level does not change significantly when the unit is moving over a target (unless the probe is 

 moved very slowly over the exact magnetic center). By comparison, the meter located on the 

 control instrumentation swings from one extreme to the other (i.e., positive to negative) when 

 the sensor is moved over a target. This provides clear indication of the target location. 



Results of the dipping test indicated that the Ferex used in this mode of operation 

 provides a system for general location of targets. This feature is clearly beneficial since it can 

 minimize diver time in the water. For use in this mode, the Ferex must be used at high sensi- 

 tivity levels since it is towed with the probe approximately 10 feet off the bottom. This requires 

 that a maximum distance be maintained between the probe and the boat since the boat can be a 

 significant magnetic target at high sensitivity levels. It was also noted that there is a tendency 

 for excess cable in the boat to become tangled and knotted. Snarling and entanglement of cable 

 in a small boat is a nuisance and a safety hazard, and can also result in damage to the electrical 

 conductors in the cable. 



As shown in Table 3, the TEMP thresholds for detection of an anchor (6,000 pounds) 

 buried to 10 feet and armored pipeline (5-inch diameter) buried to 2-1/2 feet were not tested with 

 these systems. Based on the results of the laboratory and ocean tests, it appeared unlikely that 

 the pulse-induced systems in their current off-the-shelf form would meet these requirements. 

 However, the Forster Ferex appeared to have the capability for detecting these items. Table 4 

 shows the magnetic signature of SD cable (list 5), armored pipe (5-inch diameter), and a 6,000- 

 pound anchor at 5 feet, 4-1/2 feet, and 12 feet, respectively (Ref 1). Based on this information 

 and the results of the ocean tests, it appeared highly likely that the Forster Ferex could meet 

 these TEMP thresholds. 



Table 4. Magnetic Signatures of SD Cable, 5-Inch Pipe, and 6,000-Pound Anchors 



Object 



Burial Depth (ft) 



Sensor Distance (ft) 



Magnetic Signature 

 (t) 



SD List 5 



3 



5 



291 



5-Inch Pipe 



2-1/2 



4-1/2 



257 



6,000-Pound Anchor 



10 



4-1/2 



3,055 



Conclusions and Recommendations from the ADM Tests 



1. Commercially available pulse-induced systems cannot satisfy the performance 

 requirements of the TEMP. Increasing the detection thresholds may be possible by modifying 

 these systems to incorporate a more powerful system with a larger sensing coil. 



2. The Forster Ferex magnetometer had the greatest detection distance among the 

 units tested. Modification of this unit holds the most promise for providing a metal detecting 

 system suitable for UCT use. 



15 



