Special Issue on geophysics applied to detection and discrimination of unexploded ordnance

Unexploded ordnance (UXO) presents serious problems in Europe, Asia, as well as in the United States. Explosives and mines from World War I and World War II still turn up at European and Asian construction sites, backyard gardens, beaches, wildlife preserves and former military training grounds. The high rate of failure among munitions from 60-90 years ago is cited as one of the main reasons for such a high level of contamination. Apart from war activities, military training has resulted in many uncovered ordnance. It is especially true in the United States, where most UXO has resulted from decades of military training, exercises, and testing of weapons systems. Such UXO contamination prevents civilian land use, threatens public safety, and causes significant environmental concern. In light of this problem, there has been considerable interest shown by federal, state, and local authorities in UXO remediation at former U.S. Department of Defense sites. The ultimate goal of UXO remediation is to permit safe public use of contaminated lands. A Defense Science Board Task Force Report from 1998 lists some 1,500 sites, comprising approximately 15 million acres, that potentially contain UXO. The UXO-related activity for these sites consists of identifying the subareas that actually contain UXO, and then locating and removing the UXO, or fencing the hazardous areas off from the public. The criteria for clearance depend on the intended land end-use and residual hazard risk that is deemed acceptable. Success in detecting UXO depends on the ordnance's size, metal content, and depth of burial, as well as on the ability of geophysical systems to detect ordnance in the presence of metallic fragments from exploded UXO and other metal clutter

Demonstration Report: ESTCP UXO Discrimination Study ESTCP PROJECT # MM-0838

In 2003, the Defense Science Board observed: 'The problem is that instruments that can detect the buried UXOs also detect numerous scrap metal objects and other artifacts, which leads to an enormous amount of expensive digging. Typically 100 holes may be dug before a real UXO is unearthed! The Task Force assessment is that much of this wasteful digging can be eliminated by the use of more advanced technology instruments that exploit modern digital processing and advanced multi-mode sensors to achieve an improved level of discrimination of scrap from UXOs.' Significant progress has been made in discrimination technology. To date, testing of these approaches has been primarily limited to test sites with only limited application at live sites. Acceptance of discrimination technologies requires demonstration of system capabilities at real UXO sites under real world conditions. Any attempt to declare detected anomalies to be harmless and requiring no further investigation will require demonstration to regulators of not only individual technologies, but of an entire decision making process. This characterization study was be the second phase in what is expected to be a continuing effort that will span several years. The FY06 Defense Appropriation contained funding for the 'Development of Advanced, Sophisticated, Discrimination Technologies for UXO Cleanup' in the Environmental Security Technology Certification Program (ESTCP). ESTCP responded by conducting a UXO Discrimination Study at the former Camp Sibert, AL. The results of this first demonstration were very encouraging. Although conditions were favorable at this site, a single target of interest (4.2-in mortar) and benign topography and geology, all of the classification approaches demonstrated were able to correctly identify a sizable fraction of the anomalies as arising from non-hazardous items that could be safely left in the ground. To build upon the success of the first phase of this study, ESTCP sponsored a second study in 2009 at the former Camp San Luis Obispo, CA, a site with more challenging topography and a wider mix of targets-of-interest (TOI). There were two primary objectives of this study: (1) Test and validate detection and discrimination capabilities of currently available and emerging technologies on real sites under operational conditions; and (2) Investigate in cooperation with regulators and program managers how discrimination technologies can be implemented in cleanup operations

Modeling the resolution of inexpensive, novel non-seismic geophysical monitoring tools to monitor CO2 injection into coal beds

A sensitivity study of gravity and electromagnetic (EM) techniques, and amplitude vs. angle (AVA) analysis for CO{sub 2} movement in coal beds was based on the SECARB pilot test planned in the Black Warrior basin in Alabama. In the area of interest, coalbed methane is produced mainly from the Black Creek, Mary Lee, and Pratt coal zones at depths between 400 and 700 m and approximately 3 m thick on average. The permeability of coal in the Black Warrior basin decreases exponentially with depth as overburden stress increases. The permeability of the top layer is 100 mD, while the permeability of the deepest layer is around 1 mD. The pilot field test will include injecting a total of 1000 tons of CO{sub 2} into these three coal zones ({approx}300 tons to each zone). The density, sonic and resistivity well-logs from a deep disposal well a couple of miles from the pilot test site were used to create background (pre-injection) models. Our laboratory measurements of seismic velocity and electrical resistivity as a function of CO{sub 2} saturation on coal core samples were used to provide a link between the coalbed CO{sub 2} flow simulation models and the geophysical models. The sensitivity studies showed that while the response to the 300 tons of CO{sub 2} injected into a single layer wouldn't produce measurable surface response for either gravity or EM, the response due to an industrial-size injection would produce measurable surface signal for both techniques. Gravity inversion results illustrated that, provided we can collect high-quality gravity data in the field and we have some a priori information about the depth of the reservoir, we can recover the spatial location of CO{sub 2} plume correctly, although with the smoothing constraint of the inversion, the area was slightly overestimated, resulting in an underestimated value of density change. AVA analysis showed that by inverting seismic and EM data jointly, much better estimates of CO{sub 2} saturation can be obtained, especially in the third injection zone, where seismic AVA data fail to detect the high CO{sub 2} saturation. Analysis of spatial resolution and detectability limits show that gravity and EM measurements could, under certain circumstances, be used as a lower-cost alternative to seismic measurements

West Coast Regional Carbon Sequestration Partnership - Report on Geophysical Techniques for Monitoring CO2 Movement During Sequestration

