|
Military Space Radar.
Aerospace provides expert technical and acquisition support to the Space Radar Integrated Program, which is being designed to provide global persistent intelligence, surveillance, and reconnaissance to the Defense Department and intelligence organizations, including worldwide day-night/all-weather imagery, moving-target information, and 3-D radar-mapping data. The system will give decision makers the ability to simultaneously look deep into denied areas of interest, in multiple theaters, across all levels of conflict nonintrusively and without risk to personnel or resources.
Radar software design Microwave technology Radio frequency technology Information assurance Electronic engineering Satellite operations |
|
Scientific/Military satellites Q) What space surveillance systems do you have? Q) What space surveillance systems should you have? Q) What research and development has been done in this regard? Q) What research and development is further required? Q) What results are available? Q) Who around the world has advanced resources and products services in this context? Q) What types of scientific satellites and explorers have there been? Q) What scientific satellites and explorers are planned for the future? Q) How much does one scientific satellite cost? Q) What is a satellite's life span? Q) What happens to scientific satellites when they reach the end of their life? Q) How are names chosen for scientific satellites and explorers? Q) Is remote sensing always done using satellites? Q) Is there a difference between a Landsat satellite and a RADARSAT satellite? Q) What is the difference between an ACTIVE and a PASSIVE sensor? Q) How does radar work? Q) Is there one remote sensing satellite that is the best? Q) How high up are these satellites? Q) How many remote sensing satellites are there? Q) How do the remote sensing satellites "cover" the Earth? Q) How long does it take for a satellite to "cover" the Earth? Q) How is the satellite data sent from way up there, down to us? Q) How long does it take the data to reach Earth? Q) Why are some satellite images in black and white and others in colour? Q) Why do we get such strange colours in many of these satellite images? Q) Can sensors see underground or underwater? |
|
Satellites Not so long ago, satellites were exotic, top-secret devices. They were used primarily in a military capacity, for activities such as navigation and espionage. Now they are an essential part of our daily lives. We see and recognize their use in weather reports, television transmission by DIRECTV and the DISH Network, and everyday telephone calls. In many other instances, satellites play a background role that escapes our notice: What is a Satellite? A satellite is basically any object that revolves around a planet in a circular or elliptical path. The moon is Earth's original, natural satellite, and there are many manmade (artificial) satellites, usually closer to Earth. * The path a satellite follows is an orbit. In the orbit, the farthest point from Earth is the apogee, and the nearest point is the perigee. * Artificial satellites generally are not mass-produced. Most satellites are custom built to perform their intended functions. Exceptions include the GPS satellites (with over 20 copies in orbit) and the Iridium satellites (with over 60 copies in orbit). * Approximately 23,000 items of space junk -- objects large enough to track with radar that were inadvertently placed in orbit or have outlived their usefulness -- are floating above Earth. The actual number varies depending on which agency is counting. Payloads that go into the wrong orbit, satellites with run-down batteries, and leftover rocket boosters all contribute to the count. This online catalog of satellites has almost 26,000 entries! Although anything that is in orbit around Earth is technically a satellite, the term "satellite" is typically used to describe a useful object placed in orbit purposely to perform some specific mission or task. We commonly hear about weather satellites, communication satellites and scientific satellites. Whose Satellite Was the First to Orbit Earth? The Soviet Sputnik satellite was the first to orbit Earth, launched on October 4, 1957. Sputnik's transmissions died along with its battery after only three weeks, but its effects have been felt for decades. As a fifth-grader, I witnessed the stir caused by the launch of Sputnik. News reports showed that many people in the United States were embarrassed to see the Soviet Union achieving a scientific first, as well as frightened that a foreign country had placed something overhead (read these Sputnik stories). Soviet rocket development seemed well ahead of the United States' efforts. The push toward getting an American satellite into space started immediately. American schools and universities were soon stocked with new science books. One side effect that had a direct impact on many students like me was an increase in science homework, giving a personal dimension to the national wake-up call. Because of Soviet government secrecy at the time, no photographs were taken of this famous launch. Sputnik was a 23-inch (58-cm), 184-pound (83-kg) metal ball. Although it was a remarkable achievement, Sputnik's contents seem meager by today's standards: * Thermometer * Battery * Radio transmitter - changed the tone of its beeps to match temperature changes * Nitrogen gas - pressurized the interior of the satellite On the outside of Sputnik, four whip antennas transmitted on short-wave frequencies above and below what is today's Citizens Band (27 MHz). According to the Space Satellite Handbook, by Anthony R. Curtis: After 92 days, gravity took over and Sputnik burned in Earth's atmosphere. Thirty days after the Sputnik launch, the dog Laika orbited in a half-ton Sputnik satellite with an air supply for the dog. It burned in the atmosphere in April 1958. Sputnik is a good example of just how simple a satellite can be. As we will see later, today's satellites are generally far more complicated, but the basic idea is a straightforward one. How is a Satellite Launched into an Orbit? Photo courtesy Arianespace ARIANE 44L (four liquid strap-on boosters) at liftoff from French Guiana, October 1998 All satellites today get into orbit by riding on a rocket or by riding in the cargo bay of the Space Shuttle. Several countries and businesses have rocket launch capabilities, and satellites as large as several tons make it safely into orbit on a regular basis. For most satellite launches, the scheduled launch rocket is aimed straight up at first. This gets the rocket through the thickest part of the atmosphere most quickly and best minimizes fuel consumption. After a rocket launches straight up, the rocket control mechanism uses the inertial guidance system to calculate necessary adjustments to the rocket's nozzles to tilt the rocket to the course described in the flight plan. In most cases, the flight plan calls for the rocket to head east because Earth rotates to the east, giving the launch vehicle a free boost. The strength of this boost depends on the rotational velocity of Earth at the launch location. The boost is greatest at the equator, where the distance around Earth is greatest and so rotation is fastest. How big is the boost from an equatorial launch? To make a rough estimate, we can determine Earth's circumference by multiplying its diameter by pi (3.1416). The diameter of Earth is approximately 7,926 miles (12,753 km). Multiplying by pi yields a circumference of something like 24,900 miles (40,065 km). To travel around that circumference in 24 hours, a point on Earth's surface has to move at 1,038 mph (1,669 kph). A launch from Cape Canaveral, Florida, doesn't get as big a boost from Earth's rotational speed. The Kennedy Space Center's Launch Complex 39-A, one of its launch facilities, is located at 28 degrees 36 minutes 29.7014 seconds north latitude. The Earth's rotational speed there is about 894 mph (1,440 kph). The difference in Earth's surface speed between the equator and Kennedy Space Center, then, is about 144 mph (229 kph). (Note: The Earth is actually oblate -- fatter around the middle -- not a perfect sphere. For that reason, our estimate of Earth's circumference is a little small.) Considering that rockets can go thousands of miles per hour, you may wonder why a difference of only 144 mph would even matter. The answer is that rockets, together with their fuel and their payloads, are very heavy. For example, the February 11, 2000 lift-off of the Space Shuttle Endeavor with the Shuttle Radar Topography Mission required launching a total weight of 4,520,415 pounds (2,050,447 kg). It takes a huge amount of energy to accelerate such a mass to 144 mph, and therefore a significant amount of fuel. Launching from the equator makes a real difference. Once the rocket reaches extremely thin air, at about 120 miles (193 km) up, the rocket's navigational system fires small rockets, just enough to turn the launch vehicle into a horizontal position. The satellite is then released. At that point, rockets are fired again to ensure some separation between the launch vehicle and the satellite itself. Earth's escape velocity is much greater than what's required to place an Earth satellite in orbit. With satellites, the object is not to escape Earth's gravity, but to balance it. Orbital velocity is the velocity needed to achieve balance between gravity's pull on the satellite and the inertia of the satellite's motion -- the satellite's tendency to keep going. This is approximately 17,000 mph (27,359 kph) at an altitude of 150 miles (242 km). Without gravity, the satellite's inertia would carry it off into space. Even with gravity, if the intended satellite goes too fast, it will eventually fly away. On the other hand, if the satellite goes too slowly, gravity will pull it back to Earth. At the correct orbital velocity, gravity exactly balances the satellite's inertia, pulling down toward Earth's center just enough to keep the path of the satellite curving like Earth's curved surface, rather than flying off in a straight line (read this page for details on orbits). The orbital velocity of the satellite depends on its altitude above Earth. The nearer Earth, the faster the required orbital velocity. At an altitude of 124 miles (200 kilometers), the required orbital velocity is