Rain retrieval over land from X-band spaceborne synthetic aperture radar: a model study

Numerous studies conducted as part of the Tropical Rainfall Measurement Mission (TRMM) program have demonstrated the benefits of space-borne precipitation measurements. The NASA Global Precipitation Mission (GPM) is an outgrowth of TRMM that will provide improved precipitation measurements and extend those measurements to higher latitudes. GPM satellite will carry a microwave imager coupled with a dual-frequency radar at Ku and Ka band. The forthcoming GPM will seek data from a constellation of satellites to provide measurements of precipitation that expand the coverage provided by the well-instrumented core satellite. The concept of getting precipitation data from an ensemble of satellite microwave sensors, both passive and active, has recently renovated the issue of using Synthetic Aperture Radars at X band (X-SARs). The radar frequency at X band is not too far from Ku band and rainfall signatures are expected to be revealed by X-SARs measurements. The main scientific benefit that will accrue from the use of will be the measurement of precipitation over land where microwave radiometers have had limited success. X-SAR precipitation retrievals will be especially valuable over mountainous terrain where ground based radars are obstructed. The high spatial (~100m) resolution of those radars will provide new insights into the structure of precipitating clouds (Atlas and Moore, 1987; Moore et al., 1997; Melsheimer et al., 1998).