HUMAN BEHAVIOR PROGRAM 



251 



WHITE BLACK WHITE YELLOW 

 SQUARE DISK CROSS TRIANGLE 



Fig. 103. Arrangement of Sealab U 

 form/color visibility range 



Four targets were used; a white square, a black circle, a white cross, and a yellow trian- 

 gle. The size, area, and experimental arrangement of the targets is shown in Fig. 103. Each 

 target was mounted on the end of a piece of black channel iron. A specially marked surveyor's 

 tape was layed on the bottom, so that the zero end of the tape was directly in front of the line 

 of targets. The test was conducted as follows. Two divers swam to the 48-ft mark on the sur- 

 veyor's tape, faced the line of targets, and proceeded to swim slowly toward them. The task of 

 the divers was to note independently at what distance they could detect the targets, and at what 

 distance they could positively identify the form. Extreme care was taken not to kick up the mud 

 on the bottom. The tests were taken far enough from the habitat that only ambient light fell on 

 the targets. The observations were made at various times of the day, ranging from 10:00 in 

 the morning, until 6:00 in the evening. Most of the observations were taken around noon. Six 

 different observers were used in this experiment. A total of 20 observations on each target 

 was obtained. 



Visibility Studies — The Sealab 11 program provided one of the few opportunities to collect 

 data on the optical characteristics of sea water simultaneously with human visual data. Each 

 diver was required to estimate the distance at which he could see the lights of the habitat, as 

 well as individual diving lights. 



An Inshore Water Clarity Meter, developed by the Scripps Institution of Oceanography, was 

 used during the submergence of Teams 2 and 3. This is an instrument for measuring scalar 

 irradiance and the attenuation coefficient at sea. The instrument can produce profiles of sca- 

 lar irradiance at depths to 500 ft. During Sealab II it was lowered by cable to a depth of 180 ft. 

 The data, which include a measure of incident light falling on the surface of the sea, is auto- 

 matically recorded. Whenever possible, readings were taken during the same time intervals 

 that visibility and form/color discrimination tasks were performed. This test is of great im- 

 portance, as it is the first time that perceptual measurements have been made concurrently 

 with optical measurements underwater. The results of such tests should enable us to predict 

 more accurately visibility ranges for operational purposes from measurements made using a 

 Water Clarity Meter alone. 



