Hollis H. Bennett

Overview of multimethod geophysical system development for enhanced near-surface target detection, discrimination, and characterization

Near-surface geophysical “targets” include unexploded ordnance (UXO), landmines, cavities (including tunnels and underground facilities), contaminant plumes, utilities (including underground storage tanks, pipelines, etc.), archaeological artifacts, graves, forensic evidence, structural foundation investigations for new and existing structures, and assessing the condition of engineered structures (e.g., bridges, dams, levees, roads, airfields, buildings). Application of near-surface geophysics to detect and characterize any of these “targets” is in the public interest, and many applications are clearly and directly related to public safety. While the detection of these targets in a geologic background can often be challenging, the discrimination of the desired target signatures or expressions from “false alarm” target signatures can be an even greater challenge. The discrimination challenge can be as simple as a “go/no-go” decision on the target, or the properties of the target may need to be further characterized after the decision. There is near unanimity among geophysicists (a rare thing) that multimethod, collocated complementary geophysical data enhance not only target detection but also the capability for discrimination and characterization. The U.S. Army Engineer Research and Development Center (ERDC) conducted a multiyear research and development effort that resulted in complementary, collocated simultaneous geophysical survey capabilities for near-surface targets.

Evaluation of Seismic-Acoustic Analysis Methods for a Real-time UXO Monitoring System

The Department of Defense (DoD) uses over two million rounds of high-explosive (HE) munitions per year (Defense Science Board Task Force, 2003). A small percentage does not explode, thus generating unexploded ordnance (UXO) in current range areas at a substantial rate. As these ranges are closed, the DoD becomes responsible for the environmental restoration of the affected properties. Current methods of UXO remediation are costly because of high false alarm rates. Our current research is to develop a complementary technology that will alleviate false alarm rate by detecting, classifying, and locating UXO in near real time (less than 1 minute) as a munition impacts the range. This technology will utilize an array of buried seismic sensors in a calibrated range area, along with a set of algorithms based on theoretical and applied seismology and statistical analysis. Initial field tests at three sites focused on developing concepts of the seismic and acoustic location of ordnance impacts. Our research program developed from these initial field tests has four primary objectives: 1) fully implement a wired seismic-acoustic ordnance impact location system for live fire ranges; 2) develop a system capability to discriminate high-order (HE), loworder (partially exploded), and zero-order (UXO) events; 3) reduce location error to a stringent program metric of 1–2 m; and 4) investigate the feasibility of developing a wireless implementation of the technology. This paper describes the procedures and results from follow-on tests that were conducted in two locations at the U.S. Army Aberdeen Proving Ground (APG), Maryland. These tests were used to evaluate potential seismic-acoustic methods and system configurations for a Seismic-Acoustic Impact Monitoring Assessment (SAIMA) system for mitigating UXO hazards. Significant results from this work include: 1) seismic impulses from low-order impacts were detected at distances up to 1,000 meters; 2) classification features based on measurements of the amplitude of acoustic and seismic phases produce clear discrimination between HE and UXO impacts; 3) calculated location solutions for HE and UXO impacts yield an average location error of 10–20 meters; and 4) empirical observation and waveform modeling demonstrated that surface waves dominate the signal at all distances and therefore should be the primary phase used for all components of analysis. Furthermore, these tests demonstrated the current system design, allowing further enhancements, is capable of meeting the initial research objectives (1) and (2). Future research will focus on improving system performance with refinement of the sensor-layout geometry and the detection and location algorithms through system error analyses and follow-on field testing.

Review of Magnetic Modeling for UXO and Applications to Small Items and Close Distances

Abstract Prior to 1990, UXO were generally modeled or approximated as compact, ferrous objects; the model was effectively a uniformly magnetized sphere of iron at a specified or an unknown distance from the magnetic sensor. Correlations were developed between various UXO, represented as compact masses of iron, and magnetic anomaly signature features such as maximum positive value, peak-to-peak value, and wavelength. The uniformly magnetized sphere, equivalent to a point dipole model external to the sphere, cannot account for magnetic phenomenology of actual UXO, which exist in forms ranging from approximately spherical to highly elongated, with elongations as large as 5 (ratio of length to diameter). UXO are generally ferrous, with large magnetic permeability, although some can contain aluminum or other non-magnetic metals. This paper reviews the phenomenology of models applied to simulation of UXO magnetic anomalies. The multipole expansion solution of the prolate spheroid model in earths magnetic field...

EMPLOYING MULTIPLE GEOPHYSICAL SENSOR SYSTEMS TO ENHANCE BURIED UXO "TARGET RECOGNITION" CAPABILITY

Abstract : Millions of acres of former and currently used military training and testing ranges are potentially contaminated by surface and buried unexploded ordnance (UXO), giving rise to requirements for UXO environmental restoration of formerly used sites and for sustainable use and active range cleanup. Geophysical surveys are required to map the location of buried UXO. The major cost driver of current cleanup and restoration is the inability to discriminate between buried false alarm and UXO targets. Excavation of false alarm targets is the major cost driver of UXO cleanup. Application of complementary geophysical sensor systems increases the potential for discrimination of UXO targets from false alarm targets. Development of new and innovative data integration methods and cooperative geophysical inversion algorithms allows enhanced discrimination and gives potential for target classification.

