Precipitation patterns over the southern oceans derived from TOPEX and TMR measurements

Although the knowledge of the patterns of spatial and temporal variability of oceanic precipitation is critical to understanding and predicting global climate changes, it was only recently that the first spaceborne rain radar was placed in orbit. Until then, only infrared or passive microwave sensors were used for synoptic measurement of rain over ocean areas. However, thermal infrared images have a coarse resolution and passive microwave radiometers are not very efficient at measuring heavy rain events. On the other hand, dual-frequency radar altimeters, like TOPEX, are a potentially abundant source of rainfall data. The differential attenuation of the radar signal by the rain at the two separated frequencies allows to detect rain events and estimate the rainfall rate over oceanic regions. In addition to the dual-frequency Ku/C band radar altimeter, the TOPEX/Poseidon satellite also carries onboard a three-frequency nadir looking microwave radiometer (TMR), which enable to find rainfall estimates from the simultaneous and collocated measurements made by these two remote sensors. The main purpose of this work was to evaluate the potential of the simultaneous use of the TOPEX radar altimeter and microwave radiometer to study the precipitation patterns and quantify the rainfall rate over the southern oceans (35° S - 60° S). This study was performed with satellite data collected during the first five years of the TOPEX/Poseidon mission (1992-1997). The results obtained through the combined use of radar altimeter and microwave radiometer data taken by the TOPEX satellite showed a reasonable agreement with the corresponding precipitation patterns derived from independent passive microwave imagery acquired by the special sensor microwave/imager (SSM/I) onboard DMSP satellites, indicating that dual-frequency altimetry, specially when combined with non-imaging microwave radiometry, represents a very useful source of rainfall data in the southern oceans.