All meteorologists are intimately familiar with the visual and infra-red
data from such conventional satellites as the US NOAA TIROS, GOES series,
European METEOSAT, and Japanese GMS. The GOES, METEOSAT, and GMS are all
GEOSTATIONARY satellites: as they orbit the earth, they maintain same location
over the earth (or nadir ) at all times. They orbit directly over the equator,
and have a velocity that allows them to maintain the same nadir continuously.
This is a great advantage, since a person can readily put images from this
type of spacecraft together and form an animation (using a system like
McIdas), since it always has the same field of view (FOV).
By contrast, the NOAA-TIROS satellite roughly orbits the earth from the
North pole to the South pole about 14 times or so a day. The satellite
orbit is referred to as SUN-SYNCHRONOUS- meaning that the plane of the
satellite orbit maintains a constant angle with respect to a plane containing
the earth's rotational axis and a line drawn from the center of the earth
to the sun. While maintaining this orbit, the field of view continuously
changes. While an image animation is more difficult with this type of satellite,
much higher resolution imagery is obtained.
This discussion will focus on the Polar orbiting, Sun Synchronous satellites,
and in particular , a type of spacecraft of the US Department of Defense,
the Defense Meteorological Satellite Program (DMSP). Aboard DMSP spacecraft,
there are three microwave sensors: the Passive Microwave Temperature Sounder
(SSM/T or SSM/T-1), the Passive Microwave Temperature Sounder [Water Vapor]
2 (SSM/T-2), and the Special Sensor Microwave Imager (SSM/I or SSMI). The
SSM/T-1 and SSM/T-2 are primarily focused on the retrieval of temperatures
in the upper troposphere / lower stratosphere. The SSMI is focused on the
retrieval of microwave energy emitted from the surface of earth. The main
thrust of this paper is to discuss the SSMI and explain its functionality,
design, and applications. A brief overview of the DMSP satellite will be
provided, then a description of the SSMI will follow. Each of the sensor
attributes will be explained in some detail, followed by a look at the
environmental products that can be derived from the SSMI.
Go to the next section.
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