- 3 



Several types of underwater in- si tu systems have been 

 suggested; some of which are operational presently. Such 

 instruments include tri-axial current meters (van Heteren and 

 Keyser , 1981) , bi-axial current meters with one pressure transducer or 

 wave staff (Aubrey, 1981 ; Nagata,196^; Bowden and White, 1966; 

 Simpson, 1969) , arrays of pressure transducers (Peacock, 197^; 

 Seymour, 1978; Mobarek, 1965 ; Chakrabarti , 1971 ; Chakrabarti and 

 Snider, 1973; Panicker and Borgman, 1970; Ploeg,1972), and 

 measurement of the bi-axial components of the force on a sphere 

 together with bottom pressure fluctuations (Suzuki , 1969) . A review 

 of many procedures that have been used to make directional wave 

 measurements is presented by N, N, Panicker (1974), K. Rikiishi 

 (1977), and more recently within the Proceedings of the National 

 Reasearch Council Workshop on Wave Measurement Technology (1982) . 



Data from some current meter systems is often suspect after 

 deployment because of the suseptibi 1 ity of the instrumentation to 

 bias from bio-fouling and corrosion. Bottom-mounted pressure 

 transducers, on the other hand, have been used with considerable 

 success for wave sensing for several years (Forristall , 1981) • 



The concept of measuring the directional characteristics of 

 waves is fairly straightforward. If one considers a long wave crest 

 approaching parallel to the alignment of two pressure sensors, as in 

 Figure I-l, it is easy to imagine both sfensors recording the crest 

 passage simultaneously. If the wave crest approaches obliquely to 



