States (Chapter 5), global energy fluxes acquire global satellite data with orders of magnitude greater (Chapter 4), ice sheet flow (Chapter 7), global primary pro- 98 

CONCLUSIONS 99 ductivity (Chapter 9), ocean currents and mesoscale features summer ice over the past decades (Chapter 7). Satellite (Chapter 8), and global maps of winds (Chapter 8). Prior to observations have become available and matured as scientific the satellite era, even if it was possible to compose a global data at a time when they are critically important in helping picture from individual surface observations (e.g., through society manage planetary-scale resources and environmental the World Weather Watch, established in 1963), the coverage challenges. Although many scientific challenges remain, it is and density of the network and lack of vertical resolution undeniable that satellite observations have allowed scientists left much to be desired. Other geophysical and biological to improve the ability to monitor and predict changes in the phenomena were sampled much less frequently, often as a Earth system and manage life on Earth (NRC 2007a). partial “snapshot” of an otherwise dynamic set of interacting It is widely known that satellite data, particularly from Earth processes. the southern hemisphere, have contributed to improvements Discovery of the variability in the velocity of ice sheet in weather prediction, resulting in protection of human lives flow is another example of how the dynamics of the sys- and infrastructure (Chapter 3). Since the availability of sat- tem went undetected until reliable and repeated satellite ellite images, no tropical cyclone has gone undetected, and observations became available (Chapter 7). This discovery the advance warning allows crucial time to prepare. In fact, revolutionized the study of ice sheet flow and yielded an the advent of satellites has been heralded as unquestionably important realization: sea-level change due to freshwater “the greatest single advancement in observing tools for input from the continental ice sheets was not a function of tropical meteorology” (Sheets 1990). Furthermore, because the balance between ice sheet melting and precipitation at satellite data give access to the largely undersampled ocean, higher elevation, but a function of the flow dynamics. The hurricane track forecasts have improved dramatically, help- increasing velocity of continental ice flow into the ocean in ing save lives and property every year (Considine et al. response to climate change and the collapse of the Larsen B 2004). Other aspects of human welfare have and will also Ice Shelf emphasized the sensitivity of ice sheet dynamics benefit from satellite observations. For example, it is also to a changing climate. unlikely that a famine early warning system would be avail- Satellite sensors provide a panoptic viewpoint, yet his- able to assist in planning aid distribution without the ability torically they suffered from poor resolution and calibration to observe vegetation cover and the availability of water problems. On the other hand, ground-based instruments, resources from space (Chapter 10). Given the projected although more precise and better calibrated, are limited to climate change and associated sea-level rise, having global their particular locales, and problems arise since they must be satellite coverage available in the future will serve crucial coordinated and intercalibrated with other ground stations. societal needs unmet by any other observing system. As satellite sensors and data processing have become more sophisticated, equaling or surpassing those for ground-based Conclusion 1: The daily synoptic global view of measurements, scientists have obtained not only images but Earth, uniquely available from satellite observations, has also quantitative global measurements of unprecedented revolutionized Earth studies and ushered in a new era of precision. Intercalibration proved particularly challenging in multidisciplinary Earth sciences, with an emphasis on putting together global maps of marine primary productiv- dynamics at all accessible spatial and temporal scales, ity from shipboard measurements (Chapter 9). Estimating even in remote areas. This new capability plays a criti- marine primary productivity requires sample manipulation cally important role in helping society manage planetary- and measurements of 14C uptake rates at each location, scale resources and environmental challenges. which are sensitive to variations in sampling techniques and methods. Although global marine primary productivity INTEGRATED GLOBAL VIEW OF THE CARBON CYCLE estimates had been attempted before the satellites era, they AND CLIMATE SYSTEM were flawed because of intercalibration issues. More impor- tantly, because it takes years to obtain global coverage of The global view of Earth from satellites has imparted ground-based marine primary productivity measurements, the understanding that everything is connected—land, ocean, satellites allowed for the first time observation of global and atmosphere. Interdisciplinary teams of ­researchers have marine primary productivity on a monthly and annual basis explored these connections to better understand the Earth and detection of decadal-scale trends. as a system beyond the sum of its elements. The concept Satellite observations also provide access to otherwise of studying the Earth as an integrated system at a national virtually inaccessible regions, such as polar regions, the upper level was led by the National Aeronautics and Space atmosphere, and the open oceans. Quantitative assessment Administration (NASA), inspired by NASA’s “Ride report” and monitoring of the sea ice extent in the Arctic has only (NASA 1987), and intended as the U.S. component to the been possible since routine satellite observations became International ­Geosphere-Biosphere Program. Consequently, available. Without satellite images, it is unlikely that trends in NASA launched its mission to planet Earth to study the decreasing Arctic summer sea ice would have been detected Earth’s geosphere and biosphere as an integrated system as readily, demonstrating univocally the drastic decline in instead of discrete but interrelated components (CRS 1990). 

100 EARTH OBSERVATIONS FROM SPACE: THE FIRST 50 YEARS OF SCIENTIFIC ACHIEVEMENTS Other nations have also made significant contributions to which in turn affects the amount of carbon dioxide (CO2) the ­capacity to observe Earth from space. This multinational uptake (Chapter 9); and water vapor is important as a investment has enabled much international collaboration greenhouse gas and in heat exchange processes between the among satellite projects. ocean, land, and atmosphere (Chapters 3, 4, 8, and 9). Due A prime example of an interdisciplinary research to water’s relatively high specific heat capacity and its large- endeavor is the study of the global carbon cycle, which scale circulation, the ocean plays a central role in storing and employs a wide range of research approaches such as ground transporting Earth’s heat content (Chapter 8). In fact, more and satellite observations, modeling studies, and laboratory than 80 percent of Earth’s heat is stored in the ocean. Improv- experiments. The well-known Keeling curve was obtained ing our understanding of ocean circulations and consequently from in situ observations and revealed atmosphere-biosphere the transport of heat is a major challenge to more accurate interactions, as well as the long-term trend of increasing climate models and predictions. Lastly, the above-mentioned atmospheric carbon dioxide (Keeling et al. 1976). These find- advances in understanding the global carbon cycle further the ings launched major efforts in understanding the role of the ability to predict future atmospheric CO2 levels. terrestrial and oceanic biosphere in carbon uptake through The long-term observations obtained during the past 50 photosynthesis and the impact of increased carbon dioxide years of Earth science from space combined with advances levels on global climate. However, primary productivity is in data assimilation, computer models, and ground-based controlled by geophysical processes; thus, understanding the process studies brought climate scientists to the point at interconnections, such as the effect of a changing climate which they could begin to project how climate change will and hydrologic cycle on the global biosphere and vice versa, affect weather and natural resources at the regional level, required observations at a global scale of land-cover changes the scale at which the information is of greatest societal (from Landsat and AVHRR [Advanced Very High Resolu- relevance (NRC 2001a). tion Radiometer]; see Chapter 11), biomass estimates and This comes at a time when improved understanding of primary productivity (AVHRR, CZCS [Coastal Zone Color the climate system is central to the viability of our economy, Scanner], SeaWiFS [Sea-viewing Wide Field-of-view Sen- as seasonal-to-interannual climate fluctuations strongly sor], and MODIS [Moderate Resolution Imaging Spectrora- influence agriculture, the energy sector, and water resources diometer]; see Chapters 9 and 10), changes in the hydrologic (CCSP 2003). However, important scientific challenges—for cycle (Landsat, AVHRR, MODIS, and Topography Experi- example, cloud-water feedback in climate models—must be ment (TOPEX)/Poseidon; see Chapters 6 and 7) and climate conquered with the aid of continuous satellite data before (AVHRR, MODIS, and SeaWiFS). Once the data were avail- the appropriate seasonal-to-interannual climate information able, major scientific advances came from assimilating them can be made readily available at the appropriate scale (NRC into three-­dimensional coupled modeling of the atmosphere, 2007a). The Earth science community has built over the past land, ocean, and cryosphere (Fung 1986, Heiman and Keel- decades the capacity to incorporate all the pieces into an ing 1986, Fung et al. 1987, Keeling et al. 1989). integrated systems perspective, thanks to ever more sophis- Equally interdisciplinary in nature is climate change ticated models. As the community is now poised to make research. In fact, many of the accomplishments highlighted major advances in climate science and predicting climate in this report have contributed to the improved understand- changes at various scales, the ability to provide sustained ing of the climate system and laid the groundwork modeling multidecadal global measurements is crucial (NRC 1999, for projecting climate change. One notable example is the 2001b, 2007a). long-term observations of Earth’s radiation budget, which The ability to observe and predict El Niño/La Niña revealed the role of the ocean and atmosphere in transporting conditions in advance of their full manifestation based on heat and the role of aerosols from the volcanic eruption of satellite and in situ data illustrates the significant break- Mount Pinatubo in cooling the climate (Chapter 4). With the through climate scientists have made in providing impor- understanding of the importance of aerosols to the climate tant regional climate information to resource managers system comes the need to observe continuously both natural (Box 12.1, Figure 12.1). and anthropogenic sources of aerosols (Chapter 4). Satellite As many accomplishments have shown, the length and observations have also been central in revealing the role of continuity of a given data record often yield additional sci- important gases, such as water vapor and ozone, in the cli- entific benefits beyond the initial research results of the mis- mate system (Chapters 4 and 5). sion and beyond the monitoring implications for operational Long-term observations of water in each phase are agencies. For example, the effect of aerosols from a volcanic central to understanding the climate system: sea ice contrib- eruption (Mount Pinatubo) on the global climate would utes to Earth’s albedo and its decrease not only indicates a have gone undetected without the continuous observations warmer climate but is also a positive feedback (Chapter 7); of the Earth Radiation Budget Experiment (ERBE, Chapter melting of continental ice sheets contributes to sea-level 4). Thus, maintaining well-calibrated long-term data sets is rise (Chapter 7); the availability of liquid water is important likely to yield important scientific advances in understanding in controlling the productivity of the terrestrial ecosystem, the Earth system, in addition to contributing to societal appli- 

