A satellite ground track or satellite ground trace is the path on the surface of a planet directly below a satellite 's trajectory . It is also known as a suborbital track or subsatellite track , and is the vertical projection of the satellite's orbit onto the surface of the Earth (or whatever body the satellite is orbiting). A satellite ground track may be thought of as a path along the Earth's surface that traces the movement of an imaginary line between the satellite and the center of the Earth. In other words, the ground track is the set of points at which the satellite will pass directly overhead, or cross the zenith , in the frame of reference of a ground observer.
32-572: AIRS may refer to: Atmospheric Infrared Sounder , a weather and climate instrument flying on NASA's Aqua satellite Advanced Inertial Reference Sphere , a guidance system designed for use in the LGM-118A Peacekeeper ICBM Put on airs , a phrase describing a person who behaves as if they are better than other people Airable Internet Radio Service See also [ edit ] Air (disambiguation) Topics referred to by
64-402: A repeat ground track orbit with stable (minimally time-varying) orbit elements. These orbits use the nodal precession effect to shift the orbit so the ground track coincides with that of a previous orbit, so that this essentially balances out the offset in the revolution of the orbited body. The longitudinal rotation after a certain period of time of a planet is given by: where The effect of
96-457: A satellite can take a number of different forms, depending on the values of the orbital elements , parameters that define the size, shape, and orientation of the satellite's orbit, although identification of the always reliant upon the recognition of the physical form that is in motion; This was emphasised during speculation over the Vela incident , whereby identification of the matter in question
128-399: A single orbit, as in the geosynchronous and Molniya orbits discussed below. A satellite whose orbital period is an integer fraction of a day (e.g., 24 hours, 12 hours, 8 hours, etc.) will follow roughly the same ground track every day. This ground track is shifted east or west depending on the longitude of the ascending node , which can vary over time due to perturbations of the orbit. If
160-428: A wall to the infrared energy measured by AIRS. However, microwave instruments on board Aqua can see through the clouds with limited accuracy. Using a special computer algorithm , data from AIRS and the microwave instruments are combined to provide highly accurate measurements in all cloud conditions resulting in a daily global snapshot of the state of the atmosphere. AIRS and its companion microwave sounder AMSU observe
192-434: Is different from Wikidata All article disambiguation pages All disambiguation pages Atmospheric Infrared Sounder The atmospheric infrared sounder ( AIRS ) is one of six instruments flying on board NASA's Aqua satellite , launched on May 4, 2002. The instrument is designed to support climate research and improve weather forecasting . Working in combination with its partner microwave instrument,
224-428: Is said to be in a retrograde orbit . A satellite in a direct orbit with an orbital period less than one day will tend to move from west to east along its ground track. This is called "apparent direct" motion. A satellite in a direct orbit with an orbital period greater than one day will tend to move from east to west along its ground track, in what is called "apparent retrograde" motion. This effect occurs because
256-470: Is sensitive to temperature and water vapor over a range of heights in the atmosphere , from the surface up into the stratosphere . By having multiple infrared detectors, each sensing a particular wavelength, a temperature profile, or sounding of the atmosphere, can be made. While prior space instruments had only 15 detectors, AIRS has 2378. This greatly improves the accuracy, making it comparable to measurements made by weather balloons . Thick clouds act like
288-499: Is transported. The instrument also gives scientists their best view of atmospheric ozone in the Antarctic region during the polar winter. AIRS is also able to identify concentrations of sulphur dioxide and dust. [REDACTED] This article incorporates public domain material from How Airs Works . National Aeronautics and Space Administration . (and other articles). Ground track The ground track of
320-563: The Advanced Microwave Sounding Unit (AMSU-A), AIRS observes the global water and energy cycles, climate variation and trends, and the response of the climate system to increased greenhouse gases . AIRS uses infrared technology to create three-dimensional maps of air and surface temperature, water vapor , and cloud properties. AIRS can also measure trace greenhouse gases such as ozone , carbon monoxide , carbon dioxide , and methane . AIRS and AMSU-A share
