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Instrument Type: sounder, Operational Mode: crosstrack, Collection Type: step-scan, Other Information: The SSU consists of a single primary telescope with a 10 degree IFOV which is step-scanned perpendicular to the satellite subpoint track. Each scan line is composed of eight individual 4.0 second steps and requires a total of 32 seconds, including time for the mirror retrace. The 10 degree IFOV gives a resolution of 147 km at the satellite subpoint and the stepping produces an underlap between adjacent scan lines of approximately 62 km at nadir. A calibration sequence is initiated every 256 seconds (8 scans) during which the radiometer is in turn, stepped to a position to view unobstructed space and an internal blackbody at a known temperature.