Comparisons between HF radar and SAR current measurements in the Iroise Sea

In coastal oceanography, currents are difficult to measure with a good temporal and spatial resolution. Nevertheless, precise knowledge of these currents is crucial for certain applications such as pollution monitoring. Up until now, very few instruments have been able to provide current measurements. Although techniques based on HF radar and satellite-based Synthetic Aperture Radar(SAR) are promising, comparisons between these two approaches must be carefully formulated since the approaches differ in terms of scattering geometry, radiation frequency, and antenna footprint. In this document, we present a brief review of these two approaches as well as a comparison between them using data acquired over the Iroise Sea in France. Since the dominant source of currents in this area is tidal in nature, we also compare the results to the currents predicted by the tidal model MARS2D. The results are encouraging: the SAR-derived currents (specifically, the component of the current in the radial direction along the SAR beam) are qualitatively similar to the equivalent projected radial components deduced from HF measurements and MARS2D output. It must be noted, however, that the HF radar results may be compromised by the presence of island, and the SAR results may be compromised owing to the sensitivity to wind waves.