opposed to standard color film was hampered by the standard color film being 

 exposed in a camera with a 3-inch rather than a 6-inch focal length. Even 

 so, it was difficult to determine visually any significant difference in 

 resolution. 



The effect of sun angle on resolution was examined (Figs. 7 and 8). The 

 target was submerged to a depth of 40 feet and photographed with the 

 Wratten 57 filter. It was difficult to determine visually any difference 

 in resolution due to sun angle changes as long as the target was not in 

 the sunglint area. The main effect of varying sun angle was to increase 

 the area of the frame covered by sunglint. At the 56° and 71° sun angles, 

 the photographs taken with the 80-millimeter focal-length Hasselbad camera 

 and a 56-millimeter film format were almost entirely covered by sunglinto 



The effect of exposure on resolution was examined (Fig. 9). The target was 

 photographed at a depth of 40 feet with the camera set for one-stop under- 

 exposure, normal exposure, and one- and two-stop overexposure on four 

 successive overpasses. Normal exposure had been determined by a sequence 

 of test exposures made 1 month prior to the actual test program. The 

 exposure that gave the best contrast of bottom features was chosen for 

 normal exposure. Although the total film density varies for the one-stop 

 underexposure, normal exposure, and one-stop overexposure, the resolution 

 of the 4- by 12-foot bars on the target did not change. For the two-stop 

 overexposure, little could be seen other than the boat on the surface. 



The effect of aircraft altitude on resolution was investigated (Fig. 10). 

 Photographs were taken with the target submerged to a depth of 40 feet and 

 the aircraft flying at 2000-, 4000-, and 12,000-foot altitudes, using 

 Kodak 2405 film and a Wratten 57 filter. The target could be readily iden- 

 tified in both the 2000- and the 4000-foot-altitude photographs, but not in 

 the 12,000-foot-altitude photograph, due to the low contrast between the 

 target and the water so that the target is lost in the grain of the image. 

 The 4- by 12-foot bar was distinguishable in the 2000-foot-altitude photo- 

 graph, but was difficult to distinguish in the 400-foot-altitude photograph. 



The effect of using a polarizing filter was studied (Fig. 11) o Photographs 

 were taken from a 2000-foot-altitude with the target submerged to a depth of 

 30-feet. Both photographs were taken with Kodak 2405 film and a Wratten 57 

 filter, one with and one without a polarizing sheet. A polarizing filter 

 was oriented so as to cause a maximum reduction of glare from the water 

 surface. The camera was opened up two stops to compensate for the 

 polarizing filter. In both cases, the 4- by 12-foot bar was clearly 

 visible in the photographs. There was a slight indication of the 2- by 

 6-foot bars in the photograph obtained without the polarizing filter. 



The conclusions presented above are based on a visual analysis and are 

 consequently subjective. Analysis of the data by using isodensitiometer 

 readings on the original film and normalizing the readings to the control 

 target set up on the beach is in progress. This analysis will be performed 

 both on the underwater target and on selected natural features on the bottom 

 of Lameshur Bay. This instrumental analysis will eliminate the subjective 

 judgment and may modify the conclusions reached by visual examination of 

 the data. However, it is believed that only minor revisions of the following 

 conclusions will be necessary. 



VII-11 



