Implementing Quality Control of High-Frequency Radar Estimates and Application to Gulf Stream Surface Currents

Abstract

uality control procedures based on non-velocity parameters for use with a short range radar system are applied with slight modification to long range radar data collected offshore of North Carolina. The radar footprint covers shelf and slope environments and includes a segment of the Gulf Stream (GS). Standard processed and quality controlled (QCD) radar data are compared with 4 months of acoustic Doppler current profiler (ADCP) time series collected at 3 different sites within the radar footprint. Two of the ADCP records are from the shelf and the third is on the upper slope and is frequently within the GS. Linear regression and Bland-Altman diagrams are used to quantify the comparison. QCD data at all sites have reduced scatter and improved correlation with ADCP observations relative to standard processed data. Uncertainty is reduced by approximately 20% and linear regression slopes and correlation coefficients increase by about 0.1. At the upper slope site the QCD also produced a significant increase in the mean speed. Additionally, significant increase, averaging roughly 20%, in mean speed in the GS is apparent when comparing standard processed data and QCD data, concentrated at large range and at the azimuthal extremes of radial site coverage. Shifts in the distributions of the standard processed and QCD velocity estimates are consistent with removal of zero-mean noise from the observations, which has minimal impact where the radial site range is < 70 km and a large impact at greater range in the GS where mean currents exceed 1 m s-1.