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Instrument: SSU : Stratospheric Sounding Unit
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Description
The SSU, supplied by the United Kingdom Meteorological
Office, employs a selective absorption technique to make
measurements in three channels. The principles of its operation
are based on the Selective Chopper Radiometer (SCR) flown on
Nimbus-4 and, and the Pressure Modulation Radiometer (PMR) flown
on Nimbus-6.

The SSU makes use of the pressure modulation technique to
measure radiation emitted from carbon dioxide at the top of the
earth's atmosphere. A cell of carbon dioxide gas in the
instrument's optical path has its pressure changed (at about a 40
Hz rate) in a cyclic manner. The spectral characteristics of the
channel and, therefore, the height of the weighting function is
then determined by the pressure in the cell during the period of
integration. By using three cells filled at different pressures,
weighting functions peaking at three different heights can be
obtained.

The primary objective of the instrument is top obtain data
from which stratospheric (25-50 km) temperature profiles can be
determined. This instrument was used in conjunction with the
HIRS/2 and MSU to determine temperature profiles from the surface
to 50 km (see the sensor reference for TIROS OPER VERTICAL
SOUNDER).

SSU Characteristics:
PRESSURE OF
WEIGHTING
FUNCTION PEAK
CELL --------------
CHANNEL PRESSURE(mb) (mb) (km)
------- ---------- ---- ----
1 100 15 29
2 35 5 37
3 10 1.5 45
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Entry taken from:
Rao,P.K., S.J. Holmes, R.K. Anderson, J.S. Winston, P.E. Lehr,
Weather Satellites: Systems, Data, and Environmental
Applications, American Meteorological Society, Boston, 1990.
ISBN 0-933876-66-1
Colwell,R.N. (Editor-in-Chief), Manual of Remote Sensing: Second
Edition, Volume I, American Society of Photogrammetry, 1983.
Cornillon, A Guide to Environmental Satellite Data, University of
Rhode Island Marine Technical Report 79, 1982.

Additional information available at
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area4/aapp/ssu.html&a=420&b=1&c=400&d=400&e=0"