CONCLUSIONS 101 cations. The importance of stable, accurate, intercalibrated, to measure the geopotential and mean sea level to determine long-term climate data records is universally recognized, and the general circulation of the oceans and resolve the spatial strategies on how to collect and maintain such data streams variations of the gravity field as a goal for geophysics and have been provided in many previous reports (NRC 1985, physical oceanography. NASA responded to this challenge 2000, 2001b, 2003, 2004). Important elements to successful by launching three satellites within 9 years following the long-term climate data from satellites include a long-term Williamstown conference, with Seasat—the third and most strategy to guarantee that follow-on missions overlap to advanced satellite—providing accurate ocean elevation allow for cross-calibrations, leadership in data stewardship with a precision to tens of centimeters. For the first time the and management, and strong interagency collaborations. bathymetry of the ocean floor could be observed from space, Follow-on missions maximize the return on previously revealing the large mid-Atlantic ridges and trenches (Chap- made investments in technology development, including sen- ter 11). As the precision of altimetry data further increased sors and data analysis tools. Missions designed for process the importance of eddies in the mixing of the open ocean was studies of initially short durations may provide significant discovered (Chapter 8). scientific value by continuing a given data record in the It is common for any given satellite or instrument in context of global change research. The value of a continuous space to supply data that may be used in multiple fields of data record increases significantly through the development Earth science by design or serendipitously (see Table A.1). of uninterrupted follow-on missions, particularly if careful Although Landsat was designed to observe changes on land, cross-calibrations between subsequent generations of satel- including the terrestrial ecosystem, assembling the approxi- lite sensors are undertaken (NRC 2004). The long-term data mately 5,000 individual images for a global time series records from Landsat and AVHRR exemplify the scientific proved to be too computationally intensive. Instead, it was value of such carefully maintained data streams (Chapters 9 AVHRR data—designed to monitor the atmosphere—that and 10). turned out to be invaluable to producing global terrestrial primary productivity estimates. Due to careful intercalibra- Conclusion 2: To assess global change quantitatively, tions between the different sensors, the AVHRR data record synoptic data sets with long time series are required. The now extends over 20 years (Chapter 8) and has allowed value of the data increases significantly with seamless and the detection of trends in terrestrial primary productivity intercalibrated time series (NRC 2004), which highlight (Chapter 9). In fact, data from AVHRR have also been used the benefits of follow-on missions. Further, as these time in many other fields to study processes such as snow cover, series lengthen, historical data sets often increase in sci- sea surface temperature, cloud optical properties, and global entific and societal value. land-cover change (Chapters 6, 8, and 10). The design of MODIS illustrates the potential for using a single instrument to serve many applications. Its spectral MAXIMIZING THE RETURN ON INVESTMENT IN bands were designed to serve a diversity of user commu- EARTH OBSERVATIONS FROM SPACE nities in the Earth sciences, allowing observations of the As scientists have gained experience in studying Earth following parameters: land, cloud, and aerosol properties; through satellite observations, they have defined new tech- ocean color and marine biogeochemistry; atmospheric water nology needs, helped drive technology development to vapor; surface and cloud temperature; cloud properties; provide more quantitative and accurate measurements, and cirrus cloud water vapor; atmospheric temperature; ozone; advanced more sophisticated methods to interpret satellite and cloud top altitude. It has led to scientific breakthroughs data (Chapter 2). Many scientific accomplishments have such as discovery of the brown clouds (Chapter 4), measur- resulted from rapid satellite technology development that ing marine primary productivity annually (Chapter 9), and responded to scientific needs and provided capabilities that observation of optical depth and effective particle radius in enabled major advances in the Earth sciences. The value of low clouds (Chapter 4). Because of the potential to design satellite observations from space grows dramatically as new, missions with spectral bands that can serve many different more accurate instruments are developed. Initially, satel- scientific user communities, creating follow-on missions lites provided a means for acquiring pictures. Now, satellite that continue measurements—and thus ensure the long- image acquisition and interpretation provide quantitative term climatic data records discussed above—does not have geo­physical or biological variables by transforming measure- to come at an increased cost or at the cost of research and ments of reflected or emitted electromagnetic radiation into development missions. desired parameters. For many applications such as ocean In addition, the measurement of a given variable, in and land topography, ice sheet dynamics, and concentra- some cases from multiple sensors, often contributes to tions of atmospheric gases, observations are scientifically several fields of Earth science. For example, few scientific valuable if they can be made with great accuracy, which has accomplishments are as “transformative” as the advances in driven technology evolution. For example, the Williamstown space geodesy over the past five decades (Chapter 11). This report (NASA 1970) outlines the need for satellite sensors breakthrough has not only transformed the field of geodesy 

