144 



From Eqns . 4.46, 4.47, and 4.48, one might expect that the 

 sum of the orthogonal slope energy spectra divided by the square of 

 the wavenumber would be equivalent to the water surface displacement 

 spectra for some frequency of frequencies, (Section IV. D. 9). 

 However, this would be true only for an idealized narrow wave spectra 

 with no frequency or directional leakage. 



8. Directional Estimates without the Absolute Pressure Gauge 



Estimates made of the wave direction without the absolute 

 pressure gauge are generally unreliable. Typical results calculated 

 using Equation 4.52 and the dP2 and dP3 signals for the data sets 

 illustrated in Appendix A are listed at the end of the appendix. 

 Equations 4.52 and 4.54 are valid if there exists only one wave 

 direction per frequency. When waves of one frequency arrive at 

 slightly different directions and spectral frequency bands are 

 contaminated by leakage, the validity of Equations 4.52 and 4.54 

 fails. As a general statement, it can be said that these equations 

 do not usually provide reliable estimates of the principal wave 

 direction in typical ocean wave analysis. The estimates might be 

 improved by some sort of data conditioning. 



