Capability of Radarsat-1 for estimation of ocean surface current on the Scotian Shelf

Doppler shifts in space-based synthetic aperture radar (SAR) data are due to movement of objects in the image area. These frequency shifts are most obvious in fast moving point targets such as ships. However, an area target such as the sea surface can also cause a measurable Doppler shift from which ocean surface currents can be estimated. We compare surface currents derived from three standard mode Radarsat-1 scenes over the Scotian Shelf to in situ currents measured with 21 self-locating datum marker buoys (SLDMBs). The SLDMBs drift with the local surface current, and their locations, obtained every 30 minutes via Argos satellite, are used to calculate the current. Three Radarsat-1 scenes were processed by Atlantis Scientific of Ottawa, Canada, to obtain the component of the surface current vector perpendicular to the path of the satellite. The results show that the noise in the derived Doppler shift was comparable to the Doppler shift expected from the relatively low surface currents prevalent on the Scotian Shelf. While it was concluded that present space-based SAR technology cannot provide accurate surface current data for Scotian Shelf conditions, the methodology and results provide a useful metric by which future SAR systems can be evaluated.