Experimental Assessment of the Performance of High-Frequency CODAR and WERA Radars to Measure Ocean Currents in Partially Ice-Covered Waters

Abstract

igh-frequency radars (HFRs) measure ocean surface currents remotely through the Bragg scattering of radio waves by surface gravity waves with wavelengths shorter than 50 m. HFR range is affected by sea ice, which dampens surface gravity waves and limits wind fetch for adjacent open waters. HFR range sensitivity to sea ice concentration was empirically determined for two types of HFR?Coastal Ocean Dynamics Applications Radar (CODAR) and Wellen Radar (WERA)?installed on the shores of the lower St. Lawrence estuary, Canada, during winter 2013. One CODAR was operating at 13.5 MHz on the southern shore, and one WERA was operating at 16.15 MHz on the northern shore. Ranges were determined using a signal-to-noise ratio threshold of 6 dB for first-order Bragg scattering measured by the receive antenna elements. Ranges were normalized for expected ranges in ice-free conditions, using empirical relationships determined during summer 2013 between the range and surface gravity wave energy at the Bragg frequencies. Normalized ranges Γ decrease approximately linearly with increasing sea ice concentration C (averaged over the ice-free observational domain) with a slope close to ?1 for both HFR types, that is, Γ = 1 ? C. However, for a given sea ice concentration, range can vary significantly depending on the sea ice spatial distribution.