Ocean Surface Wave Measurement Using a Steerable High-Frequency Narrow-Beam Ground Wave Radar

Abstract

Ground wave radar is emerging as an important tool for routine monitoring of ocean surface conditions and for ship and sea-ice surveillance at ranges well beyond the line-of-sight horizon that limits conventional systems. A major Canadian advance in this field is the recent development of a long-range ground wave radar facility at Cape Race, Newfoundland. Owned and operated by the Northern Radar Systems Limited, this short-based radar system can monitor ocean surface conditions over a 120° sector out to a range of 200 km for sea state and to a range of 300 km for ocean surface currents. The near-real-time surface wave parameters are extracted from the Doppler spectra of the frequency-modulated interrupted continuous wave ground wave radar system. This paper presents a brief overview of the radar system and discusses the process of extracting the one-dimensional wave spectrum and significant wave height from the Doppler spectra. The latter involves both the direct inversion of the HF (high frequency) radar cross section of the ocean surface as well as the least square fitting of modeled UF spectra. The ground wave radar facility at Cape Race was used in the measurement of wave parameters during the SAR (synthetic aperture radar) wave spectra validation experiments, offshore Newfoundland during November 1991. The SAR is one of the sensors aboard the European Space Agency's Remote Sensing Satellite (ERS-1) launched in June 1991. The wave parameters deduced by the ground wave radar were evaluated against buoy measurements as well as against hindcast values from the operational wave model, Canadian Spectral Ocean Wave Model. The radar-deduced wave heights were also evaluated against wave height charts prepared routinely by the Meteorology and Oceanography Centre at Halifax, Nova Scotia. Overall, a very good agreement was obtained. The utility of the radar for nearshore wave analysis and nowcasting, as well as for offshore surveillance, is discussed.