Most wave gages record the time history of some property of the wave 

 at a fixed point, or a very small area, over a finite time interval, 

 usually about 20 to 30 minutes. When an array of gages is used to deter- 

 mine wave direction, it is necessary to postulate an analytic function 

 which describes the geometry of the sea surface and to determine the 

 coefficients in this function from gage measurements. 



Measurements from a single gage generally represent some type of 

 time average. When arrays are used, space-averaging based on discrete 

 points is also involved. 



Both types of data yield information on waves, but the information 

 revealed by different procedures is not identical because each observa- 

 tion technique concentrates on one or two facets of wave behavior and 

 neglects others. Exact agreement is not to be expected. Nevertheless, 

 the comparisons discussed in this section reveal a significant level of 

 agreement . 



The primary source of comparison data was the West Coast Experiment 

 (sponsored by National Aeronautics and Space Administration (NASA)) con- 

 ducted during February and March 1977 off the coast of southern California 

 (Shemdin, Inman, and Blue (1977)). The objective of the CERC participa- 

 tion in this experiment was to conduct a field shakedown test of the first 

 prototype CERC radar system, which had only recently been assembled, and 

 to validate as many CERC radar measurements as practical. Certain factors 

 prevented the CERC system from performing in an optimum manner. The 

 limited time for deployment and the available locations for operation 

 did not allow ideal antenna elevations. A subsequent discovery indicated 

 that the radar was not properly tuned and that misadjustment of pulse 

 width may have given a pulse as wide as 150 nanoseconds, three times the 

 desired value. This would have resulted in the radial resolution being 

 degraded from about 10 meters to between 30 or 40 meters (98 or 131 feet) . 

 However, radar wave images were produced which provided wave direction 

 measurements to compare with measurements from other instruments operating 

 simultaneously. These comparisons along with some information gathered 

 during an earlier experiment at Cape Cod are discussed below. 



1. Comparison with Aerial Photos . 



During the West Coast Experiment in March 1977, several U-2 aerial 

 photo missions were flown off the California coast in the area of San 

 Diego. Simultaneously, radar images of the waves were obtained with the 

 CERC radar system located at Mission Beach, San Diego. Two cases exist 

 where photos (as shown in Fig. 2) could be compared with radar images. 

 In these cases, measurements were made of the directions of propagation 

 for long-crested wave trains detectable on the radar image and the U-2 

 photos. Figure 2 shows a part of the aerial photo taken 29 March; Figure 

 32 shows a photo taken 14 March. The results are shown in a Table. The 

 CERC radar images and the U-2 photos were both taken within a 10-minute 

 period on each of the two dates. Wave measurements on the imagery were 

 made either at the U.S. Navy Undersea Center (NUC) tower at a depth of 



35 



