Neshyba 



to speak, the case is strong that the optical receiver will record the 

 bioluminescent response to such stimulation. K the velocity scan 

 speed of the submersible exceeded 10 meters per 1. 5 to 2. seconds, 

 the receiver would then pass out of effective range of the luminescent 

 organisms before they achieved their peak response. Such speeds 

 would be feasible for a bottom mapping lidar only if the pulse repeti- 

 tion rates for the laser could be at least 80, 000 pps. Lasers having 

 this high a pulse repetition rate at one megawatt peak pulse power 

 have not yet been built. 



Effective Bioluminescent Radiation in the Mapping Receiver Aperture 



It is assumed that the biological organisms responsible for 

 the stimulated response are uniformly distributed. The lidar receiver 

 at any one instant will see only a portion of the volume from which 

 the background radiation emanates. Computations have been made 

 which show that the volume coverage by the inapping receiver is only 

 about 7 X 10" of the volume sampled during the bioluminescent ex- 

 periments. Considering that the maximum bioluminescent median 

 background power density obtained during blue- green stimulation 

 (Neshyba, 1967, in press) is 1 x 10" microwatts /cm , then the power 

 density effective as noise background at the receiver optical aperture 

 is 



(1 X 10"5) X (7 X lO"'*) = 7 X 10" ® microwatts /cm^ (13) 



Useful Mapping Range in the Presence of Stimulated Bioluminescence 



In Figure 2, the effective bioluminescent noise power density 

 is plotted as point n' on curve (a). It is concluded that the useful 

 mapping range of the lidar system is now limited by the stimulated 

 noise background, and not by the inherent noise internal to the lidar 

 itself, to about 230 meters. 



Use of a Narrow- Band Filter in the Receiver Optics 



Since the bioluminescent spectrum is broad, it is worth- 

 while to examine whether range performance can be bettered by in- 

 corporating a narrow band-pass filter in the receiver optics. A 

 filter having a 10 Angstrom (1 millimicron) pass band centered at 

 470m|j,, and a transmittance of 10% is selected here; the correspond- 

 ing range curve for the modified receiver is shown as curve (b) in 

 Figure 2. 



Bioluminescent spectra are not well known. Clarke (1962) 

 states that the lantern fish emit 80% of their energy in the range 

 450-550 millimicrons. Assuming their energy uniformly distri- 

 buted in this band, the spectral irradiance of bioluminescence is 

 then given by 



437 



