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RAMMB: Regional and Mesoscale Meteorology Branch logo CIRA: Cooperative Institute for Research in the Atmosphere logo NESDIS: NOAA Environmental Satellite, Data, and Information Service logo

The GOES Imagers' IR Bands

Fig. 1a presents a high resolution atmospheric absorption spectrum and comparative blackbody curves for temperatures ranging from 200 K to 300 K. The spectrum was observed by a satellite-borne interferometer, over a region where the earth surface temperature was around 295 K. The spectrum shows the effect of various atmospheric gasses on what is observed at the top of the atmosphere. At 6.7 um notice that most of the radiance received by the sensor comes from very cold temperatures; this is because water vapor is a very active absorber in that portion of the spectrum, and thus any radiation reaching the sensor comes from emission of water vapor that is very high in the atmosphere.

Around the 10.7 um region, most of the energy radiated from the surface reachs the sensor, thus the term "atmospheric window" since the temperature measured is close to scene temperature. The window region around 12 um, especially out toward 12.8 um, is contaminated by low level water vapor, and thus is called the "dirty window." Notice the region around 4.0 um (detailed in Fig. 1b), this is another "atmospheric window" region, and it is "cleaner" than either 10.7 or 12.0 um, however, it is contaminated by solar reflection during daytime. It is the GOES imagers' spectral band that lies in this window region, 3.78 - 4.03 um, that is the focus of this tutorial.

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