102 EARTH OBSERVATIONS FROM SPACE: THE FIRST 50 YEARS OF SCIENTIFIC ACHIEVEMENTS BOX 12.1 El Niño-Southern Oscillation El Niño is a condition that has been known for well over a century. In some years waters off the west coast of South America would become warmer than usual, and the fish populations normally found there would disappear, bringing hardship to fishermen in the region. It occurs periodically around Christmastime and thus was named “El Niño”—the Spanish term referring to the Christ Child. Much of the groundwork for understanding and describing the El Niño-Southern Oscillation (ENSO) as a coupled atmosphere-ocean phenomenon was laid in the 1970s and 1980s and based on in situ data and modeling studies (e.g., Rowntree 1972, Wyrtki 1975, Rasmusson and Carpenter 1982, Zebiak 1982, Shukla and Wallace 1983, Cane 1984). However, satellite data confirmed observations and model efforts and revealed the global impact of ENSO (Friedler 1984). The improved understanding of the atmosphere-ocean connection has improved the ability to predict ENSO conditions and has advanced our understanding of the teleconnections and impacts on the marine and ter- restrial biosphere (Barber and Chavez 1983). In normal years winds blow from east to west, causing warm surface waters to “pile up” in the western tropical Pacific. During an El Niño, the winds relax and the warm surface waters flow back toward the eastern Pacific. Wind- driven upwellings do not reach deep enough to bring nutrients from below the thermocline. Without the supply of nutrients, phytoplankton do not thrive and this creates a chain reaction in the marine ecosystem. The major El Niño event of 1982 revealed its impacts not only on the ocean but also on global weather patterns, which invigorated re- search efforts to improve ENSO predictions. Because ENSO events are accompanied typically by drought conditions in Indonesia and Australia and heavier-than-normal rainfall in South America, their effects can be seen in virtually every form of Earth observations from space. By piecing together the different observations (sea surface temperature [SST], winds, sea surface height, biological productivity, rainfall, and land cover), scientists are working to develop theories to explain what triggers an El Niño and to predict consequences once an El Niño has developed. Satellite observations of SST and winds combined with in situ data are also used to predict El Niño events up to a year in advance. Figure 12.1 illustrates­ how the physical and biological properties of the Pacific are related during an El Niño and the opposite, La Niña, condition. FIGURE 12.1  These images of the Pacific Ocean show conditions during an El Niño (1997) and La Niña (1998). The upper images were produced using sea surface height measurements made by the U.S.-French TOPEX/Poseidon satellite. They show variations in sea surface height relative to normal conditions as an indicator of the amount of heat stored in the ocean. The two lower images show variability in chlorophyll concentration relative to normal levels as a measure of phytoplankton biomass. These were produced using data from SeaWiFS. In 1997 the warm surface water in the eastern Pacific (shown in white in the upper figure) was 14 to 32 cm (6 to 13 in.) higher than normal and about 10 cm (4 in.) above normal in the red areas. The same waters were abnormally low in chlorophyll (shown in blue in the lower image) because the supply of nutrients from upwelling was greatly reduced. This El Niño condition results in the well-known absence of fish off the west coast of South America. The images for 1998 show the low sea level or a cold pool of water (shown in purple in the upper image) during the La Niña phase. The lower figure shows higher- than-average chlorophyll (yellow) associated with this cold pool. During La Niña, nutrients were upwelled into the cold pool, resulting in an extensive phytoplankton bloom at the equator that lasted for several months. SOURCE: NASA Jet Propulsion Laboratory (top row); provided by J. Campbell and based on data from SeaWiFS Project, NASA Goddard Space Flight Center, and GeoEye (bottom row). 

CONCLUSIONS 103 a b Mapped – 1997 Mapped – 1998 c d 12-1 a,b,c,d 

104 EARTH OBSERVATIONS FROM SPACE: THE FIRST 50 YEARS OF SCIENTIFIC ACHIEVEMENTS but also provided vital information for studying global sea- increasingly important in pushing satellite sensors to provide level change, earthquakes, and volcanoes. Furthermore, more quantitative and accurate measurements. Ocean buoys Earth scientists from all disciplines rely on an International and drifters as well as shipboard observations have been Earth Reference Frame from which geographical positions used extensively to validate sea surface temperature, ocean can be accurately described relative to the geocenter, in three- color, and wind observations from satellites (Chapter 8). In dimensional Cartesian coordinates to centimeter accuracy or addition, as satellite data have become more quantitative and better—a 2 to 3 orders of magnitude improvement compared more readily used by the broader research community, they to 50 years ago. have contributed to field campaigns and altered the scientific Measured by AVHRR and SAGE (Stratospheric ­Aerosol endeavor. For example, ground-based campaigns are more and Gas Experiment), aerosols represent a geophysical effectively planned and guided because of the information variable important to Earth’s radiation budget, air ­ quality made available from satellite observations. forecasts, cloud formation affecting weather forecasts, Just as the synergy between satellite and ground-based and hydrologic applications (Chapter 4). Thus, a scientific observations yields new insights, so does the combination accomplishment in one field can lead to major advances in of satellite observations from different instruments. Thus, other fields and drive interdisciplinary research efforts. The to capitalize fully on some investments in satellite sensors, advances in understanding and predicting El Niño-Southern simultaneous measurements are necessary. The recent analy- Oscillation (ENSO) conditions exemplify the advantage of sis of the merged altimetry data set from TOPEX/Poseidon studying the Earth as an integrated system and the benefit of and the European Remote Sensing Satellite (ERS) revealed combining in situ and satellite observations with modeling the prevalence of westward-propagating eddies not seen from studies. individual sensors (Chapter 8). This discovery would not have been possible without merging the two data sets from Conclusion 3: The scientific advances resulting from the individual sensors. Earth observations from space illustrate the successful synergy between science and technology. The scientific Conclusion 4: Satellite observations often reveal and commercial value of satellite observations from known phenomena and processes to be more complex space and their potential to benefit society often increase than previously understood. This brings to the fore the d ­ ramatically as instruments become more accurate. indisputable benefits of multiple synergistic observations, including orbital, suborbital, and in situ measurements, The observational vantage point from space added a new linked with the best models available. appreciation for the complexity of many previously known Earth science processes. Because of the problem of spatial The greatest benefit of Earth observations from space and temporal undersampling by ground-based observing is gained when data are integrated into state-of-the-art tools, composing a synoptic view required interpolation m ­ odels, combined with ground-based observation net- across data gaps. Consequently, more complex features work and process studies, and analyzed with sophisticated were averaged out through the interpolation process and methods. Model development has aided in developing an not revealed until satellites observed these features directly. inter­disciplinary thinking in the Earth sciences. Building Similarly, the frequency of synoptic views available from sophisticated models and data analysis tools often involves daily satellite overflights made an unprecedented temporal long lead times and requires training of a skilled workforce. resolution available. As altimetry measurements became Consequently, the major scientific breakthrough might accurate to the centimeter scale, they revealed how highly f ­ ollow years after the satellite data have first become avail- time dependent and essentially turbulent the ocean was, able. To capitalize fully on the investment, satellite data also which is in contrast to the presatellite view that the ocean was require careful calibration (NRC 2004). In addition, building primarily in steady state with slowly changing, large-scale long-term data records for climate research requires cross- circulation (Chapter 8). This resulted in a ­paradigm shift with and intercalibration between various sensors and follow-on implications for climate change research that have yet to be missions, data processing and archiving, and maintenance of fully understood (Wunsch 2007). the metadata (NRC 2004). In the case of many scientific accomplishments, signifi- To develop the aforementioned infrastructure and data cant results are not solely based on satellite data but include assimilation and analysis tools, scientists need to be trained in situ data and model components. In fact, the value of in using and analyzing satellite data. Thus, investment in space-based observations increases with well-coordinated training and supporting a remote sensing community is ground-based observations, suborbital observations, and/or important to guaranteeing scientific advances from satellite cross-calibration among satellites with complementary instru- data (NRC 2007a). Attracting young scientists to the field of ments. Ground-based observations also provide an important remote sensing is made easier by the prospect of stability in “surface validation” for satellite data and are used to calibrate the satellite data supply. In contrast, data gaps may result in spaceborne instruments. Such surface validations become the loss of a highly specialized workforce (NRC 2007a). The 

