Mapping ocean currents using over-the-horizon HF radar

Abstract

A high spatial resolution HF radar operating in the skywave mode has been used to map a warm water eddy and the Gulf Stream in the North Atlantic ocean by means of remotely sensing the current structure of the eddy. A bistatic system was used, transmission being provided by the NRL MADRE radar, in Chesapeake Beach, Maryland, while reception of the backscattered signal was carried out with the ONR 1100m array at Whitehouse, Virginia, some 80 miles south of the transmission site. Currents were measured by determining the shifts of the Bragg lines of the scattered signal due to the translation of the water mass in a given radar scattering cell, which measured typically 6 km in range and 12 km in azimuth. The eddy was located approximately 1200 km from the east coast; two-way E-layer propagation was used for radar coverage to this range. Path quality was sufficiently stable to allow radial velocity resolution of the order of 12cm/s, using coherent integration times of 100 s. This technique offers a capability not available with infrared setallite sensors, which measure thermal features that can be masked by several causes.