Empirical Evaluation of Advanced Electromagnetic Induction Systems - Deployment Factors Affecting Efficiency of Implementation
Tamir Klaff | CH2M HILL
Objectives of the Demonstration
In 2013 and 2015, CH2M HILL, Inc. (CH2M) performed two Environmental Security Technology Certification Program (ESTCP) Munitions Response Live Site Demonstrations as part of project MR-201314. The 2013 demonstration was performed at the Shooting Fields (MU705), located at New Boston Air Force Station (NBAFS), New Hampshire. The 2015 demonstration was performed at Munitions Response Site (MRS) R‑04A West, at Tobyhanna Army Depot (TOAR) Formerly Used Defense Site, in Pennsylvania.
CH2M performed the demonstrations at NBAFS and TOAR using the Naval Research Laboratory (NRL) Time-domain Electromagnetic Towed Array Detection System 2x2 (TEMTADS), an advanced transient electromagnetic system designed for the detection and classification of munitions and explosives of concern. Additional data was collected at each of these sites by Black Tusk Geophysics using the Man Portable Vector (MPV).
The demonstration at NBAFS was designed to investigate the classification methodology at a site suspected to contain a high density of subsurface metallic objects, as well as a variety of munitions such as 20-millimeter (mm) projectiles. The TEMTADS was employed in both dynamic and cued modes using the sensor’s standard wheel configuration. Positioning was achieved through the use of a real time kinematic (RTK) global positioning system (GPS).
CH2M’s demonstrations at NBAFS and TOAR were designed to investigate the use and document the capabilities of the TEMTADS advanced electromagnetic induction (EMI) sensor at sites with challenging conditions through dynamic and cued data collection. Analysis of the data was performed using conventional and advanced geophysical classification -specific data processing methods.
Approximately 6.1 acres were mapped with the TEMTADS system in dynamic mode. The density of geophysical anomalies identified from the survey was an order of magnitude higher than anticipated. In order to stay within the budgeted scope of the demonstration, 1,500 anomalies from a subarea of the site were selected for cued interrogation with the same system. Data analysis of the cued measurements confirmed a high density of metal with a large percentage of the anomaly locations being multi-target scenarios. The project team was halted after a several week review of intrusive results, which determined that classification at the site would 1) not result in cost savings as opposed to intrusively investigating all anomalies and 2) be ineffective. This decision was based on the fact that 70 percent of the intrusive investigations resulted in discovery of a target of interest (TOI) and each dig typically yielded multiple items. Approximately 33 percent of the anomalies investigated resulted in three or more sources and, under these circumstances, the inversion results do not appear to accurately represent the ground truth.
The demonstration at TOAR was designed to investigate the use of advanced EMI sensors at a densely wooded site with challenging micro-terrain features for detecting munitions down to the size of 37‑mm projectiles. The TEMTADS was employed in both dynamic and cued modes in two-person litter mode and positioning was achieved through the use of a Robotic Total Station (RTS).
Approximately 0.71 acre was mapped with the TEMTADS system. Production was significantly hindered by the remote location and site conditions and coverage for only one of the four grids initially selected for investigation was at 100 percent. Because of the challenging conditions at TOAR, production rates achieved as part of the demonstration are estimated to be much lower than production rates at sites with more favorable conditions.
A total of 429 anomalies were identified by the TEMTADS dynamic data analysis. These anomaly locations, and an additional 68 targets selected from the MPV dynamic data, were interrogated with the TEMTADS system. The cued data were used to classify each target as being a TOI or high-likelihood non-TOI. The TEMTADS data collection and analysis resulted in successful detection and classification of all known TOIs.
The estimated cost of deploying the TEMTADS based on the demonstrations at NBAFS and TOAR is high, approximately two or three times the cost of deploying commercially available systems such as the Geonics EM61-MK2. The primary demonstrated advantage of deploying the TEMTADS lies with the ability to use the data collected to classify targets and thus to produce a prioritized dig list. At TOAR, the use of a prioritized dig list would have reduced the number of digs by 71 percent or more. This would result in an overall cost savings of approximately 30 percent in the cost of the intrusive investigation. For sites such as TOAR, where targets are successfully discriminated, the higher cost associated with deployment of the TEMTADS is justified on the basis that it can substantially reduce the cost of digging. For sites such as NBAFS, where the anomaly density is very high and detecting munitions down to the size of 20‑mm projectiles is required, use of the TEMTADS is not warranted.
While the RTS can be used for positioning in open areas or narrow corridors, the TEMTADS unit cannot be carried in such a way that it is always moving perpendicular to the RTS base station, and thus avoid being shielded from the base by the operators. In order to facilitate positioning in a heavily wooded area using RTS, the RTS prism located above the TEMTADS unit had to be raised above the heads of the operators. This allowed free movement by the operators and increased the data production rate; however, the added height of the prism more than likely caused dynamic Instrument Verification Strip measurement quality objective (MQO) failures because of the oscillation of the prism while walking. Additionally, dynamic data with a lower prism height were not collected, so it is not possible to rule out that just walking in litter mode with the RTS was not the issue. Prior experience using the RTS with the TEMTADS in wheeled mode had no positioning MQO failures.
Points of Contact
Mr. Tamir Klaff
SERDP and ESTCP