CONCLUSIONS 105 full benefit of satellite data is only realized when a robust OPPORTUNITIES FOR THE FUTURE OF scientific community is trained to use the data to address EARTH OBSERVATIONS FROM SPACE fundamental and applied research questions. Fifty years from now a report similar to this one is The Landsat story, described in numerous accounts (e.g., likely to describe many more astounding discoveries about NRC 2002), is a case in point: wholesale commercialization the Earth system, if the commitment to satellite observations of the data led to a precipitous drop in their use for science from space is sustained. Although this report provides an and commercial applications, which recovered upon return extensive sampling of important accomplishments enabled to the earlier policy that made data access affordable. Only by Earth satellite data, many scientific questions and societal when academic, government, and commercial scientists challenges remain unresolved, including improving 10-day are given liberal access to data and a sufficient number are weather forecasts, more accurately forecasting hurricane trained in the effective use of these data will the analysis intensity, increasing resolution of earthquake fault systems tools mature to the benefit of all parties. Similarly, obtain- and volcanoes to detect precursors of events, mitigating ing the maximum benefit from weather satellites required a climate change impacts, and protecting natural resources decade-long process of improving methods of radiance data (NRC 2007a). assimilation (Lord 2006; see Chapter 3). Because the critical infrastructure to make the best use of satellite data takes decades to build and is now in place, the Conclusion 5: The full benefits of satellite observa- scientific community is poised to make significant ­progress tions of Earth are realized only when the essential infra- toward understanding and predicting the complexity of the structure, such as models, computing facilities, ground Earth system. However, building a predictive capability relies networks, and trained personnel, is in place. strongly on the availability of seamlessly intercalibrated long-term data records, which can only be maintained if NASA’s open and free data policy has created a world- subsequent generations of satellite sensors overlap with wide linked community of Earth scientists. This open-access their predecessors. Unfortunately, the current capability to policy encourages use of the data for scientific purposes and observe Earth from space is jeopardized by delays in and lack maximizes the potential societal benefits of the observations. of funding for many critical satellite missions (NRC 2007a). The long list of accomplishments is unlikely to have mate- Because important climate data records and important Earth- rialized without this open data policy that encouraged the observing missions are at risk of suffering detrimental data growth of the field (NRC 2004). As previously mentioned, gaps or of being cut altogether, the committee strongly agrees when the Landsat program was privatized during the late with the following recommendation by the decadal survey 1980s and early 1990s, the data became so costly that it (NRC 2007a): severely hampered the research program (Malakoff 2000), illustrating the importance of maintaining free or affordable The U.S. government, working in concert with the data streams. private sector, academe, the public, and its international Open access also increases the societal benefits of the partners, should renew its investment in Earth-observing data by allowing nations without the observational capa- systems and restore its leadership in Earth science and bilities of the developed world to gain access to important applications. environmental observations. The Famine Early Warning System Network, although developed by a U.S. agency, is an To sustain the rate of scientific discovery and advances, example of such an application that aids developing nations committing to the maintenance of long-term observing in resource management without having to first build the capacities and to innovation in observing technology is ground-based observational capabilities. Consequently, data equally important. Because past observations taught scien- sharing among agencies and other countries leads to more tists that the Earth is a highly dynamic system and not as than the sum of its parts, particularly if nations with Earth- predictable as initially assumed, long-term observations are orbiting satellites collaborate on an international strategy required if humans wish to understand and predict future regarding the important satellite missions and data needs to changes. Future advances will be associated with tremendous observe the Earth system (NRC 2007a). societal benefits, given the current challenges presented, for example, by climate change and loss of biodiversity. One can Conclusion 6: Providing full and open access to global envision the availability of regional annual climate predic- data to an international audience more fully capitalizes tions to assist in water resource management, an infectious on the investment in satellite technology and creates a disease early warning system, operational use of air pollution more interdisciplinary and integrated Earth science com- maps, and improved ability to foresee volcanic eruptions or munity. International data sharing and collaborations on earthquakes (NRC 2001a, 2007a). satellite missions lessen the burden on individual nations The committee strongly agrees with the following lines to maintain Earth observational capacities. from the interim report of the decadal survey (NRC 2005): 

106 EARTH OBSERVATIONS FROM SPACE: THE FIRST 50 YEARS OF SCIENTIFIC ACHIEVEMENTS Understanding the complex, changing planet on Conclusion 7: Over the past 50 years, space observa- which we live, how it supports life, and how human tions of the Earth have accelerated the cross-disciplinary activities affect its ability to do so in the future is one of integration of analysis, interpretation, and, ultimately, the greatest intellectual challenges facing humanity. It is our understanding of the dynamic processes that govern also one of the most important challenges for society as it the planet. Given this momentum, the next decades will seeks to achieve prosperity, health, and sustainability. bring more remarkable discoveries and the capability to predict Earth processes, critical to protect human lives If the nation’s commitment to continue Earth observa- and property. However, the nation’s commitment to tions from space is renewed, we have seen just the beginning Earth satellite missions must be renewed to realize the of an era of Earth observations from space, and a report in 50 potential of this fertile area of science. years will be able to highlight many more valuable scientific achievements and discoveries. 

Over the past 50 years, thousands of satellites have been sent into space on missions to collect data about the Earth. Today, the ability to forecast weather, climate, and natural hazards depends critically on these satellite-based observations. At the request of the National Aeronautics and Space Administration, the National Research Council convened a committee to examine the scientific accomplishments that have resulted from space-based observations. This book describes how the ability to view the entire globe at once, uniquely available from satellite observations, has revolutionized Earth studies and ushered in a new era of multidisciplinary Earth sciences. In particular, the ability to gather satellite images frequently enough to create "movies" of the changing planet is improving the understanding of Earth's dynamic processes and helping society to manage limited resources and environmental challenges. The book concludes that continued Earth observations from space will be required to address scientific and societal challenges of the future.

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Space Exploration and Satellites

By: Edouard Mathieu and Max Roser

Space exploration and the study of outer space have fascinated humans for centuries. In recent decades, we have significantly advanced our understanding of the universe and our place within it. Space travel and exploration have opened up new frontiers and possibilities for humanity, from the first manned mission to the moon in 1969 to the ongoing efforts to send humans to Mars.

In addition to manned missions, we have also sent satellites into orbit around the Earth. These satellites serve various purposes that have revolutionized our lives, including communication, weather forecasting, surveillance, and environmental monitoring.

But, as our presence in space has increased, so has the issue of pollution. Our many launches into space have created debris, including abandoned rocket stages, old satellites, and other discarded equipment. This debris poses a significant risk to future space exploration, as it can collide with and damage functioning satellites or even endanger astronauts on space missions. This is an ongoing challenge that will require continued research and innovation to solve.

This page provides data and visualizations on space exploration, satellites, space pollution, and astronomical research.

Interactive Charts on Space Exploration and Satellites

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Satellite Imagery: Strengths and Weaknesses Essay

• To find inspiration for your paper and overcome writer’s block
• As a source of information (ensure proper referencing)
• As a template for you assignment

Introduction

Visible satellite imagery, infrared satellite imagery, vapor satellite imagery, fog satellite imagery.

The invention of the satellite was vital to exploring the planet from above by revealing features that had not been seen. The technology has been used to capture images of landscapes and other fascinating features on the earth. Weather forecasters and flight directors rely on this technology to give reliable information to the public and the cabin crew. Many astronauts and space researchers depend on satellite imagery as a weather forecasting system to schedule their space missions. Various types of technology present significant opportunities as well as drawbacks that impact their overall applications.

Visible satellite imagery uses sunlight to record images, making it work well during the day. This technology possesses the ability to display the difference between underlying fog and stratus, which other imaging technologies like Infrared imagery may not capture, provided such areas are not blocked from view by higher clouds (Felegari et al., 2021). Contrary to the advantages mentioned above, the University of Wisconsin Department of Atmospheric and Oceanic Sciences indicates that visible imagery is only useful during the daylight hours, making it difficult to distinguish low clouds from high clouds since all clouds reflect a similar amount of light (Felegari et al., 2021). In addition, it is challenging to distinguish snow from clouds, which may lead to unreliable data.

