Exploiting Over-Land OceanSat-2 Scatterometer Observations to Capture Short-Period Time-Integrated Precipitation

Abstract

stimation of overland precipitation using observations from the radar and passive microwave radiometer sensors onboard the current Global Precipitation Measurement (GPM) and predecessor Tropical Rainfall Measuring Mission (TRMM) satellites is constrained by the underlying surface variability. The factors controlling the multichannel microwave surface emissivity and radar surface backscatter are related to surface properties such as soil type and vegetation properties that vary with location and time. Variability due to slowly varying seasonal changes can be considered when simulating radar reflectivities and radiometer equivalent blackbody brightness temperatures for use with precipitation retrieval algorithms. However, over certain surfaces, a more transient, dynamic surface change is manifested upon the onset of intermittent rain events. In these situations, a timely update of the surface state prior to each satellite overpass, together with knowledge of the associated variability in the emissivity and radar surface backscatter, may be useful to improve the performance of the overland precipitation retrieval algorithms. In this study, the potential for wide-swath surface backscatter observations from the Ku-band, dual-beam OceanSat-2 scatterometer (OSCAT) is examined as a surface reference for tracking previous-time precipitation. Over certain surfaces, it is shown that a time-change detection approach is useful to isolate the change in radar backscatter owing to previous 3-h rainfall accumulations from the more slowly varying background state. A practical use of this method would be the production of an ancillary previous-time precipitation map, which could be consulted by retrieval algorithms to select (or adjust the weighting of) candidate solutions that represent the most current surface conditions.