just over 17,000 mph (about 27,400 kph). To maintain an orbit that is 22,223 miles (35,786 km) above Earth, the satellite must orbit at a speed of about 7,000 mph (11,300 kph). That orbital speed and distance permits the satellite to make one revolution in 24 hours. Since Earth also rotates once in 24 hours, a satellite at 22,223 miles altitude stays in a fixed position relative to a point on Earth's surface. Because the satellite stays right over the same spot all the time, this kind of orbit is called "geostationary." Geostationary orbits are ideal for weather satellites and communications satellites. The moon has an altitude of about 240,000 miles (384,400 km), a velocity of about 2,300 mph (3,700 kph) and its orbit takes 27.322 days. (Note that the moon's orbital velocity is slower because it is farther from Earth than artificial satellites.) * To get a better feel for orbital velocities at different altitudes, check out NASA's orbital velocity calculator. * To learn more about orbits and other topics in space flight, check out JPL's Basics of Space Flight Learners' Workbook. * A detailed technical treatment of orbital mechanics can be found at this site. In general, the higher the orbit, the longer the satellite can stay in orbit. At lower altitudes, a satellite runs into traces of Earth's atmosphere, which creates drag. The drag causes the orbit to decay until the satellite falls back into the atmosphere and burns up. At higher altitudes, where the vacuum of space is nearly complete, there is almost no drag and a satellite can stay in orbit for centuries (take the moon as an example). Satellites usually start out in an orbit that is elliptical. The ground control station controls small onboard rocket motors to provide correction. The goal is to get the orbit as circular as possible. By firing a rocket when the orbit is at the apogee of its orbit (its most distant point from Earth), and applying thrust in the direction of the flight path, the perigee (lowest point from Earth) moves further out. The result is a more circular orbit. What is a Satellite Launch Window? A launch window is a particular period of time in which it will be easier to place the satellite in the orbit necessary to perform its intended function. With the Space Shuttle, an extremely important factor in choosing the launch window is the need to bring down the astronauts safely if something goes wrong. The astronauts must be able to reach a safe landing area where rescue personnel can be standing by. For other types of flights, including interplanetary exploration, the launch window must permit the flight to take the most efficient course to its very distant destination. If weather is bad or a malfunction occurs during a launch window, the flight must be postponed until the next launch window appropriate for the flight. If a satellite were launched at the wrong time of the day in perfect weather, the satellite could end up in an orbit that would not pass over any of its intended users. Timing is everything! What is Inside a Typical Satellite? Satellites come in all shapes and sizes and play a variety of roles. For example: * Weather satellites help meteorologists predict the weather or see what's happening at the moment. Typical weather satellites include the TIROS, COSMOS and GOES satellites. The satellites generally contain cameras that can return photos of Earth's weather, either from fixed geostationary positions or from polar orbits. * Communications satellites allow telephone and data conversations to be relayed through the satellite. Typical communications satellites include Telstar and Intelsat. The most important feature of a communications satellite is the transponder -- a radio that receives a conversation at one frequency and then amplifies it and retransmits it back to Earth on another frequency. A satellite normally contains hundreds or thousands of transponders. Communications satellites are usually geosynchronous. * Broadcast satellites broadcast television signals from one point to another (similar to communications satellites). * Scientific satellites perform a variety of scientific missions. The Hubble Space Telescope is the most famous scientific satellite, but there are many others looking at everything from sun spots to gamma rays. * Navigational satellites help ships and planes navigate. The most famous are the GPS NAVSTAR satellites. * Rescue satellites respond to radio distress signals (read this page for details). * Earth observation satellites observe the planet for changes in everything from temperature to forestation to ice-sheet coverage. The most famous are the LANDSAT series. * Military satellites are up there, but much of the actual application information remains secret. Intelligence-gathering possibilities using high-tech electronic and sophisticated photographic-equipment reconnaissance are endless. Applications may include: o Relaying encrypted communications o Nuclear monitoring o Observing enemy movements o Early warning of missile launches o Eavesdropping on terrestrial radio links o Radar imaging o Photography (using what are essentially large telescopes that take pictures of militarily interesting areas) Despite