Attempts to identify buried objects using conventional geophysical survey data have produced uniformly unsatisfactory results. The problem is that classification based on dipole inversion of mapped survey data is intolerant of even centimeter-scale positioning errors in the data, and the technology for geo-location of survey data cannot provide the required positioning accuracy.
As originally envisioned, this project sought to demonstrate improved procedures for target classification with EM61 survey data using schemes that are tolerant of the positioning errors. Several procedures were tested with EM61 data from the ESTCP Classification Demonstration at the former Camp Beale in California. They showed no improvement in classification performance over the results using standard processing techniques.
Consequently, the project was re-directed to consider classification performance using survey-mode data collected using an advanced man-portable (MP) electromagnetic induction (EMI) sensor array recently developed by the Chemistry Division of the Naval Research Laboratory and SAIC. The success of the MP system for cued target identification in the Camp Beale demonstration was the primary motivating factor for adapting the system for dynamic or survey mode operation in this project.
The objective of this demonstration was to validate the performance of the MP system used in dynamic survey mode in a blind test at a live site—the former Spencer Artillery Range in Tennessee. Performance metrics included production rate, detection performance, percentage of targets classified using survey data, and classification performance.
The MP system comprises a square array of four transmit (Tx)/receiver (Rx) coil pairs mounted on a cart. The transmit coils are wound around the outer portion of 35-cm square Styrofoam forms. The three-axis receiver cubes are wound on 8-cm wooden blocks. The transient electromagnetic (TEM) and data acquisition electronics are in the backpack worn by the MP cart operator. Data acquisition is controlled by the tablet computer carried by the person walking beside the operator.
For dynamic survey mode operation, this demonstration used a decay time (and corresponding transmitter on time) of 2.77 milliseconds (ms). A base time period of 33 ms was used so that three repeats per transmit waveform could be averaged. Gate width was set at 20%, resulting in 19 time gates with center times ranging from 25 microseconds (μs) to 2.5 ms.
The demonstration was conducted as part of the ESTCP Live Site Demonstration at the former Spencer Artillery Range during May 2012. The dynamic test area covered 0.5 hectare (Ha) of open field. The classification was conducted for 339 unknown anomalies detected within the Dynamic Area. Approximately 70% of the detected anomalies could be classified from the dynamic data alone. Using a combination of results from dynamic data and cued data, 100% of the identified unexploded ordnance (UXO) were correctly classified and the number of necessary digs could be reduced by at least 75%.
This project demonstrated a UXO classification process that made use of dynamic mode data collection with an advanced EMI sensor. The data collected with these systems can be used both for anomaly detection and for classification on a significant fraction of the detected anomalies, limiting the number of anomalies requiring further investigation in cued mode.
Transitioning these technologies from research prototypes to use in the industrial community, where appropriate, is key. The mechanics of collecting classification-grade advanced EMI cued data with these systems have been shown to be fairly routine in the research community. As part of the ESTCP Munitions Response Live Site Demonstrations, industrial partners have been exposed to the MP system and the associated data collection and processing procedures.
In the past, analysis of data from these systems has been somewhat of a specialty, requiring specific software and knowledge to proficiently conduct. The successful transition of the processing and analysis procedures for MP data to the Geosoft Oasis montaj environment provides a clear path forward.