Analysis of rain effects on China-France oceanography satellite scatterometer backscatter measurements

• Published in: Remote sensing letters 2024-10, Vol.15 (10), p.1011-1022
• Main Authors: Quan, Meixuan, Yan, Qiushuang, Fan, Chenqing, Meng, Junmin, Zhang, Jie
• Format: Article
• Language: English
• Subjects: Anisotropy; Atmospheric precipitations; Backscatter; Backscatter coefficient; Backscattering; CFOSAT scatterometer; Data analysis; Incidence angle; ocean surface wind; Oceanography; Polarization; Radar; Radar cross sections; Rain; rain effect; Satellite observation; Satellites; Scatterometers; Sensitivity; Weather forecasting; Wind; Wind effects; Wind speed
• ISSN: 2150-704X; 2150-7058
• DOI: 10.1080/2150704X.2024.2399328

The rotating fan beam scanning observation mechanism of China-France oceanography satellite (CFOSAT) scatterometer provides more comprehensive ocean measurements. However, its data quality is often impacted by rain contamination. In this study, we analysed the effect of rain on CFOSAT SCATterometer (CSCAT) backscatter measurements by collocating CSCAT data, the Integrated Multi-satellitE Retrievals (IMERG) rain data, and the wind reanalysis from European Centre for Medium-Range Weather Forecasts (ECMWF). The research findings indicate that, rain exhibits an intensification effect on backscatter at low wind speeds, but this effect gradually diminishes with increasing wind speeds, eventually transitioning to an attenuation effect at a wind speed between 10-20 m·s −1 . At extremely high wind speeds above 20 m·s −1 , the rain initially increases and then decreases CSCAT normalized radar cross section (σ 0 ) as the rain rate increases. The sensitivity of CSCAT σ 0 to rain rate decreases as the incidence angle increases. Its sensitivity to wind speed decreases as the rain rate increases. The azimuthal modulation becomes more pronounced with higher wind speeds and smaller incidence angles. However, rain weakens the asymmetry and anisotropy. Furthermore, the HH polarization exhibits a more pronounced susceptibility to rain compared to the VV polarization.