Perhaps the best example of a presently available sonar unit with 

 unclassified performance parameters is the AC-DRL Acoustic Guidance Sonar 

 (AGS) J^ The AGS is a high-resolution, echo-ranging sonar system capable 

 of locating and displaying acoustically reflective submerged objects at ranges 

 from less than 1 foot to 1 ,500 feet, in water up to 20,000 feet deep. Uses 

 for the AGS include: 



1. Reentry operations 



2. Pipeline surveys 



3. Bottom search and recovery operations 



4. Object location and avoidance foriunmar^ned submersibles 



A noteworthy advantage of the AGS system is that it can locate and 

 display passive underwater objects. Devices such as beacons or transponders 

 are therefore unnecessary, so the reliability and cost of these items are of no 

 concern. Because the unit is self-contained, it can be used on any vessel or 

 vessels. Moreover, since there is no need to mark the targets, it can be used 

 to locate and identify any conceivable type of underwater structure at any 

 time. 



The resolution of this unit is exceptional and definitely would be of 

 use for underwater positioning and guidance for near-future uses. For 

 example, it would be possible to locate an object 6 inches on a side, 

 1,500 feet from the sonar scanner. An example of this high resolution is 

 shown in Figure 17; the important features of Figure 1 7 are explained in 

 Figure 18.^° Figure 17 is a time exposure of the display of the AGS during 

 a test in a 10-foot diameter wooden water tank at a depth of 10 feet. 

 Noteworthy is blip No. 3, which is the sonar reflection from a No. 8-32 

 flathead wood screw, 1/4-inch long, and at a slant distance of approximately 

 4 feet. Assuming the pipe string supporting the sonar unit could be differen- 

 tially controlled, it appears that the system could close on an object of this 

 size — perhaps starting from as much as 1 ,500 feet away. An optical system 

 could and most likely would be desired at this range. Nevertheless, there is 

 sufficient evidence to conclude that even off-the-shelf sonar units such as the 

 AGS are more than adequate for locating small objects. Indeed, it appears 

 that the problem is really one of taking advantage of these sensitive sonar 

 systems, since at the present time there is no efficient technique for 

 effectively controlling either the sonar or, if need be, the target. Thus, the 

 problem is one of designing the mechanical subsystems — the electronics 

 are already more than adequate. 



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