Signature mining and analysis of urban environment data

When investigating low energy acoustic signatures such as infrasound, determining signal from noise can be complex, particularly in urban environments. Understanding the characteristics of all sources will assist in suppression of signatures deemed to be noise, and in the enhancement of the signatures of items of interest. The first part of the task is to determine the signatures of interest. These signatures will form the basis set for different classifiers. Development of classifiers for these signals of interest will involve categories such as stationary signals, transient signals, and types of infrastructure including utilities. Following classification, an idea of the usage can be determined based on signals from the infrastructure detected. The research to be presented focuses on signal extraction from a data set in order to begin development of classifiers and eventual detection algorithms for infrasound signals in urban environments.

Initial Development of a High-frequency EMI Sensor for Detection of Subsurface Intermediate Electrically Conductive (IEC) Targets

The U.S. military has developed and currently uses composite material munitions. These composite munitions are typically comprised of carbon fiber and, because of their low electrical conductivity, have a much lower electromagnetic induction signature, which makes them difficult to detect using traditional metal detecting methods. The term intermediate electrically conductive (IEC) is used to describe these lower conductivity materials, with conductivity, σ , typically in the range 10 σ 5 S/m. The electromagnetic induction (EMI) relaxation response of carbon fiber munitions peaks in the low megaHertz range (

Evaluation and Current Results of the Seismic Acoustic Impact Monitoring Assessment (SAIMA) System

For the past several years, Quantum Technology Sciences (QTSI) and U.S. Army Engineering Research and Development Center (ERDC) have been developing a system to actively sustain present and future artillery ranges at zero unexploded ordnance (UXO) gains. With the Department of Defense (DoD) using over two million high-explosive (HE) munitions per year with a significant fraction as UXO, reducing costly range remediation and environmental restoration efforts will offer significant savings. The developed Seismic Acoustic Impact Monitoring Assessment (SAIMA) system is not designed for past ranges, but as a complementary technology to detect, locate within two meters, and classify UXO in near realtime to aid existing cleanup technologies. Feasibility and descriptions of system components have been previously provided (VanDeMark et al., 2009, 2010, 2013). The current system is composed of multiple buried seismic arrays encircling a mortar or artillery impact area, communications from the arrays to a central processing station, and a processing unit that employs an algorithm suite based in the seismology and statistical analysis disciplines to detect, locate, and classify the HE or UXO impact. Recent deployments of the SAIMA system have demonstrated hardware maturity and algorithm refinements to nearly enable the goal of locations within two meters. A field deployment at Ft. Sill, Oklahoma, in June 2012 demonstrated acoustic locations at a large range (QTSI, 2012). Subsequent systems tests with five arrays using a synthetic UXO source (kinetic source only; no acoustic phases) on a small field (80 m by 80 m) resolved locations within 0.5 m of ground truth with coverage ellipses at 0.1 m 2 (time and azimuth). On a small mortar field,

Portable Magnetic/Frequency Domain Electromagnetic Induction Sensor System Development

An unexploded ordnance (UXO) survey instrument that simultaneously collects total field magnetic data and frequency domain electromagnetic (FDEM) induction data was developed and tested for the detection and characterization of buried UXO. The system is comprised of an FDEM sensor operating at 9.8 kHz and a cesium vapor magnetometer. The system was initially tested in dynamic survey (detection) and static cued survey (characterization) modes at the Naval Research Laboratory Blossom Point UXO test facility in Maryland. During these tests, electromagnetic (EM) induced bias in the magnetic data was mitigated by physically offsetting the magnetometer from the EM transmitter coils. In the dynamic survey, the aggregate performance exceeded the detection rates for the individual component sensor technologies. The cued analysis tests showed that target features can be determined by using model-based analyses, and the location estimate errors provided by these analyses were consistently better than the dynamic survey results.

Rapid Wide Area Assessment for Large Surface Munitions Via an Infrared Surveillance System

The purpose of this study is to determine the feasibility of using a commercially available thermal infra-red surveillance system for detecting large surface munitions as part of an UXO Wide Area Assessment. The work was performed in partnership with multiple US Army Corps of Engineers agencies and the Isleta Pueblo. The area of interest is located on the Isleta Pueblo. The US Army Engineer Research and Development Center team flew a low cost airborne surveillance system (Ultra 8500 FW) on a single engine fixed-wing aircraft over the area of interest. The airborne missions were scheduled to maximize the thermal separation between the UXO and the natural surroundings based on diurnal data collections. The flight profiles were collected at approximately 700 feet above ground level at an approximate ground speed of 100 knots in both contour following and parallel transects depending on the terrain. The thermal signatures were recorded on digital media and frames containing potential UXO (both targets and false alarms) will be selected for field verification by Shaw Environmental, Inc. Examples of the data collected, advantages and disadvantages of utilizing the thermal airborne system, video format and compression artifacts, and field verifications will be shown.

Laser polarization and reflectance characterization of selected target and background material

This paper describes the relative polarization and reflectance characterization of background and selected target items to demonstrate the differences material type and source wavelength have on these measurements. The advanced reflectance and polarization instrument (ARPI) was modified to allow three lasers with different wavelengths to be used. This allowed for similar spot size, location, and angles to be used to collect the measurements. ARPI was used to collect polarized and cross-polarized returns from the polarized laser source at an incident angle of 0, 5, 10, and 20 degrees. These measurements were used to calculate the relative percent polarization and percent reflectance. Analysis of the measured relative polarization and reflectance consists of single wavelength and multiwavelength comparisons with man-made and background items. A direct comparison is made between natural and man-made materials and different wavelengths of light. This careful comparison of differences between wavelengths will demonstrate which of the wavelengths produces the best and most consistent separation between background and manmade items. Our preliminary analysis shows that most man-made items give different polarization and reflectance returns than background items. Also, the analysis shows nominal variability between the three different wavelengths for background items and man-made items.