New signal processing techniques for phased-array oceanographic radars: self-calibration, antenna grouping, and denoising

Original techniques are proposed for the improvement of surface current mapping with phased-array oceanographic High-Frequency Radars. The first idea, which works only in bistatic configuration, is to take advantage of a remote transmitter to perform an automatic correction of the receiving antennas based on the signal received in the direct path, an adjustment that is designated as “self-calibration”. The second idea, which applies to both mono- and bistatic systems, consists in applying a Direction Finding (DF) technique (instead of traditional Beam Forming) not only to the full antenna array but also to subarrays made of a smaller number of sequential antennas, a method which is referred to as “antenna grouping”. In doing this, the number of sources can also be varied, leading to an increased number of DF maps that can be averaged, an operation which is designated as “source stacking”. The combination of self-calibration, antenna grouping, and source stacking makes it possible to obtain high-resolution maps with increased coverage and is found robust to damaged antennas. The third improvement concerns the mitigation of noise in the antenna signal. These methods are illustrated with the multistatic High-Frequency Radar network in Toulon and their performances are assessed with drifters. The improved DF technique is found to significantly increase the accuracy of radar-based surface current when compared to the conventional Beam Forming technique.