ADVANCED DIRECTIONAL SEA SPECTRUM STUDIES WITH BRIBIE ISLAND MF LOWERHF SURFACE-WAVE RADAR

The directional factor of sea spectra is an important oceanographic qu antity which has been measured infrequently by a limited number of tec hniques. Here I report the use of a large-phased antenna array transmi tting at 1.98, 3.84, and 5.80 MHz for measuring the directional factor from the observed first-order surface-wave sea echoes (ie., those due to Bragg resonance) measured simultaneously at many azimuths through rapid, digital control of beam direction. This measurement process com pares with the extraction of directional factors from second-order rad ar cross sections in that both techniques rely on the statistical qual ity of observations and the stability of integral inversion algorithms employed. Preliminary observations show that, in principle, this new technique can be used to measure the directional factor automatically, including dominant sea direction and angular spread with high resolut ion (+/- 2-degrees) in near-real time. The strategy required to achiev e high accuracy is outlined.