Repeatability Of Common Uxo Detection & Discrimination Instruments

Abstract

In support of UXO detection and discrimination, considerable effort has been and is being devoted to (1) understanding the operating characteristics of currently deployed EMI sensor systems, (2) characterizing the sensor system response as a function of location of a given ordnance target relative to the system, (3) characterizing the sensor signatures of given EMI systems to a wide variety of ordnance types, and (4) currently an effort to characterize the variation in signatures of given EMI sensors with a statistically significant sampling of representatives of the same ordnance type. Complementary to the fourth item, there has not been a similar effort to characterize and understand the signature variation to a given ordnance item among various geophysical systems of the same type. Even differences in the 5 to 10 % range between the same type systems over a given ordnance item, while perhaps insignificant from the perspective of detection, could lead to erroneous classification/identification from the perspective of discrimination. Production geophysical surveys for UXO detection and discrimination typically use two technologies: electromagnetic induction (EMI) systems and total field magnetometry (TFM). EMI systems are the most versatile of the geophysical methods used for surveys for buried UXO, leading to environmental restoration. The EMI systems are versatile due to the capability of broad bandwidth operation and variable transmitter and receiver configurations. TFM sensors are the most reliable and simplest systems to operate while also having the ability to detect large targets at greater depths than EMI. One new unit, if possible, of each of the three most common instruments used in UXO remediation projects: the Geonics EM61-MK1 and EM61-MK2 metal detectors, and the Geometrics G-858 magnetometer; were tested as reference instruments. The response of the instruments was monitored as a function of time versus the following parameters: battery voltage, system current draw, transmitted power (where applicable), electronics temperature, battery temperature, and ambient weather conditions. The measurements have been repeated multiple times in one day as well as on subsequent days while using a regulated power supply to attempt to determine which parameters have the most significant affect on system response. Currently we have tested four EM61-MK1 units, two EM61-MK2 units and two G-858 units. A total of ten units of each type will be tested for this project. The surprising result that has been observed is that the signal to noise ratio of the EM61 series instruments is a function of the battery voltage, which indicates that the transmitted current is not regulated.