approximately parallel to their optical axes. The stereoscopic over- 

 lap from the two cameras was triangular in shape as shown in Figure 2 

 and provided a workable area of approximately 30^,000 square feet„ 



The Zeiss ste re oplani graph was used again with the second 

 test photography. It was equipped with plotting cameras set to a 

 focal length of 204- nim. and rnatching the aerial caneras used for the 

 photography,, The original glass negatives which were exposed in the 

 aerial cameras were oriented in the stereoplanigraph plotting cameras^ 

 no prints being made. Using the exterior orientation data obtained 

 at the time of photo graphyj the overlapping exposures were oriented 

 in the instrument to form a stereoscopic model. As a result of the 

 methods used in the photography,, it was found that a stereoscopic 

 model resulted without undue difficulty and only very sli^t residual 

 parallaxes were encountered. The photographic quality of the model 

 was good and confirmed the result of the first test^ that wave forma- 

 tions could be observed and measurements could be made thereon. For 

 work in the near part of stereoscopic modelj a stereoplanigraph and 

 coordinatograph scale of ItlOO was used. For the more distant parts 

 of the model J a scale of 1;200 was used for the stereoplanigraph and 

 the scale of Is 100 was retained for the coordinatograph. 



Following orientation of the stereoscopic model, an attempt 

 was made to "contour" the wave formations which was the result 

 originally contemplated „ Contouring was found to be extremely slow 

 and difficult and of little value once obtained due to the irregular 

 nature of the wave formations , 



After the attempt at '^contouring** the wave forma tionSj a 

 method of measuring spot elevations was adopted. Elevations were 

 measured throughout the area of the usable overlap of the exposure s^ 

 these rraasureiTBnts being taken at arbitrary locations and at horizontal 

 intervals of approximately eight feet. The elevation values were 

 RBasured to 0,1 foot and were referred to the tide level at the time 

 of photography as a zero datura. The results of these measiirenBnts are 

 as shown in Figure 2, No difficulty was encountered in making these 

 measurements and it is felt that they are accurate to within 0,1 foot 

 although no check of this accuracy was possible. 



Discussion 



An examination of the msasurements recorded in Figure 2 shows 

 that some 905^ are positive value Sj, that is higher than tide level 

 at the time of photography^ and that the values range between -1,2 

 feet and + 3o4- feet. These results tend to indicate that measure- 

 ments were not secured in the bottom of the troughs. It is believed 

 that this is the case and that it is due to "masking" of the troughs 

 by the crests of the waves due to the very oblique angle at which 

 they were photographed. This condition was noted during the attempt 

 at contouring and is believed to be part of the reason for the com- 

 plicafcions encountered. As a result;, measurements were not secured 

 in the troughs and thus the wave heights could be determined only 



42 



