An evaluation of least-squares and closed-form dual-angle methods for CODAR surface-current applications

Extraction of surface currents from first-order CODAR sea echo requires use of a model that allows signals from two bearings to contribute to the Doppler spectrum at a given frequency. This is called the dual-angle situation, and it applies over much of the coverage area. Two dual-angle techniques have appeared in the literature: a least-squares algorithm used with a crossed-loop antenna system, and a closed-form approach applied to a four-element square array. We evaluate these methods against realistic signal and noise scenarios encountered in CODAR operations, and study noustatistical biases remaining after infinite-ensemble averaging of the input voltage cross-spectral data. Based on these simulations, biases produced with the closed-form methods exceed those for the crossed-loop system analyzed with least squares by typically 150 percent.