137 



described in Equations ^-18 through A-24. If the first seven 

 directional Fourier coefficients, (i.e., N=3) , were developed, then 

 the directional spectra might be smoothed by a weighting function 



15 6 1.., ^. 



— cos -(6' - 6) (5_ii) 



such that Wo = 1, wi = 66/77, Wg = 15/28, and W3 = 5/21. 



6. Redundancy of dP2 and dPA Measurements 



If differential pressure gauges dP2 and dPA work correctly, 

 then the results of directional analysis of wave data using either of 

 these two collinear gauges should be nearly identical. To check 

 this, a number of wave records were analyzed using the signals from 

 the absolute pressure channel, dP3, and dP2, and then the signals 

 from the absolute, dP3, and dPA channels. Two of the results are 

 shown in Figures VI-12 and VI-13. Figure VI-12 illustrates the 

 energy spectrum and the non-smoothed directional spectra of the first 

 two peak energy bands for one data set using both combinations of 

 gauges. The energy spectrum, taken from the signals of the absolute 

 gauge, is the same for either gauge combination. There is good 

 directional agreement in this case of well-defined swell. Figure 

 VI-13 illustrates the energy spectrum and non-smoothed directional 

 spectra of the first two peak energy bands for another data set. The 



