Glossary of Terms and Acronyms

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For data reception from geostationary satellites, a fixed-dish antenna is used; that is, the dish is aligned at the initial antenna setup to point at the geostationary satellite and then remains pointed in that same direction.  This is because the geostationary satellite maintains a constant position relative to the surface of the Earth.  Reception of the high-resolution data from the geostationary satellites (GVAR, PDUS, SVISSR) requires a large antenna dish (3.8m is the dish size used on TeraScan systems).

For data reception from polar-orbiting satellites, a tracking antenna is used, that is, the reception surface of the antenna (either a parabolic dish or a flat plate) moves to follow the satellite as it passes over the reception site in its orbit around the Earth.  The specific type of tracking antenna on a system depends on the telemetry to be received.   Most of the antennas have parabolic dishes, but two small antennas in use with some TeraScan systems have flat-plate reception surfaces.  The size of the receiving surface on the antenna is determined by the data rate in the telemetry to be received-- the higher the data rate, the larger the antenna dish required.

WEFAX from geostationary satellites can be received on the same tracking antennas used for L-band or S-band reception from polar-orbiting satellites.

The basic components of the antenna are:  (1) a parabolic dish or flat-plate reception surface; (2) a three-stage RF electronics assembly, including a feed, LNA, and downconverter, and (3) the mechanics and electronics for moving the antenna dish or plate, which, on an antenna used for tracking polar-orbiting satellites, is called the tracking positioner.

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The telemetry of this satellite is called SVISSR (stands for Stretched VISSR) The sensor on this satellite is an imager called VISSR   Link to info about GMS sensors.

The telemetry of these satellites is called GVAR.  The sensors of these satellites are the Imager and the Sounder.  Link to info about GOES sensors.

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An imager is a sensor carried on a satellite whose purpose is to scan the Earth below it, collecting electromagnetic (EM) radiation that can be used to produce a 2-D image of the scanned scene.  The imager scans across the Earth scene below it, producing a line of samples on each sweep.  Successive scan lines add together to form a swath of data from which an image is derived.  This swath of data is often referred to in the TeraScan community as a "pass".  

Imagers are designed for collecting specific wavelengths of EM radiation and most collect radiation in several bandwidths.  Each specific bandwidth of radiation collected is referred to as a channel.  Most imagers are passive sensors since they merely collect whatever radiation is reflected or emitted from the scene.  Examples of passive imagers are the HIRS, which collects IR radiation, and the AVHRR, which collects radiation in the visible, IR, and near-IR ranges of the EM spectrum.  The visible light (reflected sunlight) is used to make daylight images of the Earth's surface and atmosphere.  City lights and firelight can also be detected by visible channels at night.  IR images show variations in temperature of the scene being scanned.  IR radiation is used to produce nighttime images.

An imager that uses radar, such as the SAR, is called an active sensor because it sends out microwaves and measures the backscatter returned from the scene being so "illuminated". Objects that have rough surfaces or many edges result in more backscatter and appear brighter in an image.  Smooth surfaces, e.g., roads, appear black because the backscatter from them is minimal.

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The current schedule for subsequent launches is:
NOAA-M:  August 2001
NOAA-N:  June 2004
NOAA-N':  March 2008.  

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        oblique stereographic
        rectangular
        mercator
        universal trans mercator
        polyconic
        polar stereographic

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Synthetic Aperture Radar, sensor carried on the Radarsat-1.

SAR is also the name given to the telemetry of the ERS-2 and the Radarsat-1.

(n)  The data-reception schedule that results from the autoschedule record(s) defined in TeraCapCon.  The schedule can be viewed in TeraCapCon or by using the TeraScan command listsched or llsched.  The reception schedule gets automatically updated on a periodic basis (usually once a day just before 00:00 GMT). 

Except for the instruments of the DCS which collect radio signals from various platforms on Earth, most sensors on meteorological/environmental satellites are either imagers or sounders.  

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The imager on Meteosat-7 has three channels: one for visible radiation, one for infrared radiation, and one for water vapor.  For more, go to Meteosat VISSR

The imager on the GMS satellite has four channels: one for visible radiation, two for infrared radiation, and one for water vapor.  For more, go to GMS VISSR

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Last Update: $Date: 2002/02/08 21:42:50 $