Interpretation of VHF radar echoes from a Complex Flow Field

Bragg lines on spectra from ocean radar systems are broadened when echoes come into the antenna from different azimuths. Phased-array systems minimise the effects of this by selecting a small target area on the sea surface by beam-forming and range-gating. While phased array systems are better conditioned for high spatial resolution than direction finding systems, in some cases there may be fine structure in the surface current field within the smallest of target areas. In estuaries or other areas where there are sand banks and low islands there is potential for contamination from side-lobes of phased array antennas to contaminate adjacent pixels. This paper uses data from an area of highly complex flow field in Dingle Bay, Ireland to examine the complex structure of Bragg echoes. A numerical hydrodynamic model is used as an aid in understanding the degree of structure to be expected in the Bragg lines, and an improved analysis is described to extract surface current data from the radar echoes.