On June 25, 1998, we performed a second set of tests at Fort AP Hill. On this trip, we were hosted by Tim Schweitzer and Ken Strittmatter from the Mine Neutralization group at Fort Belvoir. Prior to our trip, Tim and Ken prepared a mine lane for our tests. They added clutter to a set of anti-personnel mines that had been buried earlier in a mine lane at AP Hill. In all, the mine lane contained 23 objects, the location of each marked with paint on the soil directly above it. We made our way through the mine lane twice, each time taking three to six measurements on each object buried in the lane. After completing the second run-through, Tim and Ken revealed the identity of each of the 23 objects.
This test differed from previous ones in two principal ways. First, this was the first test we had performed that was truly blind, in which we knew neither the nature nor the location of any of the test objects. Second, this was the first test we had performed on landmines located in reconsolidated soil. In other words, these mines had been buried for a significant amount of time prior to our test, creating a more realistic test environment than our previous tests.
As we proceeded through the lane, we used the measurements from the device and our own senses to guess the identity of each object. Our guesses as to the identity of two of the objects differed on the two runs; for the other 21 objects, our guesses were the same on each run. Our guesses fit into the broad classifications of plastic mine, hard object, or soft object. Here are the results from the two runs:First Run
mines detected: 6/8 hard objects detected as mines: 2/8 soft object detected as mines: 5/7Second Run
mines detected: 8/8 hard objects detected as mines: 2/8 soft object detected as mines: 5/7NOTES
The main problem with the device was the high number of false alarms when testing "soft" objects such as wood sticks. In its different stages of development, the acoustic probe has always been more successful in distinguishing mines from harder objects such as rocks and metal than from soft objects such as wood. However, the high rate of false alarm seen in these tests is a new phenomenon. Given the change in the severity of this problem between previous tests and this one, it is possible that changes to the mechanical part of the probe prior to this test might be responsible for the increased rate of false alarm.
Due to its blind nature, this test gave us a better feel for the process of mine discrimination in the real world. We found that our own demining senses led us to the same conclusion as the acoustic probe for the majority of the trials. It is hard in non-blind tests to understand the significance of the deminer's experience in distinguishing a landmine from a clutter object. But having completed this test, the most realistic test we have performed, it seems that personal experience is as powerful a tool as the acoustic probe. If this is true, then it does not make sense for deminers to equip themselves with an acoustic probe. Only a significant increase in information provided to the deminer can offset the cost, complexity, fragility, training and additional support required by an automated discrimination device.