“wavesonar” - an Upward-looking Sonar for Wave Measurements on the Continental Shelf

An upward-looking sonar instrument, the Ice Profiling Sonar (IPS), has been developed, and successfully used for obtaining time series measurements of ice keel depths over the continental shelves of the Arctic in support of scientific research. The IPS instrument capabilities have since been expanded to provide accurate measurement of ocean waves. This new instrument, the WaveSonar, uses a high frequency acoustic transducer (420 kHz), with a very narrow conical beam (2o width at -3 dB) to minimize the spatial smoothing of surface waves across the sonar footprint. With low power consumption, and large storage capacity (64 Mbytes flash EPROM), the instrument is capable of continuous measurements of wave amplitude at a sampling rate of 1 Hz over deployments of up to nine months. From March 4 to April 28 1998 an evaluation of the performance of this instrument, through intercomparison with a Waverider buoy, was conducted in open ocean conditions off the Pacific west coast. Instantaneous wave heights of up to 11.5 m were measured. The results show good agreement between the WaveSonar and Waverider measurements. The WaveSonar has the advantage of operating from the relative safety of the ocean floor, thereby avoiding surface hazards such as ships, vandalism and adverse weather.