Comparison of Currents derived from X-band Radar and collected In-situ Data in Ameland Inlet

Abstract

Velocities derived from X-band radar were compared to depth averaged ADCP measurements in a complex tidal inlet system at Ameland, the Netherlands. Inclusion of depth assimilation and ensemble averaging in radar calculations led to smaller differences between ADCP and radar. The observed differences were clustered and related to water level elevations, wind velocities, wave periods, wave heights, spatial coherence in radar output and error metrics of the radar fitting procedure. Larger waves and higher wind velocities were observed to benefit radar agreement with ADCP results. Rising water levels benefitted agreement in east west direction. Falling water levels benefitted agreement in north south direction. Confidence intervals of the fitting procedure were observed to coincide with differences between ADCP and radar and potential for filtering based on them was shown. Nevertheless, an unclarified tendency towards northwestern bias, which may be specific to the comparison locations, remains. The radar at Ameland monitors the whole inlet system and provides current velocities everywhere in its range. This study shows that its currents are in good agreement with ADCP depth averaged currents throughout most of the tidal cycle. Furthermore, it stresses radar’s potential for better monitoring of the coast and for cost effective coastal field measurements to obtain large datasets, even in hydrodynamically very complex regions.