12 



the instrument's dynamic range and reaches its greatest response 

 level for waves between four and six second periods. Sensitivity to 

 longer period waves increases with increasing water depth. 

 Differential pressure response increases as the transducers are 

 raised off the seafloor, as expected, and the greatest sensitivity 

 shifts to waves of higher frequency (Figure II-4) . 



In Figures II-l through II-A, the response of the 

 differential transducer was developed over a pressure sample spacing 

 of only three feet — less than one-sixth of the gage length of 

 conventional pressure sensor array systems. Typical arrays generally 

 develop two orthogonal measurements of water surface slope by 

 sampling points separated by twenty to thirty feet. The differential 

 pressure gauge concept, then, suggests that more efficiently measured 

 directional information can be obtained with a considerably smaller 

 instrument than is presently used. 



B. The Differential Pressure Gauge Directional Wave Monitor 



To test the effectiveness of an array using differential 

 pressure transducers, the differential pressure gauge directional 

 wave monitor (DPG) was developed. Using small distances between 

 differential pressure sampling points, it was possible to design a 

 system which directly measures the water surface slope yet is 

 physically smaller, more manageable, and potentially more accurate 



