EVALUATION OF FACTORS AFFECTING RESOLUTION 

 OF SHALLOW-WATER BOTTOM FEATURES 



Dr. Curtis C. Mason, Dr. Dean R„ Norris, and Ivan D. Browne 



NASA Manned Spacecraft Center 



Houston, Texas 



ABSTRACT 



A specially designed underwater resolution target was photo- 

 graphed from an aircraft equipped with 3- and 6-inch focal- 

 length cameras. The target was positioned at depths from 

 5 to 60 feet and photographed from 2000-, 4000, and 12,000- 

 foot altitudes, with sun angle varying from 34° to 70° and 

 exposure varying from one stop underexposed to two stops 

 overexposed. Seven filter combinations and five film types 

 were used. A visual inspection of the photography indicates 

 Kodak SO-397 color Ektachrome file and Kodak 2405 high-speed 

 Panchromatic film (black and white) with Wratten 2E and 47, 

 Wratten 57, and Wratten 21 and 57 filters gave approximately 

 the same results, and were better than other filter-film 

 combinations. Varying optimum exposures plus or minus one 

 stop had little effect on resolution. At a 5-foot submergence 

 depth, 1- by 3-foot bars could be easily resolved. At a 

 15-foot submergence depth, 2- by 6-foot bars were separable. 

 At a 30-foot submergence depth, 2- by 6-foot bars were visible. 

 At a 45-foot submergence depth, 4- by 12-foot bars were clear 

 and sharp, and at a 60-foot submergence depth, 4- by 12-foot 

 bars were becoming faint. With the target at a 40-foot 

 submergence depth, sun angle had little effect, as long as 

 the target was not in the sunglint area. 



OBJECTIVE 



To determine the effects of factors such as submergence depth, sun angle, 

 film and filter type, exposure, aircraft altitude, and polarization on the 

 photographic resolution of an underwater object. 



PROCEDURES 



A specially designed target (Fig. 1) with resolution-bar dimensions of 4 by 

 12 feet, 2 by 6 feet, 1 by 3 feet, and 1/2 by 1-1/2 feet was used to eval- 

 uate the effects of t;he parameters mentioned previously on underwater 

 resolution. Divers from the TEKTITE project were used to develop target 

 deployment techniques. For data collection, divers from the Cape Fear 

 Technical Institute Research Vessel ADVANCE II positioned the target at 

 depths ranging from 5 to 60 feet below the surface in the clear water in 

 Lameshur Bay, St. John Island (Fig. 2). 



The buoyant 12- by 24-foot target was positioned at the proper depth by four 

 winches mounted at the corners of the target, and was fastened by cables to 

 weights positioned on the bottom. The target was photographed from an 



VII-4 



