Geophysical technologies for supporting munitions waste remediation have focused on the problems of detecting, locating, and mapping the presence of underground objects. Experience has shown that most underground objects detected by these systems present no safety hazard or need to be excavated. If reliable means of distinguishing hazardous from nonhazardous objects could be developed, significant resources for munitions remediation programs could be saved and more effectively deployed to mitigate safety hazards.
Other researchers have shown a likelihood of being able to characterize buried targets via sophisticated inversion algorithms. These algorithms require high-fidelity sensor systems combined with high-fidelity positioning systems. Existing sensor technologies provide good quality sensor data, but practical high-resolution positioning systems (on the order of 1 cm error) remain a challenge.
ENSCO, Inc. conducted a demonstration at Aberdeen Proving Grounds (APG) on September 12-13, 2006, of the second generation small area inertial navigation tracking system (SAINT) technology integrated with an EM61-HH metal detector.
This demonstration highlighted the integration of SAINT with a standard EM61-HH metal detector. The primary objective was to verify the three-dimensional (3-D) positioning accuracy of the EM61-HH sensor provided by SAINT. Because no communication is needed with auxiliary components or satellites, normal operation is not affected by heavy vegetation, elevation change, water, or tree cover, as is the case for most other positioning systems. During post-processing, the EM61-HH data was merged with the SAINT position data; however, the overall performance of the EM61-HH was not assessed. The focus was on the position accuracy.
The demonstration was conducted in the calibration grid at APG and included the interrogation of 23 targets in the calibration grid. Post-processing provided EM61-HH data merged with 3-D position data for the 23 targets in the calibration grid with all positions referenced in the Universal Transverse Mercator (UTM) coordinates.
Success was defined as demonstrating relative position errors of the sensor coil of less than 2 cm at 1 standard deviation along each of the three axes of the local positioning reference frame. Secondary demonstration objectives were to show robustness and reliability of the system, ease of use, and simplicity of post-processing. Both objectives were met.
SAINT was demonstrated to produce relative positioning accuracy of less than 5 mm and inversion fit quality consistent with a <1 cm positional accuracy. This accuracy is expected to be sufficient to allow target characterization based on the EM61-HH sensor data tied to accurate relative geolocation. During the demonstration, data were collected at a rate of six targets per hour for a single operator. In production use, a minimum rate of 12 targets per hour is anticipated. This production rate is expected to result in an interrogation cost of $7 per target, thus potentially saving a substantial percentage of munitions remediation costs.
This demonstration documented the relative positioning accuracy and land-area survey rate of the inertial navigation technology. Logistical issues (which are critical to munitions operations) were demonstrated by documenting activities required to complete the demonstration. Cost of the technology was estimated and compared to existing technology. Thus, the outcome of this demonstration provides end users with an understanding of the technical, logistical, and financial impact of this technology, allowing them informed decision making.