Microwave Radiometer/Scatterometer/ Altimeter

Description

The objectives of this S193 Skylab experiment were (1) to provide the near-simultaneous measurement of the radar differential backscattering cross section and the passive microwave thermal emission of the land and ocean on a global scale, and (2) to provide engineering data for use in designing space radar altimeters. The S193 was useful in studying varying ocean surfaces, wave conditions, sea and lake ice, snow cover, seasonal vegetational changes, flooding, rainfall and soil types. The sensor generally operated over ocean and ground areas where ground truth data were available, but additional targets of opportunity, such as hurricanes and storms, were viewed when the opportunity arose. S193 incorporated a radiometer, a scatterometer, and a radar altimeter, all operating at the same frequency of 13.9 GHz. The equipment shared a common gimballed antenna mounted on the outside of the multiple docking adapter. The scatterometer measured the backscattering coefficient of ocean and terrain as a function of incidence angle ranging from 0 to 48 deg. The radiometer was a passive sensor which measured the brightness temperature, from a cell on the earth's surface, as a function of incidence angle from the surface. The altimeter was a compressed-pulse radar system to measure average ocean-surface elevation variations with a resolution of about 0.9 km. The S193 ground coverage was 48 deg forward and 48 deg to either side of the spacecraft ground track. All data were recorded on magnetic tape on one digitized channel. The radiometer/scatterometer data were recorded at 5.33 kbs, the altimeter data at 10 kbs. For information of data availability, contact the EROS Data Center, U.S. Geological Survey, Sioux Falls, South Dakota.