APPENDIX A 

 PROCEDURE FOR ANALYSIS OF STEREOPHOTOGRAPHS 



SELECTION OF PHOTOGRAPHS 



Many hundreds of stereophotographs were taken during the sea trials of the VALLEY 

 FORGE and the UNIMAK. Since a photogrammetric analysis of each photograph is time- 

 consuming and expensive, a limited number were selected for analysis. The purpose of the 

 stereo analysis was (1) to provide quantitative data against which the visual estimates of 

 trained observers could be checked and (2) to provide a quantitative measure of the sea con- 

 ditions for correlation with simultaneous measurements of the ship's response to the sea. 



Of the many stereophotographs available, sixty were selected for analysis; see Table 4. 

 The selection was made to satisfy both the requirements just stated and to cover as wide a 

 range of sea conditions as practicable. The accuracy of a wave profile varies with the dis- 

 tance from the camera to the profile. The average accuracy is about - 0.5 ft at a distance of 

 2000 ft and is better than this at shorter distances. 



ANALYSIS OF STEREOPHOTOGRAPHS 



Each of the selected pairs of stereophotographs was converted into sea surface profiles 

 by photogrammetric specialists at the Naval Photographic Interpretation Center and Navy Hy- 

 drographic Office. The Wild A5 Audograph and Zeiss Stereo Planigraph Model C5 were used 

 by the respective agencies, and vertical mapping techniques were adapted to this horizontal 

 application. Next the sea surface profiles were analyzed by the Oceanographic Division of 

 the Hydrographic Office. The procedures devised for this analysis are given in the following 

 sections. 



PROFILE DETERMINATION FROM STEREOPHOTOGRAPHS 



Sea surface profiles were determined from the stereophotographs by the following pro- 

 cedure: 



1. Draw the first profile at a distance not less than 250 ft from the camera stations. 



2. Draw successive profiles at increments of 125 ft. 



3. Draw as many profiles as possible. The profiles should be approximately 1 in. apart 

 on the manuscript. 



4. Maintain the horizontal scale constant. Give horizontal scale factor. 



5. Exaggerate the vertical scale (wave heights) as much as possible. Give the vertical 

 scale factor. 



6. Use number at the left of the profile to indicate the distance from camera station in feet. 



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