- 57 



The wavenumber, k, and the pressure response function are 

 generated for the frequencies 



*^^''^- ^ uKt ^"""-^^ '■ "^ " 2,3, ...N/2 (4.39) 



where N is the number of sample points analyzed and At is the 

 sampling interval. The water depths used in the calculations include 

 the tidal variation computed earlier. 



8. FFT and Conversion to Water Surface Terms 



The absolute record, the four differential records, and the 

 two curvature records are processed by the Fast Fourier Transform 

 (FFT) and the resulting Fourier coefficients divided by the pressure 

 response function and specific weight of the seawater. Frequency 

 bands greater than 2 rad/sec (wave periods less than 3.14 seconds) 

 are disregarded because of the error inherent in dividing these high 

 frequency bands by their respectively small K values. 



The absolute record is then comparable to: 



n(.x,y,t) = - cos (k^x + k^y - at) (in.) (4.40) 



and the differential records to: 



