LARGE-SCALE MAPPING OF OCEAN SURFACE CURRENTS WITH DUAL OVER-THE-HORIZON RADARS

DETAILED information about near-surface ocean currents is needed for e ffective fisheries management, pollution mitigation, search and rescue , and climate studies, but the present generation of measurement techn iques provides only limited spatial and temporal resolution or coverag e(1,2). In near-coastal environments, pairs of shore-based high-freque ncy radars have been used to map surface currents over an area of a fe w hundred square kilometres(3,4). The potential for mapping open-ocean current fields has been demonstrated using military high-frequency ra dars that can be used to 'see' over the horizon for thousands of kilom etres by reflecting signals off the ionosphere. But using one radar, o nly one current component can be mapped by this method(5). Here we rep ort the mapping of surface-current vectors obtained from simultaneousl y employing two such radar systems with overlapping coverage. We obtai n a current map in the Florida Straits, about 1,500 km from the radars , covering two 70,000 km(2) areas at a resolution of 10 km and 0.1 m s (-1). As it employs only about 2% of the radars' potential coverage, t he test shows the potential of this technique for mapping the more ene rgetic features of ocean circulation-such as boundary currents and mes oscale eddy systems-over vast ocean areas.