Current Shear Mapping in the Open Ocean

Our line of HF radars can be used to map ocean currents and vertical current shear at kilometer resolution. From the latter measure, under certain conditions it is possible to derive the vector wind field based on stress continuity assumptions across the air-sea interface as described in presentations listed elsewhere. We have completed an ONR SBIR project to design a multi-frequency HF radar to derive such vector wind fields from shear measurements, which led to several components of our multi-frequency capability.

An example of radial components using 30 radar frequencies to probe depths between tens of centimeters and three meters are shown in the figure below. These resulted from a Navy experiment conducted off San Diego California SPAWAR Naval experimental facility. Each symbol represents a measurement made at a single radar frequency from a set of 3 data collections covering a 45-minute period. A prototype of our ISR_DOA_M radar, with 4 receive elements, was used to collect these data. Proprietary Direction-of-Arrival algorithms were used to determine the radial velocity and direction for each plot shown. When six different directions are plotted (individual colors shown), the outline of an eddy structure can be seen at depths below one meter. In the top, layers, the effects of wind driven near-surface shear in the top 50 cm can be seen as a logarithmic dependence, as seen from different directions to the wind. Between these two regions, mixing must occur that masks the sub-surface eddy structure.

ISR Sensing: Current Shear Mapping in the Open Ocean

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