A new microwave technique for the measurement of ocean wave spectra has been compared with wave gauge output during extensive field testing at the Coastal Engineering Research Center's Field Research Facility, Duck, North Carolina. The method is based on the dual-frequency, or delta-k, technique for detecting long ocean waves by matching the modulation of short waves with the beat wavelength between two transmitted microwave frequencies. The new method, however, utilizes three microwave frequencies in order to reduce mean backscatter not related to short wave modulation. Prototype scatterometers have been built at L-band, and later, because of its suitability for aircraft use, at Ku-band. Wave spectra have been measured by both radar systems which, when properly normalized, agree well with simultaneous in situ measurements taken by conventional wave gauges at the pier site. Thirteen sets of spectra have been computed, five of which correspond to a situation in which a local wind sea was generated and then decayed. Although the present experiment does not demonstrate the directionality of this new technique, its similarity to previous delta-k measurements, which do demonstrate directionality, leads us to conclude that this new method is a promising technique for measuring the directional ocean wave variance spectrum.
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