352-407: The orbital nodes .) If the argument of perigee is non-zero, however, the satellite will behave differently in the northern and southern hemispheres. The Molniya orbit , with an argument of perigee near −90°, is an example of such a case. In a Molniya orbit, apogee occurs at a high latitude (63°), and the orbit is highly eccentric ( e = 0.72). This causes the satellite to "hover" over a region of
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#1732773048983384-469: The "nodes" (the points at which it crosses the equator ) will become closer together until at geosynchronous orbit they lie directly on top of each other. For orbital periods longer than the Earth's rotational period, an increase in the orbital period corresponds to a longitudinal stretching out of the (apparent retrograde) ground track. A satellite whose orbital period is equal to the rotational period of
416-728: The Aqua satellite with the Moderate Resolution Imaging Spectroradiometer ( MODIS ), Clouds and the Earth's Radiant Energy System (CERES), and the Advanced Microwave Scanning Radiometer-EOS (AMSR-E). Aqua is part of NASA's " A-train ," a series of high-inclination, Sun-synchronous satellites in low Earth orbit designed to make long-term global observations of the land surface, biosphere , solid Earth, atmosphere , and ocean. AIRS data are free and available to
448-414: The Earth is said to be in a geosynchronous orbit . Its ground track will have a "figure eight" shape over a fixed location on the Earth, crossing the equator twice each day. It will track eastward when it is on the part of its orbit closest to perigee , and westward when it is closest to apogee . A special case of the geosynchronous orbit, the geostationary orbit , has an eccentricity of zero (meaning
480-444: The Earth's rotation. The desire for equatorial launch sites, coupled with geopolitical and logistical realities, has fostered the development of floating launch platforms, most notably Sea Launch . If the argument of perigee is zero, meaning that perigee and apogee lie in the equatorial plane, then the ground track of the satellite will appear the same above and below the equator (i.e., it will exhibit 180° rotational symmetry about
512-437: The atmosphere to increased greenhouse gases. The instrument can detect carbon monoxide emissions from the burning of plant materials and animal waste by humans in rainforests and large cities. It can follow giant plumes of this gas moving across the planet from these large burns, allowing scientists to better monitor pollution transport patterns. AIRS provides a global daily 3-D view of Earth's ozone layer , showing how ozone
544-446: The atmosphere. Its scan mirror rotates around an axis along the line of flight and directs infrared energy from the Earth into the instrument. As the spacecraft moves along, this mirror sweeps the ground creating a scan swath that extends roughly 800 kilometers on either side of the ground track . Within the instrument, an advanced, high-resolution spectrometer separates the infrared energy into wavelengths . Each infrared wavelength
576-407: The concentration of carbon dioxide and methane globally. Its ability to provide simultaneous observations of the Earth's atmospheric temperature, water vapor, ocean surface temperature, and land surface temperature and infrared spectral emissivity, as well as humidity, clouds and the distribution of greenhouse gases, makes AIRS/AMSU a very useful space instrument to observe and study the response of
608-427: The entire Pacific Ocean, once in the morning and once in the evening. AIRS measurements form a "fingerprint" of the state of the atmosphere for a given time and place that can be used as a climate data record for future generations. They have become important tools for understanding current climate and increasing the ability to predict the future. Atmospheric Composition, Greenhouse Gases, and Air Quality AIRS maps
640-561: The entire atmospheric column from Earth's surface to the top of the atmosphere. The primary data they return is the infrared spectrum in 2378 individual frequencies. The infrared spectrum is rich in information on numerous gases in the atmosphere. AIRS primary scientific achievement has been to improve weather prediction and provide new information on the water and energy cycle. The instrument also yields information on several important greenhouse gases . Weather and climate forecasting AIRS data are used by weather forecasting centers around
672-417: The fact that the Earth is rotating about its own center of mass at the same rate as the satellite is orbiting. Orbital inclination is the angle formed between the plane of an orbit and the equatorial plane of the Earth. The geographic latitudes covered by the ground track will range from –i to i , where i is the orbital inclination. In other words, the greater the inclination of a satellite's orbit,
