129 



(c) Results are checked for spurious solution. 



i. If no solution, or a spurious solution, is found, the solution parameters 



are adjusted, and the optimization repeated, 

 ii. If a good solution is found, progress to the next window. 



6.3.1 Pre-Processing of Record 



The pre-processing of the measured records is essentially the same as presented in 

 the previous chapters. Estimates for the mean water level (h) and Eulerian current 

 {Ux and Uy) must be computed to define the propagation medium. Cubic splines of 

 the measured records are computed to provide continuous records for computation, 

 and the desired output locations are chosen. The records and all parameters and 

 variables are non-dimensionalized by the following parameters: the mass density of 

 water (p), acceleration of gravity (g), and the mean zero crossing frequency of the 

 measured records {uiz). 



6.3.2 Optimization Procedure 



The nonlinear optimization in the LFI method for the analysis of arrays of pressure 

 measurements is very similar to that used for the analysis of a single subsurface 

 pressure trace. In the single wave approach, the solution is somewhat easier. The 

 potential function used by the single wave approach is almost the same as that used 

 with a point measurement (both chapter 3 and Sobey (1992)), with the addition 

 of a directional component to the wave number. This results in a single additional 

 unknown, but the array of measurements provides at least three times as much data, 

 with gauges at at least three spatial locations to specify uniquely the directional 

 structure of the sea. The result is that the optimization tends to converge more 

 rapidly and robustly than with a single point measurement. 



When applying the method with the two wave potential function, there are far 

 more unknowns, and the optimization once again becomes somewhat tenuous. As 

 with the previous chapters, it is essential to identify a good initial estimate to reduce 



