In preparation for these tests, an underwater search range consisting of 1-1/2-inch chain, 

 3-1/2-inch armored cable, and twin 90 steel tanks was prepared in about 35 feet of water. These 

 targets were buried in sand approximately 30 feet apart from each other with floats attached for 

 identification. The targets were buried by fluidizing the soil around the target with a jetting 

 nozzle. Burial depths were estimated by measuring between the surface of the sand and 

 reference marks on Uie float line. 



The test procedure consisted of swimming the range with the metal detecting device and 

 searching each target location. At sites where a target was located, the maximum detection 

 distance was estimated by raising the sensor above the target until its detection threshold was 

 reached. The detection depth was estimated by adding the distance between the sensor and the 

 seafloor to tiie burial depth of the target (estimated from the tape marks on the float line). 



In addition to these tests, the Forster Ferex was used in the dipping mode to assess this 

 operating scenario. During these tests, the Ferex was used from an inflatable boat with the probe 

 submerged to within about 10 feet of the bottom. The distance off the seafloor was estimated 

 by periodically lowering the probe until slack appeared in the cable. 



Results of the detection tests are shown in Table 3. Detection thresholds from the TEMP 

 are also listed for comparison. These tests show the following: 



1 . The detection ranges of commercially available pulse-induced systems cannot meet 

 the detection tiiresholds of the TEMP. In addition, several serious deficiencies were noted for 

 each system. These are as follows: 



a. Garrett XL500 - Although this unit out-performed the other pulse-induced 

 systems, it did not have the ruggedness required for UCT operations. During these tests the arm 

 rest bracket broke off. In addition, the meter display was small and difficult to view. The 

 headphones were awkward to wear and had a tendency to slip off the head. The sound was also 

 muffled significantiy when the headphones were worn over a diving hood. 



b. Fisher Pulse 8 - This unit was difficult to zero (adjust to background 

 interference) because of the 2-second response time of the electronics. Proper adjustment of the 

 zero is important for optimum performance. If the zero is overadjusted, then the unit becomes 

 too sensitive and is susceptible to the detection of small, insignficant items. If the zero is 

 underadjusted, then the sensitivity of the unit is decreased, thereby decreasing the detection 

 distance. Once properly adjusted, the slow response time requires that the unit be moved very 

 slowly to avoid missing a target. In addition to the zeroing problem, the unit was awkward to 

 handle because the front end "planes" from side to side. This is because the front-end housing 

 of the sensing coil is shaped in a solid disk and therefore presents resistance to forward motion. 

 This motion further compounds the problem related to the slow response time of the electronics. 



c. White's PI- 1000 - This unit could not be zeroed during these tests. 

 Subsequent inspection of this unit indicated that the detent mechanism on the main switch was 

 either broken or worn at the position for tuning/zeroing the unit. No further tests were 

 conducted with this unit since it generally lacks the integrity and ruggedness required for UCT 

 use. 



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