signal attunuation problem. Conversely, the sensors should also be outside 

 the surf zone so that linear wave theory can be used with some confidence. It 

 was determined that the 8-m contour was the shallowest deployment site which 

 was also outside of the surf zone in typical storm conditions. Pressure 

 sensing elements are mounted approximately 1 m above the bottom and so are at 

 a nominal depth of 7 m. Attenuation of surface wave signals at this depth is 

 such that the signal-to-noise ratio of the pressure sensors permits observa- 

 tion of waves with frequencies up to 0.33 Hz. 



36. Figure A5 maps the relative locations of all 10 sensors. The full 

 array length is 255 m. The minimum sensor separation is 5 m. In light of the 

 lag- increment naming of the four-element array discussed above, the FRF array 

 can be called a 7-5-21-2-3-1-7-5 array. The 5-m minimum separation ensures 

 that aliasing will not occur for the highest frequency waves (those most 

 sensitive to aliasing). The wavelength of a 0.33-Hz wave in 8 m of water is 



sensor 10;* 



10 

 1 2 



34 



• 





• • 



• • 



o o 



mo 



sensor location (m) 



Figure A5 . Spacing and numbering of gages in the FRF linear array 



about 14 m. Since minimum gage separation is less than half this wavelength, 

 aliasing will not occur. 



37. It may be noticed that the sensor identification (ID) numbers are 

 not sequential. The reason for this is that the full array is actually broken 

 into subarrays , divided as follows : 



Subarray Name Sensors Used, ID# Length of Subarray. m 



Short Array 1,2,3,4,5 65 



Short- Intermediate Array 1,2,3,4,5,6 90 



Long- Intermediate Array 1,2,3,4,5,6,7 195 



Long Array 1,2,3,4,5,6,7,8,9 255 



A14 