Infrared imagery uses emitted wavelengths to record images, which can be done during the day or night. The University of Wisconsin, Department of Atmospheric and Oceanic Sciences, states that this technology has the ability to distinguish higher clouds from lower ones. Furthermore, it makes it possible to observe storms at night using this imagery, in addition to differentiating clouds from snow cover (Zou et al., 2021). It is unreliable for detecting low clouds at night because the temperature emitted by underlying clouds and fog is somewhat the same as in surrounding areas

This technology is often applied to detect the presence of vapor above twenty thousand feet in the atmosphere. It is mainly used to forecast and analyze the paths in addition to higher level motion of moisture when multiple such images are looped together (Gadamsetty et al., 2022). This technology is used to give pilot briefings and directions because it detects jet streams and high headwinds. It is vital for identifying mountain wave turbulence on airways even under clear visibility. Despite being used in flight control, Vapor Imagery does not show the presence of low clouds or water vapor content below the effective layer. Similarly, it is unable to give the measure of atmospheric vapor below the effective layer.

Finally, fog satellite imagery, like visible images, is majorly useful during the day only because if a fog lies between the middle and upper clouds, it becomes difficult to detect due to limited grey scale variability. In comparison to visible imagery, this technology displays smoother images. Therefore its accuracy can be hampered by contrasting temperatures between cloud top and the surrounding sea and when the land surface is small.

Satellite technology is vital in day-to-day global operations; weather forecasting, air travel, and space travel all rely on the data acquired by this technology. This invention has expanded human knowledge about the planet and the solar system by revealing secret features on earth and remarkable images of the galaxy. The four types of Satellite imagery we have discussed have advantages and disadvantages; however, the accuracy and the reliability of the data generated by each system depend on the time of day it is appropriate to be used. There is some visible imagery that is more reliable during daylight, whereas others, including infrared and water vapor, can be reliable both at night and during sunlight.

Felegari, S., Sharifi, A., Moravej, K., Amin, M., Golchin, A., Muzirafuti, A., Tariq, A. & Zhao, N. (2021). Integration of Sentinel 1 and Sentinel 2 satellite images for crop mapping . Applied Sciences , 11 (21), 10104. Web.

Gadamsetty, S., Ch, R., Ch, A., Iwendi, C., & Gadekallu, T. R. (2022). Hash-based deep learning approach for remote sensing satellite imagery detection . Water , 14 (5), 707. Web.

Zou, Y., Zhang, L., Liu, C., Wang, B., Hu, Y., & Chen, Q. (2021). Super-resolution reconstruction of infrared images based on a convolutional neural network with skip connections . Optics and Lasers in Engineering , 146 , 106717. Web.

• Powerful Impacts of the Use of Gadgets and the Internet
• Modern Technologies' Impact on Global Community
• The “Vapor Storms” Article by Jennifer A. Francis
• Infrared Radiation and Its Impact on Life
• The Relevance of Clausewitz’s Fog and Friction in a Digital Age
• The Impact of Smartphones on Mental and Emotional Well-Being
• New Technology's Influence on the Future
• Microwave Radiation's Impact on Different Microorganisms
• Modern Technologies: Impact on Employment
• The Impact of Spotify on the Consumption Industry
• Chicago (A-D)
• Chicago (N-B)

IvyPanda. (2024, January 29). Satellite Imagery: Strengths and Weaknesses. https://ivypanda.com/essays/satellite-imagery-strengths-and-weaknesses/

"Satellite Imagery: Strengths and Weaknesses." IvyPanda , 29 Jan. 2024, ivypanda.com/essays/satellite-imagery-strengths-and-weaknesses/.

IvyPanda . (2024) 'Satellite Imagery: Strengths and Weaknesses'. 29 January.

IvyPanda . 2024. "Satellite Imagery: Strengths and Weaknesses." January 29, 2024. https://ivypanda.com/essays/satellite-imagery-strengths-and-weaknesses/.

1. IvyPanda . "Satellite Imagery: Strengths and Weaknesses." January 29, 2024. https://ivypanda.com/essays/satellite-imagery-strengths-and-weaknesses/.

Bibliography

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July 20, 2018

How satellites and other aerial technologies have changed society

by Peter Dizikes, Massachusetts Institute of Technology

Satellites have changed the way we experience the world, by beaming back images from around the globe and letting us explore the planet through online maps and other visuals. Such tools are so familiar today we often take them for granted.

Lisa Parks does not. A professor in MIT's Comparative Media Studies/Writing program, Parks is an expert on satellites and their cultural effects, among other forms of aerial technology. Her work analyzes how technology informs the content of our culture, from images of war zones to our idea of a "global village."

"I really wanted people to think of the satellite not only as this technology that's floating around out there in orbit, but as a machine that plays a structuring role in our everyday lives," Parks says.

As such, Parks thinks we often need to think more crisply about both the power and limitations of the technology. Satellite images helped reveal the presence of mass graves following the Srebrenica massacre in the 1990s Balkans war, for instance. But they became a form of "proof" only after careful follow-up reporting by journalists and other investigators who reconstructed what had happened. Satellites often offer hints about life on the ground, but not omniscience.

"Since satellite images are so abstract and remote, they necessitate closer scrutiny, re-viewing, careful description, and interpretation in ways that other images of war do not," Parks writes in her 2005 book "Cultures in Orbit."

Alternately, satellite images can open up our world—or be exclusionary. The landmark 1967 BBC show "Our World," one of the first broadcasts to feature live global satellite video links, was touted as a global celebration. But as Parks writes, it reinforced distinctions between regions, by emphasizing "the modernity, permanence, and civilizational processes of industrial nations," and thus "undermining the utopian assumption that satellites inevitably turned the world into a harmonic 'global village.'"

For her distinctive scholarship, Parks was hired by MIT in 2016. She studies a range of media technologies—from the content of television to drone imagery—and has co-edited five books of essays on such topics, including the 2017 volume "Life in the Age of Drone Warfare." Parks is also the principal investigator for MIT's Global Media Technologies and Cultures Lab, which conducts on-site research about media usage in a range of circumstances.

"Technology and culture is what I'm interested in," Parks says.

Big sky, then and now

Parks grew up in Southern California and Montana. Her father was a civil engineer and her mother was a social worker—a combination, Parks suggests, that may have helped shape her interests in the social effects of technology.

As an undergraduate at the University of Montana, Parks received her BA in political science and history. She initially expected to become a lawyer but then reconsidered her career path.

"I didn't want to be in an office all of the time," Parks says. So she went back to the classroom, at the University of Wisconsin at Madison, where she received her Ph.D. in media studies. It was there that Parks' attention really turned to the skies and the technologies orbiting in them. She wrote a research paper on satellites that turned into both her dissertation and first book. Parks then took a job at the University of California at Santa Barbara, where she taught for over a decade before joining MIT.

"I loved my job there, I loved working in the U.C. system, and I had excellent colleagues," says Parks. Still, she adds, she was fascinated by the opportunities MIT offers, including its abundant interdisciplinary projects that pull together researchers from multiple fields.

"MIT seems to really value those kinds of relationships," Parks says.

In the classroom, Parks teaches an undergraduate course on current debates in media, which grapples with topics ranging from surveillance to net neutrality and media conglomerations. For graduate students, she has been teaching a foundational media theory course.

"If you're an MIT student and you want to come out of this place having thought about some of the policy implications relating to the media in this current environment, our classes equip you to think historically and critically about media issues," Parks says.

Technology … and justice for all

One other issue strongly motivates Parks' scholarship: the idea that technology is unevenly distributed around the world, with important implications for inequality.

"Most people in the world live in relatively disenfranchised or underprivileged conditions," Parks says. "If we shift the question about designing technologies so they serve a broader array of people's interests, and designs are interwoven with concerns about equity, justice, and other democratic principles, don't those technologies start to look different?"

To this end, MIT's Global Media Technologies and Cultures Lab, under Parks' direction, studies topics such as media infrastructure, to see how video is distributed in places such as rural Zambia. Parks' research has also examined topics such as the video content accessible to Aboriginal Australians, who, starting in the 1980s, attempted to gain greater control of, and autonomy over, the satellite television programming in rural Australia.

Parks' research takes place in a variety of social and economic orbits: In March, you could have found her and a research assistant, Matt Graydon, at the Satellite 2018 convention in Washington, interviewing CEOs and industry leaders for a new study of satellite -based internet services.

