135 



crossings in the record. The additional data provided by the array of measurements 

 provides for a more robust optimization than with a single subsurface pressure mea- 

 surement. As well as providing additional data, the spatial array provides information 

 about the evolution of the wave field in space, helping to define the local wave number 

 more clearly. This is in contrast to the analysis of a point measurement, where the 

 spatial evolution of the wave field must be determined entirely from the measured 

 temporal evolution, coupled with the governing equations. As a result, adjusting the 

 solution parameters is necessary less often than with a single measurement. 



6.4 Theoretical Records 

 6.4.1 Single Wave Records 



The following results are from "measured" data generated by Fourier steady wave 

 theory (Sobey 1989), providing a near-exact solution for steady waves that provides 

 the complete kinematics. The data used are a simulation of data that might be col- 

 lected by a DWG-1 pressure array (Howell 1992). The DWG-1 is a reliable, easy to 

 deploy pressure array. The unit is capable of including up to six independent pressure 

 transducers, but is frequently used with three transducers, arranged in an 1.6 m equi- 

 lateral triangle (fig. 6.1). Three measurements were chosen for the theoretical data, as 

 three is the minimum number required to provide directional information. Additional 

 measTirements would provide overspecification, and can easily be accommodated in 

 the formulation. 



Shallow Water Figure 6.2 is a steady shallow wave generated by 18th order Fourier 

 theory with the following parameters: wave height = 3m, period = 10s, water depth 

 = 5m, direction of travel 10 degrees from the x-axis, and an opposing Eulerian current 

 of 2m/s. This is a near limit wave in this depth water, with this opposing current. 

 The pressure array is located at the bottom. The parameters of the LFI solution are: 

 window width = Is (tq = O.IT^), fifth order (J = 5), with 6 samples on the water 

 surface, and 6 samples on each of the pressure records [M — I = 6), resulting in 30 



