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are required to record. Hence, the pressure difference across an 

 array is calculated by subtracting two large numbers in order to 

 generate a very small number. Such a system lends itself to inherent 

 inaccuracies. For example, a bottom-mounted transducer in twenty 

 feet of water records the passage of a three foot wave crest of nine 

 second period with a value of 24.78 psia compared to the 23.64 psia 

 reading under still water. A similar transducer placed twenty feet 

 away at a 45 degree angle to the wave crest would report 24.69 psia 

 at the moment the crest passes its neighboring gauge. (Linear wave 

 theory is utilized for this example.) The arithmetic difference 

 calculated between the transducers, 0.09 psia, is less than one half 

 of one per-cent of the still water value each transducer would record 

 or less than nine percent of the dynamic pressure caused by the 

 passing wave. The difference can be improved by increasing the 

 distance between transducers — at the expense of a more physically 

 unmanageable array, greater error in the assumption of linear water 

 surface slope, and introduction of directional ambiguities for the 

 higher frequencies present. 



It is the contention of this thesis that the accuracy of the 

 directional wave spectrum calculated from such small differences 

 between large pressure values is questionable. The accuracy and 

 physical size of the pressure sensor array can be improved by 

 utilizing differential pressure transducers designed to record small 

 pressure differences between two points. This thesis will document 



