78 



5.3 Computation Methods 



The LFI method for an array of water surface measurements can be broken down 

 into a similar sequence of steps as with the analysis of a pressure record: 



1. Pre-processing of record. 



(a) Determine estimate for level of noise in the record. 



(b) Determine estimate for magnitude and direction of Eulerian current. 



(c) Define a set of continuous records from each gauge from the discrete ob- 

 servations by cubic spline interpolation. 



(d) Specify spacing of output locations. 



(e) Compute mean zero crossing frequency. 



(f) Non-dimensionalize record and all parameters. 



2. Primary values of numerical solution parameters are chosen. 



(a) Window width (tq) 



(b) Order of solution (J) 



(c) Number of time samples of the water surface records within each window 



(M) 



3. Global solution is computed on an entire wave to provide first estimates for 

 local optimization 



4. For each selected output location, a window in the record is defined, and the 

 an LFI solution is computed. 



(a) Initial guess for the optimization is determined from the global solution. 



(b) Full nonlinear optimization for all unknown components of the potential 

 function is computed. 



(c) Results are checked for spurious solution. 



