along with the effect of buoy tilt on the heave. The magnetic declination is a 

 user input value that describes the compass deviation from true north at the global 

 position during, actual buoy measurements. 



ANALYSIS PROGRAM 



As mentioned earlier, the analysis scheme offered on these pages deals with 

 buoy transformations, corrections and declinations prior to the directional com- 

 putations, but following the calculation of auto and cross spectra. The software, 

 which uses a Fast Fourier Transformation (FFT) to calculate the auto and cross 

 spectra, was developed by Pierce at DTNSRDC. These details of the procedure will 

 not be presented here, but some of its characteristics include: (i) the data is 

 broken down into segments of a power of two, based on user input, (ii) a cosine 

 window is applied to each segment, and (iii) the segments are overlapped by 50 per- 

 cent. 



The flow chart of the directional wave program can be found in the Appendix. 



The program has two basic options. The first is to calculate the spectral density, 



the Fourier coefficients of the directional distribution, mean directions based on 



the first and second harmonic components, and rms spreading, among other useful 



information. The second option is to calculate the directional spreading of wave 



energy of each frequency. In this option, a choice of methods of spreading is 



offered between cos — ( - 9~) , a cosine Fourier series and the Longuet-Higgins 



2 

 method as mentioned earlier, three different weighting parameters are available to 



minimize or eliminate leakage in the Longuet-Higgins method. Further assumptions, 



corrections and errors will be discussed presently. 



COMPUTED RESULTS - A SAMPLE 



In accordance with the two basic options, two displays of the results are 

 outputted. The first display, as seen in Table 1, presents basic information, 

 spectral components, and directions. 



The Fourier components, A~ , A-^, B-^ , Ag , Bg - , the mean direction and prin- 

 cipal angle, i.e., first and second harmonics, respectively; and the root mean 

 square spreading about the mean direction are computed for each frequency. 

 Furthermore, the significant wave height, the spectral bandwidth parameter, the 

 broadness parameter, and the average period are derived from the spectrum. The 

 significant wave height, ( r^) ■} /o is defined as 



1U 



