target-position data into equal-elevation sets. Feeding 

 these sets, successively, to an X-Y plotter would then 

 yield the usual type of contour map. With optical 

 stereo pairs in front of the projectors, this final 

 sorting process is unnecessary because the operator 

 directly plots equal-elevation points as he constructs 

 the map. 



The brute-force procedure is to directly measure 

 Rj and R2 without using a stereo-projector/computer 

 system (such as in Figure 2); but the assumption is, 

 and has been from the beginning of this investigation, 

 that the stereo-viewing approach will be faster and 

 less expensive. This assumption is based on the reason 

 used in stereo-photo plotting: it is easier to match 

 corresponding target points by stereoscopic viewing 

 than by (1) looking at the separate images, (2) 

 picking out what appear to be matching points, and 

 (3) making measurements directly on the image sur- 

 face with a calibrated scale. 



Hence, provided system errors are under a 

 specified magnitude, the practical value of stereo- 

 sonar contour mapping by stereoscopic viewing 

 depends on how photographic we can make the 

 images. The sonar-pair images must blend together in 

 such a way that there is an insignificant probability of 

 matching images which do not correspond. The 

 image-definition problem is as important as the fish- 

 vector measurement problem. Even with infinite 

 precision in the measurement of B and the fish 

 positions in a shore-based reference frame, if the 

 imagery cannot be fused into a three-dimensional 

 illusion, stereo plotting is not workable. 



SEA TRIALS 

 Sonar Equipment 



The towed sonar system consisted of two 

 side-looking sonar fish operated through a dual- 

 channel transceiver/recorder having a wet-paper chart 

 readout. Each sonar fish was a Klein Model 402A, 

 shown in Figure 3 on board the towing vessel. The 

 deck equipment was a Klein Model 401 recorder 

 (Figure 4) and a specially built auxiliary unit for 

 operating both fish simultaneously. 



Each sonar fish was operated at 100 kHz and up 

 to a maximum of 10 pps with pulse length of 0.1 

 msec. The two-fish system, including two 300-foot 



electromechanical cables, was furnished under a lease 

 agreement with Klein Associates, Inc., Salem, New 

 Hampshire. 



Tow System 



A schematic of the tow system is shown in 

 Figure 5. A 42-foot, 2-inch-diameter steel pipe was 

 attached to the stern of an LCM-8 and stabilized by 

 lines connecting the ends of the pipe to the gunnels 

 and the wheel house. The starboard section of this 

 outrigger system is shown in Figure 6, with the fish 

 under tow. Towing speed was held at approximately 

 2 knots. 



The required tow-cable lengths were estimated 

 for the desired depths and trailing distances of the 

 two fish. The estimates were based on assumed values 

 of hydrodynamic parameters, such as drag and cable 

 buoyancy. The Klein electromechanical cable, having 

 an outside diameter of 3/8 inch and utilizing a fiber 

 glass strain member, was used for towing and signal 

 transmission. After the required towing lengths were 

 calculated, each cable was tied to the outrigger pipe 

 as shown in Figure 6; and the excess cable was 

 wrapped around a gunnel bitt and coiled on deck. 



Stereo-Sonar Operations 



All of the stereo-sonar data were obtained at 

 two near-shore areas. One area in the vicinity of CEL 

 was about 2.5 nautical miles offshore with a depth of 

 about 100 feet. The other area, just outside the surf 

 zone at the Carpinteria beach about 22 nautical miles 

 up the coast from CEL, had an average depth of 

 about 25 feet. 



Because the 100-foot-depth seafloor area near 

 CEL is essentially featureless, an array of artificial 

 sonar targets was implanted. Four reflectors were 

 spaced about 500 feet apart, connected by a bottom- 

 lying 1-inch-diameter wire rope. Each reflector was a 

 2,600-pound concrete block to which was attached a 

 buoyant 3 5 -inch-diameter aluminum sphere. A 

 schematic of the array is shown in Figure 7. 



The 100-foot-depth area was chosen to permit 

 same-side stereo scanning with maximum bottom 

 coverage. The tow-cable lengths were adjusted to pro- 

 duce the geometry shown approximately in Figure 8. 

 Tow-cable lengths for fish no. 1 and no. 2 were 

 adjusted to 80 and 20 feet, respectively, yielding 

 depths of roughly 30 and 20 feet, respectively. 



