This project was conducted to demonstrate a fixed-wing platform for deploying low altitude remote sensing technologies that can be used to help meet the increasing demand on the Department of Defense (DoD) for low-cost, high-resolution wide area assessment (WAA) of former and active military facilities contaminated with unexploded ordnance (UXO). The objective of the demonstration of the Minimum Altitude Remote Sensing (MARS) system was to evaluate the ability of this platform and technology to characterize large sites cost efficiently, reliably, and safely. The MARS airborne UXO mapping system was developed, successfully tested, and deployed in Europe by SeaTerra GmbH in Germany. Sky Research, Inc. (SKY) demonstrated this system for application in the United States in partnership with SeaTerra.
The site selected for demonstration was the Former Kirtland Precision Bombing Range (KPBR) located near Albuquerque, New Mexico, in order to provide the ability to compare performance, results, and cost with another low altitude WAA technology, helicopter magnetometry (HeliMag). HeliMag was previously demonstrated at the site as part of the ESTCP WAA Pilot Program. In addition, the results of this demonstration were integrated into the SKY WAA Geographic Information System (GIS) with the WAA data collected at the site (HeliMag, Light Detection and Ranging [LiDAR], orthophotography, and ground-based digital geophysical mapping [DGM] data) to facilitate data analysis, historical information integration, and data access.
The objective of this project was to demonstrate and certify a fixed-wing platform for low-cost, high-resolution WAA of former and active military facilities contaminated with UXO. The objectives of this demonstration were to test and evaluate the MARS system in the United States and compare the performance, results, and cost to HeliMag technology.
SKY acquired the CT Short Wing (SW) model light sport aircraft (LSA) for this demonstration. This model lightweight aircraft, a slightly different model than the one used by SeaTerra in Europe, did not affect the deployment of the technology. The aircraft has a 8.9 m wingspan, a length of 6.2 m, and can fly at a minimum height above ground of 2 m. It uses modern German glider structural design techniques and is essentially all-composite glass fiber reinforced plastic with very little ferrous metal and a low signature footprint. An array of six Geometrics Model 822A cesium vapor magnetometer sensors was mounted on a sensor boom attached to the aircraft wings. The sensors were deployed at separations between 1.15 and 2.0 m. SeaTerra’s AGS MK3 frequency counter and data acquisition system (DAS) were used to record data at between 140 to 160 Hertz (Hz) with approximately a 0.2 nanotesla (nT) noise floor on the outer sensors and 0.5-0.7 nT noise floor on the inner sensors (after processing).
Daily flight durations were planned to be approximately 6 hours per day (assuming an 8-hour daily window for flying). Because of unfavorable weather conditions (frequent high winds and rain or thunderstorms), density altitude, and thermal effects that were encountered, it was not possible to safely operate the CT as many hours per day as planned. Daily flight durations ranged from 1.4 hours to a maximum of 5.2 hours, with an average of 3.5 hours for days when conditions for flying were favorable. There were 3 days that no flights were conducted due to rain and/or high winds. During the survey, data were collected over 2,856 acres.
A number of 105-mm high-explosive anti-tank (HEAT) 105-mm and 155-mm projectiles were blind-seeded in an area south of the Double Eagle Airport. For manually selected target picks, there were 2.1 anomalies per acre, and detection probabilities were 11, 60, and 93% for the 105-mm HEAT, 105-mm projectile, and 155-mm projectile, respectively. Using an automatic detection algorithm and a threshold of 5 nT, anticipated detection probabilities were 62, 71 and 100% for the above three items with 19 alarms per acre.
A HeliMag survey was flown over the survey area in 2005, and portions of the site were also covered by a towed-array survey. When target picking using the total-gradient data, the MARS system experienced an inflection point at around 4 nT/m (where the number of alarms increases markedly), compared to 3 nT/m for the HeliMag data.
The demonstrators compared the MARS and HeliMag anomaly density maps in two regions of the northern part of the site (Areas 1 and 2). In Area 1, the MARS and HeliMag derived densities were comparable, and both predicted a target of approximately the same size, shape, and concentration. In Area 2, the density estimates were considerably different with the MARS densities—on average, 3.5 times lower than the HeliMag. This difference was largely attributed to the approximately 1.0 m higher elevation of the MARS sensors compared to the HeliMag. The differences were particularly marked around a fence that cut across a high concentration target region. The CT aircraft had to fly higher over the obstacle and took longer to return to its normal survey altitude than the helicopter.
Using the towed-array data as groundtruth, the HeliMag system exhibited detection probabilities (Pd) of Pd=0.9 on Areas 1 and 2 at five false-alarms per acre. In contrast, for Area 1 the MARS Pd=0.7 at five alarms per acre and rose slowly to Pd=0.85 at 30 alarms per acre. MARS detection performance was significantly worse for Area 2, with Pd=0.6 at around five false alarms per acre, rising to Pd=0.8 at 20 false alarms per acre.
The pilots were able to consistently fly the aircraft at the target 2 to 3 m above ground level. However, the poor detection performance in Area 2, especially in the area where the pilot had to avoid a fence, indicates that surface tracking is more problematic for the CT than a helicopter.
This project has shown that MARS performance is generally inferior to HeliMag but that the costs are between 51 to 66% of a HeliMag survey. In the flat, open areas of Kirtland, MARS survey altitudes and detection performance were comparable to that of HeliMag. Therefore, in those types of areas, MARS could substitute for HeliMag and potentially reduce survey costs. In areas with more topographic complexity, MARS survey altitudes and performance were significantly worse than that of HeliMag, and MARS was not an adequate substitute.
The niche for MARS appears to be in flat, open sites with larger (105 mm or greater) caliber munitions, particularly when those sites are relatively small because then a MARS survey is a much cheaper alternative than HeliMag.