iNesnyba 



luminescent flash. Of importance to this discussion is the fact that 

 for rapid stimuli the response builds up, following the onset of the 

 train, to a level as much as 10, 000 times as intense as the normal 

 background level (Fig. le). This enhanced background level may be 

 sustained for several minutes, and decays slowly following cessa- 

 tion of stimuli. 



The engineer in designing underwater lidar will treat differ- 

 ently the two phenomena of flashes and of increase in background 

 level. For instance, the high intensity flashes may be discriminated 

 by either pulse width gating or by other "false alarm" type circuitry. 

 The background level is probably discriminated only through the use 

 of narrow band filters, and represents a more severe limitation to 

 receiver performance. In the following sections, the effect of these 

 noise-like sources upon the available range of a typical underwater 

 laser-powered optical device is examined. 



Specifications of a Model Underwater Lidar 



Consider a model lidar designed for use in ocean water, 

 having the general specifications: 



TRANSMITTER 

 Type 



Transmission 

 Pulse rate 

 Peak pulse power 

 Pulse length 



Wavelength 

 Power spectrum 



Antenna 



Beam width 

 Resolution 

 Scan method 

 Scanning angle 

 Strip scan rate 

 Velocity scan rate 



RECEIVER 

 Type 



Wavelength 



Q switched laser 



Pulse 



At least 1000 pulses /second 



1 megawatt 



-9 

 Dependent upon type: 2x10 seconds 



for Q-switched laser, others not spec-. 



ified 

 470 millimicrons 

 Monochromatic 



6 " telescope 



0. 4 milliradians, circular 



20 cm. diameter @500 meters 



Strip map 



t 40° vertical angle 



40° /second 



8 cm per second ground speed 



Photomultiplier 



Dependent upon photocathode material 

 For S-11 phosphor, the wavelength of 

 peak response is 440 millimicrons 



430 



