Figure 7. Schematic of artificial target array. 



Figure 8. Geometry of same-side stereo scanning 

 at 100-foot-depth site. 



horizontal component of this extent was, however, 

 not feasible. Analysis of outrigger statics and 

 dynamics showed that a 42-foot length was the ma.xi- 

 mum tolerable.'^ 



The other near-shore area, just beyond the surf, 

 was chosen because of the abundance of prominent 

 rock outcroppings. Although low-flying stereo 

 scanning was required, with its attendant problems of 

 grounding probability and error propagation, it was 

 believed that the highly contrasted imagery would 

 demonstrate the feasibility of fusing sonar charts into 

 a three-dimensional illusion. 



RESULTS OF SEA TRIALS 



The sea trials covered a period of 6 days, during 

 which 15 hours were actually devoted to stereo 

 scanning. Out of these 15 hours, about 3 hours 

 yielded data which appeared to be usable in 

 Equations 1 through 5. The data were those image 

 points on the sonar charts which were recognizable as 

 either the artificial targets, including the bottom-lying 

 wire rope, or a rock outcropping. 



The remaining 10 hours of sonar scanning 

 yielded imagery which did not contain clearly 

 identifiable targets. Most of this data resulted from 

 the existence of sea state 1 or greater during that 

 time. From the sonar-chart readout and direct obser- 

 vation of outrigger and tow-cable motion during sea 

 state 1 or greater, it was estimated that vertical 

 motion of either one of the sonar fish was in excess 

 of 4 feet, peak-to-pea-k. At the 100-foot-depth site, 

 with approximate sea state 0, peak-to-peak vertical 

 motion of an individual fish appeared to be under 4 

 feet, and imagery was produced in the sonar readout 

 which could be blended into a three-dimensional 

 illusion. Figure 9 shows a section of stereo-sonar 

 imagery of the 100-foot-depth target array for sea 

 state 0. 



Table 1 gives the results of 10 side-looking 

 stereo sweeps at the 100-foot-depth site. The maxi- 

 mum possible number of measurements on a given 

 sonar reflector is five. Crosstalk and mutual inter- 

 ference effects were minimized by using different 

 tow-cable lengths and, thus, staggering the two fish 

 out of each other's beam. 



A sea test was conducted to see if a pair of manned small boats could be towed at a constant separation of 50 feet. 

 With a tension line between the two boats, their separation could be held constant in a harbor tow; but, in the open 

 sea, even small-wave action made it impossible to maintain a constant lateral separation. 



Long sections of the 1-inch wire rope are clearly discernible in the sonar charts. Because of the high resolution and 

 contrast of the wire-rope imagery, three-dimensional blending is possible. However, the resolution of the sphere- 

 block targets was not sufficient to yield three-dimensional imagery. 