the significant differences between all of these satellites, they have several things in common. For example: * All of them have a metal or composite frame and body, usually known as the bus. The bus holds everything together in space and provides enough strength to survive the launch. * All of them have a source of power (usually solar cells) and batteries for storage. Arrays of solar cells provide power to charge rechargeable batteries. Newer designs include the use of fuel cells. Power on most satellites is precious and very limited. Nuclear power has been used on space probes to other planets (read this page for details). Power systems are constantly monitored, and data on power and all other onboard systems is sent to Earth stations in the form of telemetry signals. * All of them have an onboard computer to control and monitor the different systems. * All of them have a radio system and antenna. At the very least, most satellites have a radio transmitter/receiver so that the ground-control crew can request status information from the satellite and monitor its health. Many satellites can be controlled in various ways from the ground to do anything from change the orbit to reprogram the computer system. * All of them have an attitude control system. The ACS keeps the satellite pointed in the right direction. The Hubble Space Telescope has a very elaborate control system so that the telescope can point at the same position in space for hours or days at a time (despite the fact that the telescope travels at 17,000 mph/27,359 kph!). The system contains gyroscopes, accelerometers, a reaction wheel stabilization system, thrusters and a set of sensors that watch guide stars to determine position. What Are the Types of Satellite Orbits? There are three basic kinds of orbits, depending on the satellite's position relative to Earth's surface: * Geostationary orbits (also called geosynchronous or synchronous) are orbits in which the satellite is always positioned over the same spot on Earth. Many geostationary satellites are above a band along the equator, with an altitude of about 22,223 miles, or about a tenth of the distance to the Moon. The "satellite parking strip" area over the equator is becoming congested with several hundred television, weather and communication satellites! This congestion means each satellite must be precisely positioned to prevent its signals from interfering with an adjacent satellite's signals. Television, communications and weather satellites all use geostationary orbits. Geostationary orbits are why a DSS satellite TV dish is typically bolted in a fixed position. * The scheduled Space Shuttles use a much lower, asynchronous orbit, which means they pass overhead at different times of the day. Other satellites in asynchronous orbits average about 400 miles (644 km) in altitude. * In a polar orbit, the satellite generally flies at a low altitude and passes over the planet's poles on each revolution. The polar orbit remains fixed in space as Earth rotates inside the orbit. As a result, much of Earth passes under a satellite in a polar orbit. Because polar orbits achieve excellent coverage of the planet, they are often used for satellites that do mapping and photography. How Are Satellite Orbits Predicted? Special satellite software, available for personal computers, predicts satellite orbits. The software uses Keplerian data to forecast each orbit and shows when a satellite will be overhead. The latest "Keps" are available on the Internet for amateur radio satellites, too. Satellites use a variety of light-sensitive sensors to determine their position. The satellite transmits its position to the ground station. Satellite Altitudes Looking up from Earth, satellites are orbiting overhead in various bands of altitude. It's interesting to think of satellites in terms of how near or far they are from us. Proceeding roughly from the nearest to the farthest, here are the types of satellites whizzing around Earth: 80 to 1,200 miles - Asynchronous Orbits Photo courtesy USGS The island of Manhattan in New York City (Central Park at the top) Observation satellites, typically orbiting at altitudes from 300 to 600 miles (480 to 970 km), are used for tasks like photography. Observation satellites such as the Landsat 7 perform tasks such as: * Mapping * Ice and sand movement * Locating environmental situations (such as disappearing rainforests) * Locating mineral deposits * Finding crop problems Search-and-rescue satellites act as relay stations to rebroadcast emergency radio-beacon signals from a downed aircraft or ship in trouble. The Space Shuttle is the familiar manned satellite, usually with a fixed duration and number of orbits. Manned missions often have the task of repairing existing expensive satellites or building future space stations. Teledesic, with the financial backing of Bill Gates, promises broadband (high-speed) communications using many planned low Earth orbiting (LEO) satellites. 