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Choice of Order 



The choice of order for the analysis of arrays of pressure measurements is essen- 

 tially the same as for a single pressure measurement. See chapter 3 for a detailed 

 discussion. In general, lower orders are necessary for deep water than shallow water, 

 with higher than third order unlikely to be necessary in deep water. Shallow water 

 may require up to fifth or sixth order in order to capture near limit waves. 



Choice of Window Width 



The choice of window width is also very similar for the analysis of pressure arrays 

 as it is for the analysis of a single pressure measurement, or arrays of water surface 

 measurements. Window widths of a minimum of about 1/10 the zero crossing period 

 are required, with the occasional need to widen the windows near zero crossings. The 

 additional data provided by the array of pressure measurements allowed a solution to 

 a very steep shallow water wave at high order with a window width of O.lTz, where 

 a similar solution required the window width to be doubled to 0.2T^ when there was 

 only a single point pressure measurement available (Section 3.4). 



Number of Nodes on the Water Surface and Pressure Records 



The criteria developed in the previous chapters for the number of water surface 

 nodes are applicable here. J+ 1 points are required to specify uniquely a Fourier series 

 of order J. In order to keep the order of the water surface consistent with the order 

 of the potential function, at least M = J + 1 water surface nodes should be used. The 

 same number of points on the measured pressure records is usually adequate. For the 

 standing and short-crested waves, additional equations were needed to specify the 

 solution, so / = J -|- 3 points on the pressure records were used. The results are not 

 highly sensitive to this parameter, provided sufficient samples are used to define the 

 local curvature and specify the system of equations. More points on the measured 

 pressure records will assist in accommodating noise in the record. 



