80 



of the approach, this is the local mean water level, rather than a global still water 

 level, which might be different, and would be less appropriate. As with subsurface 

 measurements, the precision of this value is not critical, as h is only used to locate 

 the origin of the coordinate system for the potential function. 



The Eulerian Current 



The Eulerian current, Ux and Uy^ completes the description of the propagation 

 medium of the waves, and an accurate estimate of its magnitude and direction is 

 important. The measured water surface traces provide no information about the 

 current field, so the information needs to be provided from other sources. See Section 

 3.3.1 for a detailed discussion of this important parameter. 



Spline of the Records 



As with the previous chapter, a set of continuous records is computed by cubic 

 spline interpolation among the measured points at each gauge, allowing complete 

 flexibility in the choice of window widths and location of samples in time of the 

 records. 



Output Locations 



The spacing of the desired output locations must be chosen to determine the 

 placement of the windows. Each window is computed independently so there is no 

 restriction on the spacing of the output windows. In addition to selecting the output 

 spacing in time, in can be useful when using an array of instruments to determine a 

 single central location within the array at which to define the solution. 



Non-dimensionalization 



In order to prevent spurious solutions due to the comparisons of errors of different 

 dimensional quantities, all parameters and variables are non-dimensionalized before 

 computation with scales defined by the same physically identifiable parameters used 



