Abstract's details
A new look at the Ku-C backscatter relationship to analyze sigmabloom
CoAuthors
Event: 2017 Ocean Surface Topography Science Team Meeting
Session: Others (poster only)
Presentation type: Type Poster
Contribution: not provided
Abstract:
Most altimeters operates at dual frequencies, in general Ku (13.5GHz) and C (5.3GHz) band. The relationship between the two band backscatter has been used to detect the altimeter samples affected by rain samples using the differential attenuation of the signals by liquid water. However, the KU-C band relationship contains much more informations than the rain attenuation. In particular it could provide a new way to analyze and interpret the altimeter sigmabloom events. The analysis of Jason1 and 2 and Envisat data during the Deepwater Horizon oil spill and the comparison with oil spill thickness and extent data showed that the presence of oil spills on the sea surface can distort the altimeter waveforms and cause 'blooms' in the radar backscatter cross-section signal, but compresses the surface capillary wave and reduce the sigma0 in synthetic aperture radar (SAR) imagery.
The comparison of high resolution surface sigma0 obtained by waveform inversion method and ERMA oil cover fields showed that locally the Jason-1/2 Ku band sigma0 increased up to 10 dB in low wind speed. At low wind speed (<3 m.s^{-1}), the mean sigma0 in Ku and C bands increased by 1.0 to 3.5 dB for thick oil and 0.9 to 2.9 dB for thin oil while the waveforms are strongly distorted. At medium winds (up to 6 m.s^{-1}) the mean sigma0 bloom and waveform distortion in both Ku and C bands weakened for both thick and thin oil. For larger winds (> 6 m.s^{-1}) only does the Ku band sigma0 slightly increase by 0.2-0.5 dB for thick oil. (See Y. Cheng et al Poster)
A further analysis reveals that surface films have a differential impact at Ku and C band depending on the existing surface roughness (due to wind) and film thickness. This differential impact reflects in the Ku-C band relationship by modifying the departure from the "normal" Ku-C band relation. Examples of the modification of the Ku-C band backscatter difference by surface film of different thickness will be analyzed and compared to low winds cases to show that the departure from a "normal" Ku-C band relation can be used to detect the presence of surface film.
The Jason2 archive has thus been processed to analyze the sigmabloom events. In a first step, all the bloom events (whatever their length) of sigma0 larger than 16dB are detected and their characteristics (occurrence, geographical distribution, length, strength, wind speed) analyzed. In a second step, the departure from the Ku-C band relationship within the bloom is analyzed to give a tentative estimate of the presence of surface films.
The comparison of high resolution surface sigma0 obtained by waveform inversion method and ERMA oil cover fields showed that locally the Jason-1/2 Ku band sigma0 increased up to 10 dB in low wind speed. At low wind speed (<3 m.s^{-1}), the mean sigma0 in Ku and C bands increased by 1.0 to 3.5 dB for thick oil and 0.9 to 2.9 dB for thin oil while the waveforms are strongly distorted. At medium winds (up to 6 m.s^{-1}) the mean sigma0 bloom and waveform distortion in both Ku and C bands weakened for both thick and thin oil. For larger winds (> 6 m.s^{-1}) only does the Ku band sigma0 slightly increase by 0.2-0.5 dB for thick oil. (See Y. Cheng et al Poster)
A further analysis reveals that surface films have a differential impact at Ku and C band depending on the existing surface roughness (due to wind) and film thickness. This differential impact reflects in the Ku-C band relationship by modifying the departure from the "normal" Ku-C band relation. Examples of the modification of the Ku-C band backscatter difference by surface film of different thickness will be analyzed and compared to low winds cases to show that the departure from a "normal" Ku-C band relation can be used to detect the presence of surface film.
The Jason2 archive has thus been processed to analyze the sigmabloom events. In a first step, all the bloom events (whatever their length) of sigma0 larger than 16dB are detected and their characteristics (occurrence, geographical distribution, length, strength, wind speed) analyzed. In a second step, the departure from the Ku-C band relationship within the bloom is analyzed to give a tentative estimate of the presence of surface films.