In some places around the globe, the effects of aerial technology are more immediate. In the volume on drones, Parks writes that these tools create a "vertical mediation" between ground and sky—that when "drones are operating in an area over time, above a certain region, they change the status of sites and motions on the ground." She elaborates on this in her new book, out this year, "Rethinking Media Coverage: Vertical Mediation and the War on Terror."

As diverse as these topics may seem at first, Parks' scholarly output is intended to expore more deeply the connection between aerial and orbital technologies and life on the ground, even if it is not on the mental radar for most of us.

"We need to be studying these objects in orbit above, and think about orbital real estate as something that's relevant to life on Earth," Parks says.

Provided by Massachusetts Institute of Technology

This story is republished courtesy of MIT News ( web.mit.edu/newsoffice/ ), a popular site that covers news about MIT research, innovation and teaching.

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• Communication Systems
• Earths Satellites

Earth's Satellites

Projectile Nature of a Satellite Types of Satellites

What is a Satellite?

• An object orbiting around the sun, earth or any other colossal body is known as a satellite. There are two major types of categorization when it comes down to satellites, one is natural and the other is man-made.
• Some examples of natural satellites are planets, moons, and comets. Jupiter has 67 natural satellites. The earth has one permanent natural satellite, the moon we know, which causes the tides in the sea. Sometimes other objects (like asteroids) can enter into temporary orbits of the earth and become a natural satellite for a span.
• Apart from these, the earth has many man-made satellites that are placed in the orbit and are used for different applications in communications and information gathering. As the term itself states, an artificial satellite is one that is put in our space by human efforts and follows the orbit of natural satellites.
• Since they have a very large view field, they can collect data a lot faster than instruments that can be used at ground level. Apart from this, their view into space beyond earth is not blocked by clouds, dust, and other obscurities, due to which a satellite can view space a lot more efficiently than telescopes on earth.

• Currently, there are more than 2,500 man-made satellites orbiting the earth. Most of these are of Russian origin. You may wonder why none of these satellites collides with each other, considering the volume. Actually, it is quite possible for this to occur. Although care is taken to launch a satellite in specific orbits such that collisions never occur, these orbits can vary in nature. There are many international organizations in place to prevent such occurrences. However, in 2009, a couple of Russian and American satellites did collide for the first time!
• The satellites are launched with a specific objective in mind pertaining to several uses such as communications, research in scientific areas, forecasting the weather, and intelligence. Once out in the space, all the different types of satellites follow similar physics principles and are governed by the same math equations.

Based on their purpose, there are two kinds of artificial satellites. They are geostationary satellites and polar satellites.

Types of Satellites:

Geostationary satellite:, polar satellite:.

Polar satellites revolve around the earth in a north-south direction around the earth as opposed to east-west like the geostationary satellites. They are very useful in applications where the field vision of the entire earth is required in a single day. Since the entire earth moves below them, this can be done easily. They are used in weather applications where predicting weather and climate-based disasters can be done in a short time. They are also used as relay stations.

The International Space Station (ISS) was launched into orbit in 1998. It is a habitable artificial satellite and sometimes can be seen on nights with a clear sky. It functions as a lab, observatory, and a landing base for possible expeditions.

Projectile Nature of a Satellite:

• The main thing one can understand about a satellite is that at the end of the day, they are projectiles. Any object, that only has the force of gravity acting upon it, is known as a satellite. The gravity’s force is the only thing that affects a satellite once it is launched into the orbit.

• To understand this concept clearly, we will use the example of launching a satellite from the top of Newton’s Mountain which is a hypothetical location well above the influence of the drag force of the air. Newton was the first scientist to give the concept that if an object is launched with the adequate speed it will start orbiting the earth. This object would experience a gravitational pull that would try to pull it downwards when it travels in a horizontal direction tangentially to the earth.
• If the launch speed is slower than the escape velocity it will fall back to the earth. The lines A and B of the diagram represent those types of projectiles .
• If a projectile is shot off at an escape velocity with the perfect speed it will fall into an orbit outside the earth and will start revolving around the earth; the dotted line C represents such an object. If launched at a higher speed, the object will still revolve around the earth but will now have an elliptical orbit; the dotted line D represents such an object.
• It can also be possible that the object is shot at such a speed that it escapes the gravitational pull of the earth and become a free body; the solid line E represents such an object. The objects C and D never fall back to the earth even though being pulled towards it continuously, as our earth is a circular body.

The below video helps in understanding the concepts such as speed and time period of the satellite and also the circular motion:

Velocity Needed for an Object to Orbit the Earth in a Circular Pattern:

This entire observation raises a very basic question, that how much velocity is necessary for shooting a body out of the earth’s lower atmosphere and establishing it into the outer one still in the range of the gravitational force . We get the answer by observing the most basic aspect of the earth, measuring its curvature. It has been measured that for every 8000 meters that one goes along the horizon of the earth, the surface dips down by about 5 meters. Thus, applying basic mathematics we get the assumption that if a projectile wants to orbit around the sun, it will have to be at such a speed that it travels 8000 m for every 5 m of downward fall. It was observed that if an object is launched horizontally it will fall by around 5 meters in the first second. Thus, we get to the conclusion that an object that is launched with a velocity of around 8000 m/s will orbit the earth in a circular pattern. This is only applicable when the object experiences an insignificant amount of atmospheric drag. The launched object will travel at a speed of around 8000 meters in a second and will drop around 5 meters but as the earth is spherical and has a curvature that drops 5 meters every 8000 meters, the object will never touch the ground.

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satellite communication

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• Food and Agriculture Organization - Satellite Communications Systems
• The Canadian Encyclopedia - Satellite Communication
• CORE - Advanced Satellite Communications
• DigitalCommons@University of Nebraska - Lincoln - Legal aspects of satellite communications—A mini handbook
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satellite communication , in telecommunications , the use of artificial satellites to provide communication links between various points on Earth . Satellite communications play a vital role in the global telecommunications system. Approximately 2,000 artificial satellites orbiting Earth relay analog and digital signals carrying voice, video, and data to and from one or many locations worldwide.

Satellite communication has two main components: the ground segment, which consists of fixed or mobile transmission, reception, and ancillary equipment, and the space segment, which primarily is the satellite itself. A typical satellite link involves the transmission or uplinking of a signal from an Earth station to a satellite. The satellite then receives and amplifies the signal and retransmits it back to Earth, where it is received and reamplified by Earth stations and terminals. Satellite receivers on the ground include direct-to-home (DTH) satellite equipment, mobile reception equipment in aircraft, satellite telephones, and handheld devices.

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May 25, 1945: Sci-Fi Author Predicts Future by Inventing It

1945: Arthur C. Clarke begins privately circulating copies of a paper that proposes using space satellites for global communications.

It was a bold suggestion for 1945, as the war was just winding down and most people were undoubtedly more concerned about the necessities of life than they were with beaming radio waves down from space. But Clarke, a physicist and budding science-fiction author, had his head firmly in the future. The paper, "The Space-Station: Its Radio Applications," suggests that space stations could be used for broadcasting television signals (.pdf).

The Space-station was originally conceived as a refueling depot for ships leaving the Earth. As such it may fill an important though transient role in the conquest of space, during the period when chemical fuels are employed.... However, there is at least one purpose for which the station is ideally suited and indeed has no practical alternative. This is the provision of world-wide ultra-high-frequency radio services, including television.

(Television itself was barely a commercial reality at this point, so that's some forward thinking.)

Clarke followed up on this private paper with an article published in October 1945 in Wireless World titled, "Extra-Terrestrial Relays: Can Rocket Stations Give World-wide Radio Coverage?" The paper discusses how rocket technology, such as that used in German V-2s during the war, could be turned to peaceful ends by launching artificial satellites into orbit. All you needed, Clarke argued, was a rocket capable of pushing a payload past an orbital-insertion velocity of 8 km/second [5 miles/second].