3,000 to 6,000 miles - Asynchronous Orbits Science satellites are sometimes in altitudes of 3,000 to 6,000 miles (4,800 to 9,700 km). They send their research data to Earth via radio telemetry signals. Scientific satellite applications include: * Researching plants and animals * Earth science, such as monitoring volcanoes * Tracking wildlife * Astronomy, using the Infrared Astronomy Satellite * Physics, by NASA's future study of microgravity and the current Ulysses Mission studying solar physics 6,000 to 12,000 miles - Asynchronous Orbits For navigation, the U.S. Department of Defense built the Global Positioning System, or GPS. The GPS uses satellites at altitudes of 6,000 to 12,000 miles to determine the exact location of the receiver. The GPS receiver may be located: * In a ship at sea * In another spacecraft * In an airplane * In an automobile * In your pocket As consumer prices for GPS receivers come down, the familiar paper map may face tough competition. No more getting lost leaving the rental car agency at an unfamiliar airport! * The U.S. military and the forces of allied nations used more than 9,000 GPS receivers during Operation Desert Storm. * The National Oceanic and Atmospheric Administration (NOAA) used GPS to measure the exact height of the Washington Monument. Advanced Communications Technology Satellite, launched in 1993, used multiple antennas for narrow-beam transmissions. 22,223 Miles - Geostationary Orbits Weather forecasts visually bombard us each day with images from weather satellites, typically 22,223 miles over the equator. You can directly receive many of the actual satellite images using radio receivers and special personal-computer software. Many countries use weather satellites for their weather forecasting and storm observations. Data, television, image and some telephone transmissions are routinely received and rebroadcast by communications satellites. Typical satellite telephone links have 550 to 650 milliseconds of round-trip delay that contribute to consumer dissatisfaction with this type of long-distance carrier. It takes the voice communications that long to travel all the way up to the satellite and back to Earth. The round-trip delay forces many to use telephone conversations via satellite only when no other links exist. Currently, voice over the Internet is experiencing a similar delay problem, but in this case due to digital compression and bandwidth limitations rather than distance. Communications satellites are essentially radio relay stations in space. Satellite dishes get smaller as satellites get more powerful transmitters with focused radio "footprints" and gain-type antennas. Subcarriers on these same satellites carry: How Much Do Satellites Cost? Satellite launches don't always go well, as shown by this story on failed launches in 1999. There is a great deal at stake. For example, this hurricane-watch satellite mission cost $290 million. This missile-warning satellite cost $682 million. Another important factor with satellites is the cost of the launch. According to this report, a satellite launch can cost anywhere between $50 million and $400 million. A shuttle mission pushes toward half a billion dollars (a shuttle mission could easily carry several satellites into orbit). You can see that building a satellite, getting it into orbit and then maintaining it from the ground control facility is a major financial endeavor! Major U.S. satellite firms include: * Hughes * Ball Aerospace & Technologies Corp. * Boeing * Lockheed Martin How Can I See an Overhead Satellite? This satellite tracking Web site shows how you can see a satellite overhead, thanks to the German Space Operations Center. You will need your coordinates for longitude and latitude, available from the USGS Mapping Information. * Satellite-tracking software is available for predicting orbit passes. Note the exact times. Scientific satellites and explorers * Q:What types of scientific satellites and explorers have there been? * Q:What scientific satellites and explorers are planned for the future? * Q:How much does one scientific satellite cost? * Q:What is a satellite's life span? * Q:What happens to scientific satellites when they reach the end of their life? * Q:How are names chosen for scientific satellites and explorers? What types of scientific satellites and explorers have there been? Satellites developed at ISAS are grouped into four categories according to their field of science. (1) Engineering experiment satellites to test new engineering technologies: examples of these are the TANSEI series, SAKIGAKE, HITEN, and REIMEI, a small high-performance science satellite. (2) Astronomy satellites that make a contribution to radio astronomy, solar physics, x-ray astronomy and infrared astronomy: examples include HALCA, HINODE, SUZAKU and AKARI. (3) Magnetospheric observation satellites for making observations of magnetosphere: examples include AKEBONO and GEOTAIL. (4) Explorers for lunar and planetary exploration: such as SUISEI, NOZOMI, HAYABUSA and KAGUYA. What scientific satellites and explorers are planned for the future? Plans have been drawn up for a Venus-explorer PLANET-C, a radio-astronomical satellite ASTRO-G, and a Mercury-explorer BepiColombo. How much does one scientific satellite cost? On ISAS's scientific satellite/explorer missions, the average cost of the scientific satellites was approximately 1.2 billion