Comparisons of estimates of wave direction and wavelength (based on 

 radar photos with estimates from other imagery, including aerial photos 

 and gage records) generally show good agreement. 



Although the quality of radar imagery is not as good as that of aerial 

 photography, it has the advantage of being available at night and during 

 storms. Radar also permits images of the wave field to be collected in 

 the time-lapse mode and is less expensive than aerial photography. Radar 

 images have a distinct advantage over an array of wave gages as a source 

 of information on wave direction because the radar image provides visual 

 evidence of refraction (when present) and of the relation between wave 

 direction in the designated region and the surrounding area. 



The radar imaging technology in determining wave direction has some 

 distinct restrictions to be recognized if this technique is to be prop- 

 erly explored. 



The most fundamental limitation is the need to have ripples (at least 

 1.5 centimeters in length) coexisting with more prominent wave trains to 

 obtain sufficient signal return. However, a windspeed of 5 knots will 

 generally assure sufficient ripple formation. Thus, this condition is 

 usually satisfied in a growing wave field. 



The resolution of commercial radars is not adequate to ensure detec- 

 tion of wavelengths less than about 25 meters (83 feet) corresponding to 

 periods of 4 seconds in deep water. However, slightly shorter waves may 

 be distinguished on occasion. This restriction can be reduced by re- 

 designing some components of the radar system. 



The contrast between the appearance of the wave crest and wave 

 trough is greatest when the wave crest is high enough relative to the 

 radar antenna to shadow the following trough, but not high enough to 

 shadow the following crest. For most coastal locations an antenna 

 elevation between 10 and 20 meters is best, although a variable antenna 

 height could be more useful. 



The optimum console settings vary with the ambient conditions of 

 wind and waves. Some allowance for this factor has been made in the 

 CERC system by photographing the display scope with a series of ranges 

 during each observation. A median level for the other console settings 

 to achieve the best imaging in most conditions has been determined. 



Radar images generally indicate long-crested waves with character- 

 istics which change only slowly in time. A slight variability in inten- 

 sity and direction is apparent along each crest, but the general pattern 

 is usually stable. 



This report has shown that high-resolution imaging radar is a useful 

 tool in the study of waves in the coastal zone, and that this approach is 

 more useful than other alternatives for some applications. Many years of 

 research and development are required before most of the questions on the 

 use of imaging radar in the study of waves can be answered. 



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