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#1732773048983704-533: The further north and south its ground track will pass. A satellite with an inclination of exactly 90° is said to be in a polar orbit , meaning it passes over the Earth's north and south poles . Launch sites at lower latitudes are often preferred partly for the flexibility they allow in orbital inclination; the initial inclination of an orbit is constrained to be greater than or equal to the launch latitude. Vehicles launched from Cape Canaveral , for instance, will have an initial orbital inclination of at least 28°27′,
736-506: The latitude of the launch site—and to achieve this minimum requires launching with a due east azimuth , which may not always be feasible given other launch constraints. At the extremes, a launch site located on the equator can launch directly into any desired inclination, while a hypothetical launch site at the north or south pole would only be able to launch into polar orbits. (While it is possible to perform an orbital inclination change maneuver once on orbit, such maneuvers are typically among
768-401: The most costly, in terms of fuel, of all orbital maneuvers, and are typically avoided or minimized to the extent possible.) In addition to providing for a wider range of initial orbit inclinations, low-latitude launch sites offer the benefit of requiring less energy to make orbit (at least for prograde orbits, which comprise the vast majority of launches), due to the initial velocity provided by
800-500: The northern hemisphere for a long time, while spending very little time over the southern hemisphere. This phenomenon is known as "apogee dwell", and is desirable for communications for high latitude regions. As orbital operations are often required to monitor a specific location on Earth, orbits that cover the same ground track periodically are often used. On earth, these orbits are commonly referred to as Earth-repeat orbits, and are often designed with "frozen orbit" parameters to achieve
832-466: The orbit is circular), and an inclination of zero in the Earth-Centered, Earth-Fixed coordinate system (meaning the orbital plane is not tilted relative to the Earth's equator). The "ground track" in this case consists of a single point on the Earth's equator, above which the satellite sits at all times. Note that the satellite is still orbiting the Earth — its apparent lack of motion is due to
864-515: The period of the satellite is slightly longer than an integer fraction of a day, the ground track will shift west over time; if it is slightly shorter, the ground track will shift east. As the orbital period of a satellite increases, approaching the rotational period of the Earth (in other words, as its average orbital speed slows towards the rotational speed of the Earth), its sinusoidal ground track will become compressed longitudinally, meaning that
896-725: The public through the Goddard Earth Sciences Data Information and Services Center. NASA's Jet Propulsion Laboratory in Pasadena, California, manages AIRS for NASA's Science Mission Directorate in Washington, D.C. The term "sounder" in AIRS's name refers to the fact that the instrument measures temperature and water vapor as a function of height ( atmospheric sounding ). AIRS measures the infrared brightness coming up from Earth's surface and from
928-405: The same term [REDACTED] This disambiguation page lists articles associated with the title AIRS . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=AIRS&oldid=1229577235 " Category : Disambiguation pages Hidden categories: Short description
960-509: The satellite orbits more slowly than the speed at which the Earth rotates beneath it. Any satellite in a true retrograde orbit will always move from east to west along its ground track, regardless of the length of its orbital period. Because a satellite in an eccentric orbit moves faster near perigee and slower near apogee, it is possible for a satellite to track eastward during part of its orbit and westward during another part. This phenomenon allows for ground tracks that cross over themselves in
992-406: The world. By incorporating AIRS measurements into their models , forecasters have been able to extend reliable mid-range weather forecasts by more than six hours. AIRS data have also improved forecasts of the location and magnitude of predicted storms. AIRS temperature and water vapor profiles are available in real time to regional weather forecasters, providing twice-daily weather measurements for
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1024-414: Was subject to numerous theories. Typically, satellites have a roughly sinusoidal ground track. A satellite with an orbital inclination between zero and ninety degrees is said to be in what is called a direct or prograde orbit , meaning that it orbits in the same direction as the planet's rotation. A satellite with an orbital inclination between 90° and 180° (or, equivalently, between 0° and −90°)
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