Investigation of Coherent and Incoherent Scattering from Lakes Using Cygnss Observations

Spaceborne GNSS reflectometry has shown ability to observe the global inland water distribution. It allows generating dynamic maps of rivers, wetlands and inundations using the large variation in the received power while the ground track crosses those objects. Here, we analyze the change of the reflected signal's power and coherence due to surface roughness and cover (ice) observed in the CYGNSS delay-Doppler maps for Qinghai Lake, China. It is shown that a significant attenuation of the reflected coherent signal and emergence of the diffuse component occurs due to wind-generated surface waves. The comparable attenuation effect of the coherent component is observed in the case of the frozen lake. It takes place due to the lower value of the average Fresnel reflection coefficient of ice. A similar effect may occur for reflections from wetlands, when open water and water covered by vegetation could produce comparable reflected powers, however, due to different mechanisms. Understanding the relative scattering characteristics of wetlands in contrast with rougher bodies such as lakes is important for the development of algorithms to detect their dynamic changes.