An investigation of double-peaked HF radar spectra via a convolution/de-convolution algorithm

The width of the Bragg lines (peaks) in the Doppler frequency spectrum for high frequency (HF) radar systems operating in an ocean environment are principally determined from the length of the time series from which they are produced. Theoretically, the peaks are single and narrow when the surface current field is uniform within the spatial scale of the radar target cell. On some occasions, however, these Bragg regions of the spectrum are broadened or even double-peaked. This phenomenon imposes a problem for surface current mapping since it is the frequency of the Bragg line which is used to determine the radial component of the current associated with a particular target cell. Here an algorithm is developed to first simulate the occurrence of ´split´ Bragg peaks observed when a simple current shear exists within a single cell observed by a HF radar whose receive (RX) antenna system consists of a linear, phased array. While it is not critical to the outcome of the model, it is assumed that the incident radiation is a simple pulsed sinusoid. The algorithm, which essentially consists of the convolution of the RX beam with the target cell current regime, reveals the nature of the changing Bragg structure as the beam is scanned through the region of interest over the ocean surface. Finally, the idea of extending the concept is broached to extend the algorithm to deconvolve the simulated Doppler results to reveal the bimodal current distribution.