were less than anticipated, the approach and 

 instruments are fairly representative of this 

 system and are described in reference (29). 



TRIESTE IVs interrogator consisted of a 

 transducer which transmitted a 7-kHz signal 

 and a receiver capable of receiving 10 replies 

 at frequencies between 12.5 and 17 kHz. The 

 interrogator receives, processes and digitally 

 displays three preselected frequencies as 

 slant ranges to the bathyscaph. The depth of 

 this operation was 12,000 feet and an area 

 500 X 800 feet was to be covered. 



The plan envisioned three ships simultane- 

 ously dropping three transponders buoyed a 

 short distance off the bottom to form an 

 equilateral triangle. TRIESTE II was then 

 to twice cross each line (base line) between 

 the transponders to establish the distance 

 between the three as pictured in Figure 

 10.26. Having established the dimensions of 

 the net and the relative bearings of one 

 transponder to the other, the bathyscaph 

 would then begin a controlled search interro- 

 gating on 7 kHz and receiving on 14.5, 15.5 

 and 16.5 kHz. In addition to the input from 

 the transponder interrogation system (called 

 TIP), data from a pressure transducer, Dop- 

 pler sonar and gyrocompass were also fed 

 into a computer which then allowed the 

 bathyscaph's progress to be displayed on an 

 x-y plotter. 



This approach is the optimum for a trans- 

 ponder system, but as so often happens in 

 the actual at-sea phase — the results were 

 quite different than anticipated. First, the 

 transponders were not dropped simultane- 

 ously. Next, only two out of the three worked 

 at first, which required the dropping of a 

 fourth. The subsequent operations over a 6- 

 week period consisted of on-again, off-again 

 transponder reception. In the final analysis, 

 TRIESTE was forced to use the one working 

 transponder and gyrocompass headings to 

 maneuver itself into the prime search area, 

 and then to navigate by use of SCORPIOIS's 

 debris. 



TRIESTE IFs experience sums up the ad- 

 vantages and disadvantages of bottom- 

 mounted acoustic systems probably better 

 than any other means: Operationally, the 

 potential is yet to be realized. This is not to 

 say that transponders or timed-pingers do 

 not work. ALVIN's aircraft search went off 



flawlessly, and transponder positioning sys- 

 tems have worked perfectly in other applica- 

 tions. But there are exceptions, and far more 

 often than not system complexity and the 

 dependence on so many factors result in 

 partial success. For these reasons contempo- 

 rary industrial operators of submersibles 

 have shied away from this approach. An- 

 other factor is cost; a commercial CTFM 

 sonar costs some $50,000, a transponder with 

 its acoustic release mechanism (necessary 

 for retrieval) is about $5,000. Consequently, 

 the initial outlay in funds for a three-trans- 

 ponder system with all the attendant elec- 

 tronics and processors can run to almost half 

 the cost of a small, shallow-diving submers- 

 ible — an example being thePC-J4 which cost 

 Texas A&M University approximately $145 

 thousand. 



Homing 



The term "homing" simply means going to 

 a specific location or an object. All of the 

 navigation schemes discussed in the preced- 

 ing sections can be used to home in or direct 

 the submersible to an object, site or what- 

 ever. In many instances it is not necessary to 

 know the geographic location, but merely to 

 find or reacquire the item of interest. There 

 are a variety of instruments and approaches 



BASE LINE CROSSING 



Rg. 10 26 Transponder (DOT) grid and base line crossings as originally planned tor 

 TRIESTE lis SCORPION operations. [From Ref (29)1 



512 



