HF radar wave measurements in the presence of ship echoes - problems and solutions

HF radar is an important tool to remotely measure oceanographic parameters like currents and waves from shore over large areas up to 6500 km/sup 2/. Maps of these parameters can be obtained 3 times per hour. In areas of high ship traffic, there are ship echoes within the radar backscatter signal, which can appear in the frequency bands of the Doppler spectrum which are used to extract current- and wave information. While the current speed is derived from the first-order Bragg peaks, wave height and direction is calculated from the second-order bands around the first-order peaks. The second-order bands require 15 to 20 times the bandwidth of the first-order peaks and their amplitude is about 20 dB lower. Due to these facts, ship echoes can cause problems especially to wave algorithms. This paper discusses the special signatures of ship echoes and shows possibilities to identify and to track ships.