Comment on ‘Single station ocean current vector measurement: Application of the spaced antenna (SA) technique’

Abstract

A “spaced antenna” (SA) technique for HF ocean‐surface current measurement was introduced by May et al. [1989]. It was stated that the SA technique can measure transverse surface current speed from a single HF radar station, in addition to the radial speed that is conventionally obtained; it is claimed, therefore, that a single station can thereby measure the total current vector, eliminating the need for two radars. This sequel presents the derivation showing that the SA technique actually measures the radial speed's angular variation with respect to bearing, rather than the transverse current speed. The former is equal to the transverse speed only when there is no curvature in the current streamlines. Using reported voracities, we show that neglect of the resulting curvature in attempting to deduce the transverse speed produces errors too large to allow accurate single‐site current mapping based on SA measurements for normal coastal operation. We consider applications where the SA should prove advantageous, and give limits on radial variation for required transverse speed accuracy.