Special sensor microwave/imager

Its successor, the Special Sensor Microwave Imager / Sounder (SSMIS), is an enhanced eleven-channel, eight-frequency system.

This results in a nominal swath width of 1394 km allowing frequent ground coverage, especially at higher latitudes.

All parts of the globe at latitudes greater than 58° are covered at least twice daily except for small unmeasured circular sectors of 2.4° about the poles.

The spin rate of the SSM/I provides a period of 1.9 sec during which the DMSP spacecraft sub-satellite point travels 12.5 km.

The resolution is determined by the Nyquist limit and the Earth surface's contribution of 3 dB bandwidth of the signal at a given frequency (see Table).

Concerns about the radiometer's performance over the full range of space environmental conditions led to the F8 instrument being switched off in early December 1987 to avoid overheating.

Analysis showed inadequate thermal shielding of the sensor's radiometers due to excessive heating at perihelion.

Before the F8 was decommissioned, it aided investigations into measuring passive microwaves at higher Earth incidence angles (i.e. > 51 degrees).