Impacts of Oil Spills on Altimeter Waveforms and Radar Backscatter Cross Section

Ocean surface films can damp short capillary-gravity waves, reduce the surface mean square slope, and induce ‘‘sigma0 blooms’’ in satellite altimeter data. No study has ascertained the effect of such film on altimeter measurements due to lack of film data. The availability of Environmental Response Management Application (ERMA) oil cover, daily oil spill extent, and thickness data acquired during the Deepwater Horizon (DWH) oil spill accident provides a unique opportunity to evaluate the impact of surface film on altimeter data. In this study, the Jason-1/2 passes nearest to the DWH platform are analyzed to understand the waveform distortion caused by the spill as well as the variation of r0 as a function of oil thickness, wind speed, and radar band. Jason-1/2 Ku-band r0 increased by 10 dB at low wind speed (<3 m s) in the oil-covered area. The mean r0 in Ku and C bands increased by 1.0–3.5 dB for thick oil and 0.9–2.9 dB for thin oil while the waveforms are strongly distorted. As the wind increases up to 6 m s, the mean r0 bloom and waveform distortion in both Ku and C bands weakened for both thick and thin oil. When wind exceeds 6 m s, only does the r0 in Ku band slightly increase by 0.2–0.5 dB for thick oil. The study shows that high-resolution altimeter data can certainly help better evaluate the thickness of oil spill, particularly at low wind speeds.