- OLS (Operational Linescan System), is the primary sensor on each satellite. The OLS
instrument consists of two telescopes and a photomultiplier tube (PMT). The detectors
sweep back and forth in a "whiskbroom" fashion (a "flying spot design" is employed
- a subset of whiskbroom scanners). The continuous analog signal is sampled at a constant
rate so the Earth-located centers of each pixel are roughly equidistant, i.e., 0.5
km apart, 7,325 pixels are digitized in the cross-track direction.
- SSM/I (Special Sensor Microwave Imager). The SSM/I is a seven-channel, four-frequency,
linearly-polarized, passive microwave radiometer (a total-power instrument configuration)
which measures atmospheric, ocean, and terrain microwave brightness temperatures (similar
to NIMBUS-7 SMMR) which are converted into environmental parameters such as: sea surface
winds, rain rates, cloud water, precipitation, soil moisture, ice edge, and ice age.
SMM/I data is used to obtain synoptic maps of critical atmospheric, oceanographic
and selected land parameters on a global scale. The footprint of SSM/I data is a 1400
km swath (conical scan).
- SSM/T (Special Sensor Microwave Temperature Sounder). The SSM/T is a seven channel
passive microwave sounder consisting of a rotating 7 step antenna reflector (rotating
once every 32 seconds), a Dicke-switched seven channel radiometer, a digitizer, and
signal processor. It measures the Earth's surface and atmospheric emission in the
50 to 60 GHz oxygen band. The SMM/T is a cross-track nadir scanning radiometer having
a FOV of 14.4A?. At nominal altitude (833 km) the subtrack spatial resolution is an
approximate circle of 174 km diameter at nadir elongating to an ellipse of 305 x 313
km at the extreme viewing angles toward the limb. There are seven total cross-track
scan positions separated by 12A? with a maximum cross-track scan angle of 36A?. Swath
width = 1500 km (data coverage gap between successive orbits). The SSM/T is a step
and stare type sensor which dwells on each of the seven scene stations, then observes
a cold (3 K) reference,
followed by a warm (300 K) reference.
- SSM/T2 (Special Sensor Microwave Water Vapor Profiler-2). The instrument is a cross-track
scanning, five channel, passive total power microwave radiometer system which consists
of a single, self-contained module with a step-scan motion in the cross-track direction
of A? 40.5A?. The SSM/T2 scan mechanism is synchronized with the SSM/T so that the
beam cell patterns of the two sensors coincide. The observation rate is 7.5 scans/minute.
There are 28 observations (beam positions) per scan for each of the five channels,
with each observation having a spatial resolution of about 48 km. All five channels
have coincident centers. The swath width is about 1500 km.
- SSJ/4 (Precipitation Electron/Proton Spectrometer) Objective: Measurement of transfer
energy, mass, and momentum of charged particles through the magnetosphere-ionosphere
in the Earth's magnetic field. The instrument looks toward the satellite zenith. -
The SSJ/4 sensor consists of four electrostatic analyzers that record the flux of
precipitating ions or electrons at 20 fixed energy channels between 30 eV and 30 keV.
The curved plate detectors allow precipitating electrons and ions to enter through
an aperture of about 20 x 10 (FWHM). Electrons and ions of the selected energy are
deflected toward the target by an imposed electric field applied across the two plates.
The two low energy detectors consist of 10 channels centered at 34, 49, 71, 101, 150,
218, 320, 460, 670, and 960 eV. The high energy detector measures particles in 10
channels centered at 1.0, 1.4, 2.1, 3.0, 4.4, 6.5, 9.5, 14.0, 20.5 and 29.5 KeV. Each
detector integrates each
channel for 0.09 s from high energy channel to low. A complete cycle is sampled each
second. The primary sources of the particles precipitating into the upper atmosphere
are the northern and southern auroral zones.
- SSI/ES (Special Sensor Ionospheric Plasma Drift/Scintillation Monitor) Objective:
Measurement of the ambient electron density and temperatures, the ambient ion density,
and the average ion temperature and molecular weight at the DMSP orbital altitude.
The instrument consists of an electron sensor (Langmuir probe) and an ion sensor mounted
on a 2.5 meter boom. The ion sensor is a planar aperture, planar collector sensor
oriented to face the spacecraft velocity vector at all times. In addition to the Langmuir
probe and planar collector which make up the SSI/E, the SSI/ES has a plasma drift
meter and a scintillation meter.
- SSM (Special Sensor Magnetometer), a triaxial fluxgate magnetometer. The SSM measures
geomagnetic fluctuations associated with solar geophysical phenomena (i.e., ionospheric
currents flowing at high latitudes). In combination with the SSI/ES and the SSJ/4,
the SSM provides heating and electron density profiles in the high-latitude ionosphere.
SSM takes and reports 12 readings/s for the Y and Z axes. Only 10 readings of the
12 readings per second are reported for the X axis due to telemetry limitations. The
SSM's axes are aligned with the spacecraft's axes where X is downward and aligned
to local vertical within 0.01 degree, Y is parallel to the velocity vector for spacecraft
with ascending node in the afternoon/evening sector, and Z is away from the solar
panel and anti-parallel to the orbit normal vector.) The measurement range is A?65535
nT for each axis, with a one-bit resolution of 2 nT. Note: The magnetic field has
three sources: 1)
the magnetic field from the solid Earth, 2) the magnetic field from electrical currents
flowing in the ionosphere and magnetosphere, and 3) the magnetic field from the spacecraft.
Measurement of source 2 is the principal objective of the SSM, the measurement of
source 1 is a secondary objective, and measurement of source 3 is a nuisance which
is eliminated from the data as much as possible during data processing