Neshyba 



and is the range obtainable in the absence of external noise. 



Comparison of Laser Beam Scatter and Bioluminescent 

 Stimulation Lamp Intensity 



A question naturally posed is whether the Xenon stimulation 

 light intensity used in the luminescence experiments is equivalent to 

 the intensity of light scattered into a similar volume of water by a 

 laser mapper. Clarke and Hubbard (1959) have concluded that flashes 

 from organisms at ranges greater than about 8 meters are not re- 

 corded by a photomultiplier photometer of the type used. The fol- 

 lowing computations of the laser scatter are made for a point 10 

 meters off laser axis, as shown in Figure 3. 



The intensity of light scattered in a direction from the 

 propagation axis of a light beam is given by 



J (e) = HV <r(©) (10) 



Where J(©) is the intensity of scattered light in the direction ©, 



in microwatts per steradian, 



H is the laser beam flux per unit area on the volume V; for 



the model lidar, this is 5. 9xlO-'-'^ microwatts /cm^ at a point 



10 meters from source. 



V is the volume of the laser beam path element from which 

 scatter is computed; for the model lidar, this is taken as 

 1 cin-^. 



cr(©) is the volume scattering coefficient; a typical value of 



(r(90°) at 470 millimicrons for ocean water is 2 x 10""cm-l 



steradian" . 



Total scatter intensity in the direction p is found by integration over 



all such scatter volumes in the laser beam. A rough approximation 



to the integral, considering that 



(a)«"(©) is constant and conservatively taken as9'(90°), 

 (b) only scatter in the first 20 meters of laser path is 

 significant, then 



/©2 

 J(©)d© = 2. 4 x 10 microwatts /steradian. 



^1 (11) 



An analogous computation for the light intensity at p in the 

 field of the Xenon flash lamp is also sketched in Figure 3. For a 

 lamp output of 2 X 10° lumens peak and a reflector gain of 6, the 

 intensity is 



J =1x10 microwatts /steradian (12) 



p, xenon 



One concludes that a laser pulse would provide an equivalent volu- 

 metric stimulation coverage to that used in the luminescence exper- 

 iments. Since this volume coverage envelopes the instrument, so 



435 



