CFOSAT Rotating Fan‐Beam Scatterometer Backscatter Measurement Processing

Abstract

Abstract The China‐France Oceanography Satellite (CFOSAT) was successfully launched on October 29, 2018, which carries two innovative payloads, that is, the surface waves investigation and monitoring (SWIM) instrument and the rotating fan‐beam scatterometer (RFSCAT). CFOSAT scatterometer (CSCAT) is dedicated to the monitoring of sea surface wind vectors and climate studies, but also for the applications over land and polar regions. CSCAT employs a “rotating fan‐beam” design rather than “pencil‐beam” approach and “fixed fan‐beam” approach adopted by the scatterometers in orbit before. In this paper, the data processing approach of CSCAT is described. The geolocation reference mapping model is employed in CSCAT slice geolocation. In noise processing, CSCAT adopts the method of weighted least squares polynomial surface fitting to conduct noise correction factor estimation adaptively. The attitude cube algorithm used for X integral factor computation is developed to obtain precise backscatter coefficients based on the radar equation. Because of the interdependency of the CSCAT data processing and the hardware configuration and onboard signal processing of the instrument, the instrument module configuration and signal processing design are also analyzed and presented comprehensively. Especially, the influence and compensation of Doppler frequency are introduced. The backscatter coefficient accuracy is estimated on the Amazon forest, and the results show that the backscatter coefficient accuracy of CSCAT on 25 × 25 km grids is less than 0.5 dB except that the near end and far end of the beam are slightly higher. The statistical results show the wind retrieval results meet the CFOSAT mission requirements.

Keywords

• CFOSAT
• scatterometer
• onboard signal processing
• backscatter coefficient
• noise adaptive estimation
• measurement accuracy