Dual HF radar measurements of sea waves from straight coastlines

Abstract

An important development in applied oceanography has been the development of surface wave HF radar systems, such as OSCR (Ocean Surface Current Radar), that can investigate coastal sea-surface processes from the shoreline continuously and in all weather conditions. OSCR is a 27 MHz pulse radar system normally used to measure surface currents from the shore out to ranges of about 45 km. However the system is increasingly being used to investigate waves out to about 25 km. In a typical deployment, two OSCRs are located 15-20 km apart along the coast so that their coverage sectors overlap over the sea area of interest. At the main site the radar is called the 'master' system and it controls the operation of the other 'slave' system via a radio link. Radar data is usually gathered on the master OSCR for a period of 5 minutes, followed by a similar period by the slave system. Each data set is processed by FFT analysis to give the Doppler backscatter power spectrum. It is these spectra that are used to infer ocean waves and currents. The OSCR transmitting antenna is a simple Yagi-Udah array that floodlights a 90/spl deg/ sector of sea. The receiving antenna is an 85 m long linear array of monopoles that is used to form beams with a width of about 7/spl deg/. These beams are generated electronically in specific directions so that the overlapped area of sea can be investigated on a 1 km grid scale. It is the performance of this receiving array subsystem that is the subject of this paper.