yen and the M-V rockets to launch them about 7 billion yen. In addition, other expenses are incurred such as those required for satellite operation and launch-site maintenance. What is a satellite's life span? Some satellites complete their missions after a few years. Of those with a longer life, the solar-observation satellite YOHKOH was in operation for about 12 and a half years, the x-ray astronomical satellite ASUKA was in operation for approximately 8 years, and HALCA was in operation for about 9 years. It has been about 15 and a half years since GEOTAIL was launched and over 19 years since AKEBONO was launched. They are both still in operation (as of February 2008). What happens to scientific satellites when they reach the end of their life? Satellites in low-earth orbit are forced to enter the atmosphere and are incinerated. Explorers are forced to collide with the targeted celestial body or left to continue traveling in space. How are names chosen for scientific satellites and explorers? Development codes are attributed to scientific satellites before launch in accordance with their type such as ASTRO-A, which means the first astronomy satellite. About one week before the scheduled launch, ballot boxes are set up at each center at the Uchinoura Space Center as well as wherever people involved in the mission are located. Based upon votes received, a naming committee decides upon a Japanese name after giving due consideration to various pertinent conditions. In recent times, naming of some satellites has been open to the public. A list of pre-launch (in parentheses) and post-launch satellite names is given below. OHSUMI; TANSEI (MS-T1); SHINSEI (MS-F2); DENPA (REXS); TANSEI 2 (MS-T2); TAIYO (SRATS); TANSEI 3 (MS-T3); KYOKKO (EXOS-A); JIKIKEN (EXOS-B); HAKUCHO (CORSA-b); TANSEI 4 (MS-T4); HINOTORI (ASTRO-A); TENMA (ASTRO-B); OHZORA (EXOS-C); SAKIGAKE (MS-T5); SUISEI (PLANET-A); GINGA (ASTRO-C); AKEBONO (EXOS-D); HITEN (MUSES-A); YOHKOH (SOLAR-A); ASCA (ASTRO-D); HALCA (MUSES-B); NOZOMI (PLANET-B); HAYABUSA (MUSES-C); SUZAKU (ASTRO-EII); REIMEI (INDEX); AKARI (ASTRO-F); HINODE (SOLAR-B); KAGUYA (SELENE) Frequently asked questions Previous (Why does remote sensing work so well?) Index (Table of contents) Next (Glossary of remote sensing terms) 1. Is remote sensing always done using satellites? No. Remote sensing is simply sensing things from a distance. You do "remote sensing" whenever you look, hear or smell. Remote sensing can be done for business and scientific research using helicopters, airplanes, rockets, or balloons. Even kites have been tried, but satellites are definitely the most popular platform for carrying remote sensing equipment. 2. Is there a difference between a Landsat satellite and a RADARSAT satellite? Yes. Landsat carries a "Thematic Mapper" scanner that uses the visible and infrared parts of the electromagnetic spectrum to make images. As humans, we can only see the visible light part of the spectrum (the colours of red, orange, yellow, green, blue and violet), but we can't see the infrared parts as Landsat can. RADARSAT, however, carries a radar instrument that uses the radar or microwave part of the spectrum to make images. We can't see that part of the spectrum either. These are the same microwaves that are used in many other ways such as in microwave ovens. 3. What is the difference between an ACTIVE and a PASSIVE sensor? A camera provides an excellent example of both passive and active sensors. It is the film of the camera that is the sensor. It records the light that is reflected from the object that is being photographed. If the illumination for the scene is coming not from the camera but from another source (say, the sun) then the camera is a PASSIVE sensor. On a cloudy day or inside a room or at night, there may not be enough light. When the camera also has to provide the illumination for the scene (using a flash) it becomes an ACTIVE sensor. 4. How does radar work? A short pulse of energy is sent out by the radar antenna at an angle, towards the ground. The pulse bounces off targets on the ground (houses, trees, grass, telephone poles, etc.) and some of the energy is reflected back to the antenna. This is called "backscatter". The more energy a target backscatters, the brighter it will be shown on the radar image. 5. Is there one remote sensing satellite that is the best? There is no "best". The best choice of satellite data depends upon the application. Some satellites (and the sensors they carry) are designed for looking at fine detail so that small targets can be imaged. Other satellites specialize in covering very large areas all at once, or perhaps in revisiting the same area often. Radar-carrying satellites are chosen for use at night, for penetrating clouds or for mapping special targets like ice. Other satellites carry sensors that are particularly good at imaging in colour, to help in the "spectral" identification of targets. 6. How high up are these satellites? The earth observation satellites such as Landsat and RADARSAT are about 900 km above the Earth. This is much higher than the international space station (about 200 km) but not as high as the communication satellites (in geostationary orbit) that are used for TV and telephone (about 32,000 km). 