Origin of storm footprints on the sea seen by SAR

This work provides (1) strong evidence that wave damping is due to rainfall; and (2) explains the origin of storm-induced footprints on the sea. The authors find some heretofore unobserved storm mechanisms. Explanations of storm induced patterns on the sea (called "footprints") first seen by SEASAT SAR in 1978 (Fu and Holt, 1982), have been unsupported by any corroborative data. Based upon previously unrecognized features of the SEASAT SAR echoes Atlas (1994) presented a more convincing explanation, but this too lacked independent data. The present paper deals with recent observations from the ERS-1 SAR (5.6 cm wavelength) which were made with simultaneous WSR-57 radar observations at Cape Hatteras. The key features of the footprints are: (1) an echo-free hole (EFH) where the sea radar cross-section (RCS) is greatly reduced; and (2) a region of increased RCS. In some cases, the EFH contains a bright spot of increased RCS. Both Fu and Holt (1982) and Atlas attributed the EFH to wave damping by rain. But backscatter experiments in the lab showed increases in RCS in the presence of rain, thus evidently contradicting the rain damping thesis. Atlas explains why these experiments do not necessarily preclude wave damping. DA shows that the turbulent eddy viscosity produced by heavy rain in salt water would rapidly damp short gravity waves. But this still does not prove that this occurs in nature