Backscatter and Doppler Velocities from Ocean Surface Currents and Sea Ice in Synthetic Aperture Radar

A Synthetic Aperture Radar (SAR) emits and records long wave electromagnetic signals, using a side looking configuration and the motion relative to the Earth surface to obtain high resolution images. It has recently been demonstrated by Chapron et al. (20 03, 2005) and Johannessen et al. (2008) that anomalies in the radar beam centre Doppler signal - the Doppler centroid - is a measure of the line of sight velocity of the moving ocean surface. This complements the backscatter measurements and offer better quantitative interpretation of the surface roughness pattern and upper ocean conditions, and it is applicable to the measurement of sea ice motion. The goal of this project is, firstly, to retrieve ocean surface velocity from SAR backscatter and Doppler c entroid anomalies by removing effects from wind and waves. This is not trivial and requires auxiliary information about the surface conditions (Chapron et al., 2003, 2005), and the use of models to estimate the different contributions. Secondly, using the Doppler centroid anomaly to estimate sea ice drift will be investigated. With the Doppler centroid information available from SAR since mid 2007, we further intend to create climatological high resolution maps related to both sea ice drift and ocean surf ace velocity. Validation will be performed over selected areas with access to altimeter data in combination with the improved geoid obtained with the GOCE Earth Explorer mission, coastal HF-radar, hydrodynamic ocean model and surface drifter data. Validat ion of ice data will be performed by comparison to ice drift estimated from pattern recognition in SAR backscatter. The project will contribute towards the development of an inverse method for estimation of surface current by the use of SAR backscatter a nd Doppler signals, and the development of algorithms, and calibration and validation routines for the Sentinel-1 SAR.