A Comprehensive Study on Current-Wave-Radar Backscatter Interactions in a River Mouth and Their Effect on Along-Track InSAR Data

As demonstrated on many occasions, airborne and spaceborne along-track interferometric synthetic aperture radars (along-track InSARs) can provide direct measurements of line-of-sight velocity fields at high spatial resolution. To derive ocean surface current fields from InSAR data, one has to convert the measured velocities into horizontal velocities and apply corrections for contributions of wave motions. This is a challenging task because the wave contributions can be of similar magnitude as the currents of interest and exhibit significant spatial variations due to current-wave interaction. Traditionally, we have computed the corrections using a numerical SAR/InSAR imaging model, but this approach has a number of limitations. In this work, we try to develop a new current retrieval technique, which is expected to be more reliable than the traditional one and applicable to a broader variety of scenarios, including cases with strong wave shoaling and breaking. A comprehensive data set from an experiment at the mouth of the Columbia River on the U.S. West Coast, consisting of several along-track InSAR images from the satellite TerraSAR-X, corresponding current fields and wave spectra from the numerical model Delft3D/SWAN, and data from a variety of in-situ sensors, enables us to study in detail how differences between InSAR velocities and surface currents are related to wave properties and to what extent these relations are consistent with our SAR/InSAR imaging model. Furthermore, we can extract wave and wind information from visible signatures in the SAR intensity images. The combined analysis of the identified velocity differences and measured, modeled, and SAR-derived wave properties enables us to develop a semi-empirical model for estimating InSAR velocity corrections based on information derived from the InSAR data set itself. We present some key results of our analyses and first examples of corrected surface current fields obtained using the new technique.