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Cooperative Research Program (CoRP) | Center for Satellite Applications and Research (STAR)

The GOES 3.9 um Tutorial Glossary

AVHRR -

Advanced Very High Resolution Radiometer, a 5-channel (4 infrared channels and 1 visible channel) instrument flown on board NOAA sun-synchronous polar-orbiting satellites.

band -

can refer to either a narrow spectral channel selected out of the electromagnetic spectrum, or to a larger portion of the spectrum.

blackbody -

a surface or body that absorbs all radiation incident upon it. Likewise, a blackbody has the maximum possible radiative emission for its given temperature.

channel -

a discrete portion of the spectrum measured by a satellite instrument, defined by a filter function (vs. wavelength). Satellite channels have a finite width, typically ranging from around 0.2 um in the visible to greater than 1.0 um in the infrared, or to greater than 10 um for sounder infrared channels.

emissivity -

also called emittance - the non-dimensional ratio of the radiance emitted from an object at a particular wavelength to the radiance that a blackbody would emit at that same temperature and wavelength. Thus a surface with an emissivity equal to 1.0 is a blackbody. All natural surfaces have emissivities less than 1.0, although most earth land surfaces have infrared emissivities between 0.9 and 1.0.

GOES -

Geostationary Operational Environmental Satellites, a series of satellites, in geosynchronous orbit, launched by the U.S. and operated by NOAA/NESDIS. There have been three generations of GOES satellites, starting with the SMS/GOES series in the mid-1970s. The most recent GOES satellites are GOES-8 and GOES-9, launched in 1994 and 1995, respectively.

geostationary -

sometimes called geosynchronous - a characteristic of a satellite orbit in which the satellite circles the globe, over the equator, in synchronization with the earth's rotation. These satellites have a period of 24 h, allowing images of the scene below the satellite to be taken continuously, with little or no perceived movement.

Imager -

as applied to GOES satellites: a 5-channel instrument designed to measure in the visible and the infrared portions of the electromagnetic spectrum, to provide operational images every 15 minutes over most of the U.S.

infrared -

the portion of the electromagnetic spectrum with wavelengths ranging from longer than visible radiation, starting around 0.7 um, to wavelengths shorter than those in the microwave portion of the spectrum. Satellite instruments typically measure infrared radiation between wavelengths of about 3 um and 20 um.

Kirchoff's Law -

the law that states that for objects in thermodynamic equilibrium (being characterized by a single temperature, or radiatively stable) the absorptivity equals the emissivity.

longwave -

when referring to the infrared portion of the electromagnetic spectrum, longwave is the region above about 10 um.

lookup table - or color table -

the enhancement (often using color) applied to satellite imagery, used to emphasize certain features that may be of interest.

medium wave -

when referring to the infrared portion of the electromagnetic spectrum, medium wave is the region between about 5 um and 10 um.

microwave -

the portion of the electromagnetic spectrum with much longer wavelengths than infrared radiation, typically above about 1 mm.

NEDR -

Noise Equivalent Delta Radiance, or noise equivalent radiance - the uncertainty in satellite measurements in terms of radiance units. The NEDR is usually a constant, regardless of the temperature of the scene being observed.

NEDT -

Noise Equivalent Delta Temperature, or noise equivalent temperature - the uncertainty in satellite measurements in terms of temperature units. The NEDT is a value which depends on the temperature of the scene being observed.

NESDIS -

the National Environmental Satellite, Data, and Information Service, the part of NOAA which operates U.S. weather satellites and provides satellite data services to other branches of NOAA and other branches of the government.

NOAA -

the National Oceanic and Atmospheric Administration, part of the U.S. Department of Commerce, responsible for monitoring and predicting the state of the oceans and the atmosphere. Also the name of the current series of polar-orbiting sun-synchronous weather satellites operated by NOAA.

Planck function -

a function named after Max Planck, which describes the blackbody radiative emission of a surface or body as a function of wavelength and temperature. The Planck radiance is a unique value for each wavelength and temperature.

polar-orbiting -

a characteristic of a satellite orbit that allows the satellite to circle the globe approximately over the poles of the earth. Polar-orbiting satellites have orbital inclinations, with respect to the equator, of close to 90 degrees. Typically, polar-orbiting weather satellites are also sun-synchronous.

radiance -

a conserved quantity of energy per unit area, per unit solid angle, and per unit of spectrum bandwidth. Radiances are measured by satellite instruments called radiometers or spectrometers, typically in units of mW / (m2.sr.cm-1), in the infrared portion of the spectrum or in units of W / (m2.sr.um), in the visible portion of the spectrum.

radiance temperature -

sometimes called brightness temperature, or blackbody temperature - the temperature measured by a satellite instrument, usually detected in terms of radiance, but converted into a temperature through the Planck function at a given wavelength.

resolution -

the size of the field-of-view (FOV) of a satellite picture element, as measured on the earth in kilometers. Resolution can have a second meaning: as the distance between the centers of adjacent picture elements. The two resolutions can be different, resulting in either overlap of individual FOVs, or gaps between them.

scene temperature -

the actual temperature of the scene being viewed. This temperature differs from the radiance temperature of the surface due to emissivity, reflectance, and atmospheric attenuation of the radiation.

shortwave -

when referring to the infrared portion of the electromagnetic spectrum, shortwave is the region below about 5 um.

Sounder -

as applied to GOES satellites: a 19-channel instrument designed to provide visible and infrared spectral radiances, used to vertically probe, or sound, the atmosphere. This is done by employing spectral bands with different amounts of atmospheric absorption, in order to measure temperatures and moisture at different depths in the atmosphere. Sounder data is typically available from GOES every hour, over the same locations.

sun-synchronous -

a characteristic of a satellite orbit that allows the satellite's path to precess, or rotate slowly in synchronization with the earth's revolution around the sun. Sun-synchronous satellites view the earth below at the same local time each pass; and, by necessity, are polar-orbiting, viewing the earth below during both a day-time and a night-time overpass, approximately 12 hours apart.

TIROS -

Television and InfraRed Observation Satellite - an old term used for the first polar-orbiting weather satellites. Currently, satellites in the series are called NOAA satellites.

visible -

the portion of the electromagnetic spectrum viewable by the naked eye, with wavelengths ranging from approximately 0.43 um to 0.69 um.