2. Scan Geometry
The SSMI has a scanning mechanism that consists of a broad-band, corrugated,
offset parabolic reflector. This is the larger disc shaped object sitting
atop the sensor in figure 2. (Hit here to see
figure 2 again) The microwave reflector is an ellipse, 61 X 66 cm,
with a 45 degree down angle (nadir angle). The projection of the scan spot
, or 'shadow' on the earth will be an approximate 51 degree incidence angle
(See figures 5 and 6) . Of course, the sensor itself is strictly passive:
it merely receives upwelling radiation and detects it. No microwave signal
is sent out from the spacecraft. Thus, when one refers to the 'projection'
or 'shadow' of the antenna, one is merely referring to the area on the
earth that the sensor is truly 'looking' at. The sensor rotates at 31.6
revolutions per minute, with a 1.9 second period and sweeps a swath 1395
Advanced Microwave Sensors record weather data onboard DMSP.
This artist's conception shows an Aerojet Electro-Systems SSMI scanning
from a future DMSP Block 5D-3 satellite.
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