2. Determination of Wave Direction from an Array of Sensors . 



Information on wave direction is available from analyses of the rec- 

 ords obtained from an array of wave sensors. In essence, this procedure 

 is based on an assumption about the geometry of the water surface and the 

 relation between the wave height and the pressure, the velocity or both, 

 as a function of depth. The assumption may have a deterministic or prob- 

 abilistic form, but it must be expressed in analytic form so that coeffi- 

 cients obtained from the wave record analyses can be used to specify the 

 distribution of wave directions. 



The simplest model assumes that the important waves are low, mono- 

 chromatic, unidirectional, long crested, and are traveling without change 

 of shape over a horizontal bottom. If these conditions hold and the phase 

 differences between three wave gages in a two-dimensional array can be 

 measured, a unique wave direction can be derived from the data. A unique 

 direction may also be determined from measurements of pressure and water 

 particle velocity along orthogonal horizontal axes or from measurements 

 of the wave height and surface slope along these axes. 



It may also be assumed that the wave energy at a given frequency is 

 distributed over a range of directions according to a formal law and to 

 use wave observations from an array of sensors to determine the coeffi- 

 cients in the selected law. It is important to note that the determina- 

 tion of wave direction by analyzing the records from an array of sensors 

 is necessarily based on an assumption about the law which governs the 

 distribution of wave directions. If the assumption is precisely correct 

 and there are no instrument or analyses errors, the information on wave 

 direction will be correct. If the basic assumption is incorrect, the 

 results of the analyses may be misleading even when there are no instru- 

 mental or data processing errors. 



Techniques for determining wave direction by analyzing the records 

 from an array of wave gages have been reported by Fuj inawa (1974), 

 Panicker (1971, 1974), Esteva (1977), and others. 



When an image of the wave field is analyzed, some trains of low waves 

 may be overlooked; however, if a wave is identified in the image of the 

 wave field, then that wave train must have been present on the ocean and 

 the direction determined from the image cannot be greatly in error. 



VII. DISCUSSION 



The CERC radar system was designed to automatically obtain images of 

 the wave field for measurement of wave direction and length. The system 

 also has the capability of determining wave speed, current speed and direc- 

 tion, information on refraction, and a potential of obtaining additional 

 information. 



1. Additional Capabilities of CERC Radar System . 



There are two situations in which the CERC radar system can be used 

 to measure wave period. If the radar is in the manual operation mode, 



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