Rainfall-Rate Retrieval from a Spaceborne Radar: Comparison between Single-Frequency, Dual-Frequency, and Dual-Beam Techniques

Abstract

This paper investigates the performances achievable in the retrieval of rain-rate profile from a spaceborne radar operating at attenuated frequencies. Results obtained from three radar systems using relevant range-profiling algorithms to estimate rainfall rate are numerically simulated and compared. The three considered systems are a single-beam-single-frequency (SBSF) radar, a single-beam-dual-frequency (SBDF) radar, and a dual-beam-single-frequency (DBSF) radar or ?stereoradar.? In each case, the sampling of a typical model rain cell is performed and the data are analyzed according to the selected algorithm for rainfall retrieval. Three possible frequencies for the SRSF and DBSF radars (13.8, 24, and 35 GHz) and two frequency pairs for the SBDF radar (13.8?35 GHz and 13.8?24 GHz) are used. For obtaining objective comparisons, the three instruments are assumed to operate with an identical detection threshold, spatial resolutions, and power measurement accuracy. The main aspects investigated are the dynamical range of rain retrieval and the sensitivity to the measurement noise, to the drop-size distribution variability, and to nonuniform beam-filling effects. It is concluded that a dual-beam system operating at 24 GHz may be a good candidate for mapping precipitation from space allowing to use optimally the full complementarity of SBSF and DBSF algorithms: SBSF algorithm provides with efficient estimates in light (usually stratiform) and moderate rain, while DBSF algorithm is well adapted to the case of convective rain.