Thesis topic: Ocean surface observations from SAR combining Doppler signal and NRCS
Advisors: Alexis Mouche and Bertrand Chapron
To investigate in what degree the Doppler range velocity retrieved from SAR imagery relates to the corresponding SST patterns qualitatively and quantitatively and how large current speed is associated with strong SST gradient. The sensitivity of Doppler shift and Normalized Radar Cross Section (NRCS) to different scales of ocean surface waves will be investigated and their relative behaviors over SST fronts or atmospheric fronts. All these studies are to support retrieving ocean surface wind and current vectors using NRCS and Doppler information.
The surface current velocity maps over Agulhas Current retrieved from SAR imagery are available since mid 2007 and the synchronous SST imagery acquired by Seviri can be adopted to examine if there is any empirical function between these two variables. Preliminary statistics is required to determine a qualitative relationship indeed exists and further neural network is expected to quantify this function.
The wave spectra are derived to indicate the various scales of surface waves, then the Doppler shift and NRCS are exploited to research their sensitivity to different surface waves. The imaging model is expected to quantify the individual sensitivity of Doppler shift or NRCS to wave scales. Then the observation results can be compared with the model outputs and in return to improve the imaging model.
Effects of wind and SST perturbations on the surface roughness can be researched by combining satellite observations and model results. I plan to exploit long-term wind product from scatterometer and SST data over Agulhas Current to investigate their quantitative relationship. Then the applicability of this function to SAR condition can be tested using NRCS, range velocity map and synchronous SST imagery. This study may further deepen our understanding of SAR imaging principle.