The relative merits of the seismic, gravity, and electromagnetic (EM) geophysical techniques are examined as monitoring tools for geologic sequestration of CO{sub 2}. This work does not represent an exhaustive study, but rather demonstrates the capabilities of a number of geophysical techniques on two synthetic modeling scenarios. The first scenario represents combined CO{sub 2} enhance oil recovery (EOR) and sequestration in a producing oil field, the Schrader Bluff field on the north slope of Alaska, USA. EOR/sequestration projects in general and Schrader Bluff in particular represent relatively thin injection intervals with multiple fluid components (oil, hydrocarbon gas, brine, and CO{sub 2}). This model represents the most difficult end member of a complex spectrum of possible sequestration scenarios. The time-lapse performance of seismic, gravity, and EM techniques are considered for the Schrader Bluff model. The second scenario is a gas field that in general resembles conditions of Rio Vista reservoir in the Sacramento Basin of California. Surface gravity, and seismic measurements are considered for this model

A Feasibility Study of Non-Seismic Geophysical Methods for Monitoring Geologic CO2 Sequestration

Because of their wide application within the petroleumindustry it is natural to consider geophysical techniques for monitoringof CO2 movement within hydrocarbon reservoirs, whether the CO2 isintroduced for enhanced oil/gas recovery or for geologic sequestration.Among the available approaches to monitoring, seismic methods are by farthe most highly developed and applied. Due to cost considerations, lessexpensive techniques have recently been considered. In this article, therelative merits of gravity and electromagnetic (EM) methods as monitoringtools for geological CO2 sequestration are examined for two syntheticmodeling scenarios. The first scenario represents combined CO2 enhancedoil recovery (EOR) and sequestration in a producing oil field, theSchrader Bluff field on the north slope of Alaska, USA. The secondscenario is a simplified model of a brine formation at a depth of 1,900m

Geophysical Techniques for Monitoring CO2 Movement During Sequestration

The relative merits of the seismic, gravity, and electromagnetic (EM) geophysical techniques are examined as monitoring tools for geologic sequestration of carbon dioxide (CO{sub 2}). This work does not represent an exhaustive study, but rather demonstrates the capabilities of a number of geophysical techniques for two synthetic modeling scenarios. The first scenario represents combined CO{sub 2} enhanced oil recovery (EOR) and sequestration in a producing oil field, the Schrader Bluff field on the north slope of Alaska, USA. EOR/sequestration projects in general and Schrader Bluff in particular represent relatively thin injection intervals with multiple fluid components (oil, hydrocarbon gas, brine, and CO{sub 2}). This model represents the most difficult end member of a complex spectrum of possible sequestration scenarios. The time-lapse performance of seismic, gravity, and EM techniques are considered for the Schrader Bluff model. The second scenario is a gas field that in general resembles conditions of Rio Vista reservoir in the Sacramento Basin of California. Surface gravity, and seismic measurements are considered for this model

Advanced 3D Geophysical Imaging Technologies for Geothermal Resource Characterization

We describe the ongoing development of joint geophysical imaging methodologies for geothermal site characterization and demonstrate their potential in two regions: Krafla volcano and associated geothermal fields in Northeastern Iceland, and Coso Hot Springs in California, USA. The Coso field is a high temperature reservoir similar to Krafla in Iceland. Each area is a locus of significant geothermal energy production. The complex geology of these sites also makes them excellent targets for developing and testing of strategies for joint imaging of magnetotelluric (MT) and micro-earthquake (MEQ) data. Our ultimate aim is to construct coupled 3D resistivity and velocity models of these geothermal systems and use them to better understand and exploit them.Lawrence Berkeley National Laboratory (Subcontract 6927716

UXO detection and identification based on intrinsic target polarizabilities: A case history

Electromagnetic induction data parameterized in time dependent object intrinsic polarizabilities allow discrimination of unexploded ordnance (UXO) from false targets (scrap metal). Data from a cart-mounted system designed for discrimination of UXO with 20 mm to 155 mm diameters are used. Discrimination of UXO from irregular scrap metal is based on the principal dipole polarizabilities of a target. A near-intact UXO displays a single major polarizability coincident with the long axis of the object and two equal smaller transverse polarizabilities, whereas metal scraps have distinct polarizability signatures that rarely mimic those of elongated symmetric bodies. Based on a training data set of known targets, object identification was made by estimating the probability that an object is a single UXO. Our test survey took place on a military base where both 4.2-inch mortar shells and scrap metal were present. The results show that we detected and discriminated correctly all 4.2-inch mortars, and in that process we added 7%, and 17%, respectively, of dry holes (digging scrap) to the total number of excavations in two different survey modes. We also demonstrated a mode of operation that might be more cost effective than the current practice

Berkeley UXO Discriminator (BUD)

The Berkeley UXO Discriminator (BUD) is an optimally designed active electromagnetic system that not only detects but also characterizes UXO. The system incorporates three orthogonal transmitters and eight pairs of differenced receivers. it has two modes of operation: (1) search mode, in which BUD moves along a profile and exclusively detects targets in its vicinity, providing target depth and horizontal location, and (2) discrimination mode, in which BUD, stationary above a target, from a single position, determines three discriminating polarizability responses together with the object location and orientation. The performance of the system is governed by a target size-depth curve. Maximum detection depth is 1.5 m. While UXO objects have a single major polarizability coincident with the long axis of the object and two equal transverse polarizabilities, scrap metal has three different principal polarizabilities. The results clearly show that there are very clear distinctions between symmetric intact UXO and irregular scrap metal, and that BUD can resolve the intrinsic polarizabilities of the target. The field survey at the Yuma Proving Ground in Arizona showed excellent results within the predicted size-depth range