20 



With z defined to be zero at the mean water level (77) and Eq. 2.7 as the potential 

 function, B becomes (Sobey 1992): 



B = lj,. + iVf-iMi^)' (2.15) 



and all the terms in Eq. 2.10 are defined by the potential function, allowing the 

 dynamic pressure to be computed from the kinematics. 



2.2 Finding the Solution 



The bulk of the LFI method is the process of determining appropriate values for 

 each of the parameters, uj, k, kx, and Aj, in the potential function (Eq. 2.7) for each 

 window in time. The result is a set of potential functions that completely describe the 

 kinematics of the wave field in the region of the measurement, each separate window 

 in time being described by a unique and independent potential function. 



In the case of subsurface measurements, the location of the water surface is also 

 required. Determination of the parameters of the potential function, as well as the 

 location of the water surface, is accomplished through nonlinear optimization that 

 matches the measured record and minimizes the error in both free surface boundary 

 conditions. Sobey (1992) applied the LFI method to the interpretation of a single 

 water surface trace. The following chapter applies the method to a subsurface pressure 

 record. 



