C-band radar signatures of rain over the ocean — Revisited

Envisat C-band SAR images acquired over the ocean have been screened for radar signatures of rain and compared with quasi-simultaneously acquired weather radar images, mostly provided by the Hong Kong Observatory. Compared to X- and L-band radar signatures of rain over the ocean, C-band radar signatures are much more complex because rain can increase or decrease the radar backscattering due to ring wave generation by the rain drops impinging onto the sea surface and due to wave damping by turbulence generated in the upper water layer by the impact of the rain drops. Which of these two mechanisms dominates, depends on rain rate, drop size distribution, wind speed, and the temporal evolution of the rain event. Stratiform rain usually causes an increase of the radar backscattering, while most of the other forms of rain cause a mixture of increased and decreased radar backscattering.