However, the smallest orbits – such as those that would be used by the Russian Sputnik satellites in the following decade – would circle the earth in about 90 minutes. Because of basic orbital mechanics, the farther out you could get a satellite, the slower its orbit around the Earth would be. At one point, about 42,000 km [about 26,100 miles] from the center of the Earth, the satellite's orbit would be exactly 24 hours, the same as the Earth's rotation. Clarke wrote, in Wireless World :

A body in such an orbit, if its plane coincided with that of the earth's equator, would revolve with the earth and would thus be stationary above the same spot on the planet. It would remain fixed in the sky of a whole hemisphere and unlike all other heavenly bodies would neither rise nor set.

Clarke wasn't the first to propose such an orbit, known as geostationary , but his essay did popularize the idea. And while it may have seemed far-fetched in 1945, it was less than 12 years before Sputnik and only 17 years before the first TV broadcast satellite, Telstar . Then, in 1965, Intelsat began launching the first satellite system based on geostationary satellites, and there are more than 300 such satellites in Clarke orbits today. The future of communications evolved much as Clarke had foreseen it.

Although Clarke eventually became more famous as a science-fiction author, penning such classics as 2001 and Childhood's End, he regarded his satellite proposal as more significant. I interviewed Clarke for a profile in Mobile PC magazine's March 2004 issue. The headline referred to him as "The Father of the Star Child." He replied with this note, handwritten on a reprint of his original Wireless World story:

Appreciate the write-up in March ... but I think being 'father' of the COMSAT more important than the Star Child!

Source: Various

Image: Figure II from Arthur C. Clarke's May 25, 1945, paper "shows diagrammatically some of the specialised services that could be provided by the use of differing radiator systems. Programme from A being relayed to point B and area C. Programme from D being relayed to whole hemisphere."

See Also:- Video: Arthur C. Clarke’s Last Message to Earth

• Arthur C. Clarke: The Wired Words
• Behind the Scenes of a Satellite Launch
• Elevator to the Top: Space Elevators Climbing Towards Reality
• Jan. 25, 1945: Fluoridation
• Jan. 27, 1945: Nazi Hell on Earth
• Jan. 30, 1945: Torpedoed
• March 9, 1945: Burning the Heart Out of the Enemy
• March 19, 1945: Blow It All Up
• April 14, 1945: Tweaky Toilet Costs Skipper His Sub
• April 30, 1945: New Generation U-Boat Too Little, Too Late
• May 5, 1945: Japanese Balloon Bomb Kills 6 in Oregon
• July 16, 1945: Trinity Blast Opens Atomic Age
• Aug. 6, 1945: 'I Am Become Death, Destroyer of Worlds'
• Oct. 18, 1945: Red Spy Steals U.S. Atom Bomb Secrets
• May 25, 1961: JFK Vows to Put American on Moon by Decade's End
• May 25, 2001: Towel Day Honors Hitchhiker Author Adams

English Essay on “Artificial Satellites” Astronomy Essay, Paragraph, Speech for Class 6, 7, 8, 9, 10, 12 Exam.

Artificial satellites.

An artificial satellite is a manufactured object that continuously orbits Earth or some other body in space. Most artificial satellites orbit Earth. People use them to study the universe, help forecast the weather, transfer telephone calls over the oceans, assist in the navigation of ships and, aircraft, monitor crops and other resources, and support military activities.

Artificial satellites also have orbited the moon, the sun, asteroids, and the planets Venus, Mars, and Jupiter. Such satellites mainly gather information about the bodies they orbit.

Piloted spacecraft in orbit, such as space capsules, space shuttle orbiters, and space stations, are also considered artificial satellites.

So, too, are orbiting pieces of “space junk,” such as burned-out rocket boosters and empty fuel tanks that have not fallen to Earth. But this article does not deal with these kinds of artificial satellites.

Artificial satellites differ from natural satellites, natural objects that orbit a planet. Earth’s moon is a natural satellite. The Soviet Union launched the first artificial satellite, Sputnik 1, in 1957. Since then, the United States and about 40 other countries have developed, launched, and operated satellites. Today about 3000 useful satellites and 6,000 pieces of space junk are orbiting Erath.

Satellite orbits have a variety of shapes. Some are circular, while others are highly elliptical (egg-shaped). Orbits also vary in altitude. Some circular orbits, for example, are just above the atmosphere at an altitude of about 155 miles (250 kilometers), while others are more than 20,000 miles (32,200 kilometers) above Earth. The greater the altitude, the longer period — the time it takes a satellite to completer one orbit.

A satellite remains in orbit because of a balance between the satellite’s velocity (the speed at which it would travel in a straight line) and the gravitational force between the satellite and Earth. Were it not for the pull of gravity, a satellite’s velocity would send it flying away from Earth in a straight line. But were it not for velocity gravity would pull a satellite back to Earth.

To help understand the balance between gravity and ve consider what happens when a small weight has attached a lock to a string and swung in a circle. If the string were to break, the weight would fly off in a  line. like gravity, however, the string acts keeping the weight in its orbit. The weight and string can also show the relationship between a satellite’s altitude and its orbital period. A long string is like a high altitude. The weight takes a relatively long time to complete one circle. A short string is like a low altitude. The weight has a relatively short orbital period. orbital period.

Many types of orbits exist, but most artificial satellites orbiting Earth travel in one of four types:

(1) high altitude, geosynchronous,

(2) medium-altitude,

(3) un-synchronous, polar; and

(4) low altitude. Most orbits of these four types are circular.

A high altitude, geosynchronous orbit lies above the equator at an altitude of about 22,300 miles (35,900 kilometers). A satellite this orbit travels around Earth’s axis at exactly the same time, d in the same direction, as Earth rotates about its axis. Thus, as seen from Earth, the satellite always appears at the same place in the sky overhead. To boost a satellite into this orbit requires a large, powerful launch vehicle.

A medium-altitude orbit has an altitude of about 12,400 miles (20,000 kilometers) and an orbital period of 12 hours. The orbit is outside Earth’s atmosphere and is thus very stable. Radio signals sent from a satellite at medium altitudes can be received over a large area of Earth’s surface. The stability and wide coverage of the orbit make it ideal for navigation satellites.

A sun-synchronous, polar orbit has a fairly low altitude and passes almost directly over the North and South poles. A slow drift of the orbit’s position is coordinated with Earth’s movement around the sun in such a way that the satellite always crosses the equator at the same local time on Earth. Because the satellite flies over all latitudes, its instruments can gather information on almost the entire surface of Earth. One example of this type of orbit is that of the TERRA Earth Observing System’s NOAA-H satellite. This satellite studies how natural cycles and human activities affect Earth’s climate. The altitude of its orbit is 438 miles (705 kilometers), and the orbital period is 99 minutes. When the satellite crosses the equator, the local time is always either 10:30 a.m. or 10:30 p.m.

A low-altitude orbit is just above Earth’s atmosphere, where there is almost no air to cause drag on the spacecraft and reduce its speed. Less energy is required to launch a satellite into this type of orbit than into any other orbit. Satellites that point toward deep space and provide scientific information generally operate in this type of orbit. The Hubble Space Telescope, for example, operates at an altitude of about 380 miles (610 kilometers), with an orbital period of 97 minutes.

Artificial satellites are classified according to their mission. There are six main types of artificial satellites:

(1) scientific research,

(2) weather,

(3) communications,

(4) navigation,

(5) Earth-observing, and

(6) military.

Scientific research satellites gather data for scientific analysis. These satellites are usually designed to perform one of three kinds of missions. (1) Some gather information about the composition and effects of the space near Earth. They may be placed in any of various orbits, depending on the type of measurements they are to make. (2) Other satellites record changes in Earth and its atmosphere. Many of them travel in sun-synchronous, polar orbits. (3) Still others observe planets, stars, and other distant objects. Most of these satellites operate in low altitude orbits. Scientific research satellites also orbit other planets, the moon, and the sun.

