Digital Earth Emissivity Information System (DEEIS) - Instruments

Special Sensor Microwave Imager (SSMI)

The Special Sensor Microwave Imager (SSMI) is a seven-channel, four- frequency, linearly-polarized, passive microwave radiometric system that measures atmospheric, ocean, and terrain microwave brightness temperatures. First launched in June of 1987 onboard the Defense Meteorological Satellite Program (DMSP) F8 satellite, it is now flown abord the F10, F11, F12, F13, and F15 satellites also. It is in a sun-synchronous polar orbit at an altitude of about 830 km. The SSMI has a swath width of 1394 km. The instrument rotates continuously about an axis parallel to the local spacecraft vertical. It takes 4.22 msec at 85.5 GHz for the antenna beam to scan 12.5km in the cross-track direction. There are 8.44 msec between every sample in the three other frequencies.

illustration of SSMI instrument characteristics
Table 4.1: SSMI Antenna Beamwidths (S/N 002)
Channel
Frequency (GHz)		 Polarization
(V/H)		 IF Pass-Band
(MHz)		 Beamwidth° EFOV on Earth Surface
E-Plane IFOV H-Plane IFOV H-Plane EFOV Along-Track Track
19.35 V 10-250 1.86 1.87 1.93 69 km 43 km
19.35 H 10-250 1.88 1.87 1.93 69 km 43 km
22.235 V 10-250 1.60 1.65 1.83 60 km 40 km
37.0 V 100-1000 1.00 1.10 1.27 37 km 28 km
37.0 H 100-1000 1.00 1.10 1.31 37 km 29 km
85.5 V 100-1500 0.41 0.43 0.60 15 km 13 km
85.5 H 100-1500 0.42 0.45 0.60 15 km 13 km
Table 4.2: SSMI Beam Efficiencies (S/N 002)
Channel Frequency (GHz) Polarization (V/H) Antenna Sidelobe (%) Cross-Polarization (%) Feedhorn Spillover Factor Beam (%)
19.35 V 0.8 0.35 0.969 96.1
19.35 H 0.4 0.30 0.969 96.5
22.235 V 2.0 0.65 0.974 95.5
37.0 V 7.3 1.80 0.986 91.4
37.0 H 4.7 1.20 0.986 94.0
85.5 V 5.7 0.60 0.988 93.2
85.5 H 7.8 1.40 0.988 91.1

For this and more information regarding SSMI and its various sensors, please go to the NSIDC SSMI page and the Colorado State SSMI website.