Improved Spatial Mapping of Rainfall Events with Spaceborne SAR Imagery

The Seasat satellite acquired the first spaceborne synthetic-aperture radar (SAR) images of the earth´s surface, in 1978, at a frequency of 1.275 GHz (L-band) in a like-polarization mode at incidence angles of 23 ± 30. Although this may not be the optimum system configuration for radar remote sensing of soil moisture, interpretation of two Seasat images of Iowa demonstrates the sensitivity of microwave backscatter to soil moisture content. In both scenes, increased image brightness, which represents more radar backscatter, can be related to previous rainfall activity in the two areas. Comparison of these images with ground-based rainfall observations illustrates the increased spatial coverage of the rainfall event that can be obtained from the satellite SAR data. These data can then be color-enhanced by a digital computer to produce aesthetically pleasing output products for the user community. When the methodology for extracting accurate information about soil moisture status from radar data is developed, it will prove useful in a wide variety of agronomic and hydrological investigations.