What is the definition of a sounder in the context of atmospheric instruments?
A. The AIRS instrument is a “remote sounder”. There are several different types, depending upon just what the instrument is designed to measure. AIRS is a passive remote sounder that performs a spectral analysis of the infrared and microwave radiation escaping from the top of the atmosphere to determine the vertical structure of the temperature and water vapor distribution within its field of view (FOV). The instrument scans the FOV in a direction orthogonal to the flight path of the satellite, so that it maps a swath approximately 2000 km wide centered upon the nadir with a spatial resolution of 50 km. As the spacecraft circles the Earth from pole-to-pole, the swath becomes a band which progresses in a westerly manner as the Earth rotates. In 12 hours the instrument maps out the entire globe (day and night). Here is a very simple description of how our instrument works. CO2 is a strongly absorbing gas in our atmosphere. We have 2378-channel infrared “radio receiver” on our satellite.
