Comparison of Minimum Detectable Light Levels and the 

 Level of Stimulated Marine Bioluminescence in Ocean Waters 



Steve Neshyba 

 Oregon State University 

 Corvallis, Oregon 



The development of the Laser light source has given new 

 impetus to the study of ways by which man might extend his visual 

 reconnaissance of the oceans. One factor in the design of a Light 

 Detection and Ranging (Lidar) system for use in the marine environ- 

 ment is that bioluminescence can be a spurious signal; further, this 

 luminescence may itself be altered in the presence of laser trans- 

 missions. The engineer designing underwater lidar should recog- 

 nize that the optical receiver must obtain information while immersed 

 in a biologically active source field. Such a factor is wholly absent 

 in the design of atmospheric radar; its analogy could be that of a sky 

 full of tiny, floating, organically live transmitters whose output level 

 changes when the radar attempts to "look through" them. 



The Stimulated Bioluminescent Field 



Measurements have been made of the in situ bioluminescent 

 field when the organisms are subjected to trains of vari-colored light 

 pulses. A photomultiplier bathyphotometer and a Xenon flashtube, 

 both controlled from a deck recorder unit, comprised the in situ de- 

 vice which was lowered to a depth of 700 meters. The flashtube was 

 commanded to emit trains of 1 millisecond pulses, through selectable 

 color filters, at repetition rates of from 6 to 25 ppm, and the lumi- 

 nescent response recorded on deck. Details of the apparatus, along 

 with a discussion of the measured response to the several colors and 

 rates of stiinuli, are given by Neshyba (1967, in press). In general, 

 the response is positive to trains whose repetition rate is at least 

 6 ppm, with maximum response to green, blue, and white light 

 stimuli. Figure 1 shows the type of response usually measured. The 

 response to stimuli above the threshold rate usually reaches a peak 

 at 1. 5 to 2. seconds following the stimulus but decays at a slower 

 rate. Such response is readily distinguished from the normal 



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