Weather satellites help scientists study weather patterns and forecast the weather. Weather satellites observe the atmospheric conditions over large areas.

Some weather satellites travel in a sun-synchronous, polar orbit, from which they make close, detailed observations of weather over the entire Earth. Their instruments measure cloud cover, temperature, air pressure, precipitation, and the chemical composition of the atmosphere. Because these satellites always observe Earth at the same local time of day, scientists can easily compare weather data collected under constant sunlight conditions. The network of weather satellites in these orbits also functions as a search and rescue system. They are equipped to detect distress signals from all commercial, and many private, planes and ships.

Other weather satellites are placed in high-altitude, geosynchronous orbits. From these orbits, they can always observe weather activity over nearly half the surface of Earth at the same time. These satellites photograph changing cloud formations. They also produce infrared images, which show the amount of heat corning from Earth and the clouds.

Communications satellites serve as relay stations, receiving radio signals from one location and transmitting them to another. A communications satellite can relay several television programs or many thousands of telephone calls at once. Communications satellites are usually put in a high altitude, geosynchronous orbit over a ground station. A ground station has a large dish antenna for transmitting and receiving radio, signals. Sometimes, a group of low orbit communications satellites arranged in a network called a constellation, work together by relaying information to each other and to users on the ground. Countries and commercial organizations, such as television broadcasters and telephone companies, use these satellites continuously. Navigation satellites enable operators of aircraft, ships, and land vehicles anywhere on Earth to determine their locations with great accuracy. Hikers and other people on foot can also use satellites for this purpose. The satellites send out radio signals that are picked up by a computerized -receiver carried on a vehicle or held in the hand.

Navigation satellites operate in networks, and signals from a network can reach receivers anywhere on Earth. ‘file receiver calculates its distance from at least three satellites whose signals it has received. It uses this information to determine its location.

Earth-observing satellites are used to map and monitor our planet’s resources and ever-changing chemical life cycles. They follow sun-synchronoUs, polar orbits. Under constant, consistent illumination from the sun, they take pictures in different colors of visible light and non-visible radiation. Computers on Earth combine and analyze the pictures. Scientists Earth-observing satellites to locate mineral deposits, to determine the location and size of freshwater supplies, to identify sources of pollution and study its effects, and to detect the spread of disease in crops and forests.

Military satellites include weather, communications, navigation, and Earth-observing satellites used for military purposes. Some military satellites — often called “spy satellites” — can detect the launch of missiles, the course of ships at sea, and the movement of military equipment on the ground.

Every satellite carries special instruments that enable it to perform its mission. For example, a satellite that studies the universe has a telescope. A satellite that helps forecast the weather carries cameras to track the movement of clouds.

In addition to such mission-specific instruments, all satellites have basic subsystems, groups of devices that help the instruments work together and keep the satellite operating. For example, a power subsystem generates, stores, and distributes a satellite’s electric power. This subsystem may include panels of solar cells that gather energy from the sun. Command and data handling subsystems consist of computers that gather and process data from the instruments and execute commands from Erath.

A satellite’s instruments and subsystems are designed, built, and tested individually Workers install them on the satellite one at a time until the satellite is complete. Then the satellite is tested under conditions like those that the satellite will encounter during launch and while in space. If the satellite passes all tests, it is ready to be launched.

Launching the satellite: Space shuttles carry some satellites into` space, but most satellites are launched by rockets that fall into the ocean after their fuel is spent. Many satellites require minoi ustments of their orbit before they begin to perform their function. Built-in rockets called thrusters make these adjustments. Once a satellite is placed into a stable orbit, it can remain there for a long time without further adjustment.

Most satellites operate are directed from a control center o Earth. Computers and human operators at the control center monitor the satellite’s position, send instructions to its computers and retrieve information that the satellite has gathered. The control center communicates with the satellite by radio. Ground’ stations within the satellite’s range send and receive the radio signals.

A satellite does not usually receive constant direction from its control center. It is like an orbiting robot. It controls its solar panels to keep them pointed toward the sun and keeps its antennas ready to receive commands. Its instruments automatically collect information.

Satellites in a high altitude, geosynchronous orbit are always in contact with Earth. Ground stations can contact satellites in low orbits as often as 12 times a day. During each contact, the satellite transmits information and receives instructions. Each contact must be completed during the time the satellite passes overhead — about 10 minutes.

If some part of a satellite breaks down, but the satellite remains capable of doing useful work, the satellite owner usually will continue to operate it. In some cases, ground controllers can repair or reprogram the satellite. In rare instances, space shuttle, crews have retrieved and repaired satellites in space. If the satellite can no longer perform usefully and cannot be repaired or reprogrammed, operators from the control center will send a signal to shut it off.

A satellite remains in orbit until its velocity decreases and gravitational force pulls it down into a relatively dense part of the atmosphere. A satellite slows down due to the occasional impact of air molecules in the upper atmosphere and the gentle pressure of the sun’s energy. When the gravitational force pulls the satellite down far enough into the atmosphere, the satellite rapidly compresses the air in front of it. This air becomes so hot that most or all of the satellite burns up.

In 1955, the United States and the Soviet Union announced plans to launch artificial satellites. On Oct. 4, 1957, the Soviet Union launched Sputnik 1, the first artificial satellite. It circled Earth once every 96 minutes and transmitted radio signals that could be received on Earth. On Nov. 3, 1957, the Soviets launched a second satellite, Sputnik 2. It carried a dog named Laika, the first animal to soar in space. The United States launched its first satellite, Explorer 1, on Jan. 31, 1958, and its second, Vanguard 1, on March 17, 1958.

In August 1960, the United States launched the first communications satellite’ Echo I. This satellite reflected radio signals back to Earth. In April 1960, the first weather satellite, Tiros I, sent pictures of clouds to Earth. The U.S. Navy developed the first navigation satellites. The Transit 1B navigation satellite first orbited in April 1960. By 1965, more than 100 satellites were being placed in orbit each year.

Since the 1970s, scientists have created new and more effective satellite instruments and have made use of computers and miniature electronic technology in satellite design and construction. In addition, more nations and some private businesses have begun to purchase and operate satellites. By the early 2000s, more than 40 countries owned satellites, and nearly 3,000 satellites were operating in orbit.

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Sitsmamba for crop classification based on satellite image time series.

15 Sep 2024  ·  Xiaolei Qin , Xin Su , Liangpei Zhang · Edit social preview

Satellite image time series (SITS) data provides continuous observations over time, allowing for the tracking of vegetation changes and growth patterns throughout the seasons and years. Numerous deep learning (DL) approaches using SITS for crop classification have emerged recently, with the latest approaches adopting Transformer for SITS classification. However, the quadratic complexity of self-attention in Transformer poses challenges for classifying long time series. While the cutting-edge Mamba architecture has demonstrated strength in various domains, including remote sensing image interpretation, its capacity to learn temporal representations in SITS data remains unexplored. Moreover, the existing SITS classification methods often depend solely on crop labels as supervision signals, which fails to fully exploit the temporal information. In this paper, we proposed a Satellite Image Time Series Mamba (SITSMamba) method for crop classification based on remote sensing time series data. The proposed SITSMamba contains a spatial encoder based on Convolutional Neural Networks (CNN) and a Mamba-based temporal encoder. To exploit richer temporal information from SITS, we design two branches of decoder used for different tasks. The first branch is a crop Classification Branch (CBranch), which includes a ConvBlock to decode the feature to a crop map. The second branch is a SITS Reconstruction Branch that uses a Linear layer to transform the encoded feature to predict the original input values. Furthermore, we design a Positional Weight (PW) applied to the RBranch to help the model learn rich latent knowledge from SITS. We also design two weighting factors to control the balance of the two branches during training. The code of SITSMamba is available at: https://github.com/XiaoleiQinn/SITSMamba.

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