7. How many remote sensing satellites are there? Lots. RADARSAT is Canadian. Other satellites belong to different countries such as U.S., Europe, Japan, France and India. Private companies are now launching remote sensing satellites too, because they have realized that this technology is very useful and profitable. 8. How do the remote sensing satellites "cover" the Earth? The Earth Observation satellites move in a "near polar" orbit. As the Earth spins west to east beneath them, they orbit from the North Pole down to the South Pole, back up to the North Pole, etc., each time passing close to, but not exactly over the poles. These two motions (the satellite orbit and the rotation of the Earth) make it possible for them to see almost the entire surface of the Earth. 9. How long does it take for a satellite to "cover" the Earth? One Landsat satellite, which looks straight down, takes 16 days to cover the whole of the Earth's surface. The NOAA satellite, which also looks straight down but covers a much wider area takes much less time. The RADARSAT and SPOT sensors, on the other hand, can be steered to point at a sideways angle at a target area from several neighbouring orbits. In this way, in a limited fashion, it is possible to get daily views of an area for several days. 10. How is the satellite data sent from way up there, down to us? There are two receiving stations in Canada. One is in Gatineau, Quebec, the other in Prince Albert, Saskatchewan. Together these two receiving stations can pick up all the data transmitted by satellites passing over any part of Canada. Other ground stations have been set up around the world to similarly capture data from a variety of satellites when they are overhead. Most of the time the satellites re-transmit the data that they receive directly to the ground station below them, using radio waves. At other times when the satellite is not within line-of-sight of a receiving station, it will store the data on board temporarily, and then transmit to the ground station when it passes overhead. 11. How long does it take the data to reach Earth? The data is transmitted instantaneously (well . . . . to be accurate, it's transmitted at the speed of light). 12. Why are some satellite images in black and white and others in colour? Some sensors record images from just one part of the electromagnetic spectrum, showing the image in shades (usually 256) of grey making what's called a "black and white" image. This is how RADARSAT works. When an image is recorded simultaneously in several parts of the spectrum, then three of those spectral "bands" are shown as shades of red and green and blue. Landsat and SPOT images are often displayed this way. From those three primary additive colours, one can make any of the other colours such as orange, brown, turquoise, etc. That is also how your TV and your computer monitor work - when the three images in red, green and blue are superimposed on the screen, a full range of colour results. 13. Why do we get such strange colours in many of these satellite images? Remote sensing uses parts of the spectrum that people can't see by eye: infrared, ultraviolet, radar, etc. If we want to display (on a photo or a computer monitor) one or more of these bands, we must use one or more of the three primary colours that people can see: red, green and blue. Therefore, you could get some strange combinations, like: infrared information shown as blue, red information shown as green and green information shown as blue !! The resulting colours will be nothing like what we experience using just our eyes. 14. Can sensors .see. underground or underwater? Under very special circumstances (using long wave radar over an area that is extremely dry) it is possible to see a few metres into the ground. In Canada, where usually the ground has lots of moisture, we are limited to seeing what's on the surface only. Some of the visible wavelengths, like blue for instance, penetrate water quite well and if the water is clear, we can see down several metres. 15. What is a "spectral fingerprint"? It's a way to try to identify objects in a satellite image. By using many parts of the spectrum, including the visible colours and perhaps parts of the infrared band, we try to find how an object reflects light. The way that an object reflects different parts of the spectrum is its "spectral fingerprint". There are different spectral fingerprints for different kinds of trees, crops, soil, etc. r Remote Sensing http://www.ccrs.nrcan.gc.ca/resource/tutor/planet/4_2_e.php http://www.isas.ac.jp/e/faq/02.shtml How many satellites are in space that broadcast TV? 1 Military Military is comprised of the Army, Navy, Air Force, Marines and Coast Guard and co-ordinate with police, intelligence agencies, administration, Judiciary, Leadership. 1. Why did you decide to join the military? 2. What are the benefits of joining the military for you? 3. How much does ______ spend on the military? 4. What does the military do? 5. What kind of training does the military do? under DOD At certain place in world CRPF, Police, BSF, ITBP, etc Under Home Dept. |