Statistical analysis of metallic anomaly patterns at former air force bombing ranges

This paper summarizes the findings of a statistical analysis of the locations of metallic anomalies detected at the Pueblo Precision Bombing Range Number 2 in Otero County, Colorado, and at the Victorville Precision Bombing Range in San Bernardino County, California. The purpose of the study is to explore whether statistical properties of the pattern of anomaly locations can be used to discriminate areas likely to contain unexploded ordnance (UXO) left over from previous bombing practice from those unlikely to contain UXO. Techniques for discriminating areas with and without UXO are needed because historic records have left an incomplete account of previous military training activities, so that locations historically used for target practice are often unknown. This study differs from previous research on metallic anomaly data at former military training ranges in that it analyzes the spatial pattern of the discrete locations of the anomalies, rather than the average number of anomalies per unit area. The results indicate that differences in spatial pattern may be a distinguishing feature between areas that were used for target practice and those that are unlikely to contain UXO, even when a large number of ferrous rocks and other inert metallic anomalies are present. We found that at both of the former bombing ranges, the anomaly patterns in sample areas that are distant from all known bombing targets are consistent with a complete spatial randomness pattern, while those near the target areas fit a radially symmetric, bivariate Gaussian pattern. Furthermore, anomaly location patterns generated by surveys with airborne metal detectors have the same statistical properties as the patterns generated by surveys with on-ground detectors, even though the airborne systems detect only a subset of the anomalies found by the ground-based detectors. Thus, pattern information revealed by airborne surveys with metal detectors may be useful in identifying areas where careful searches for UXO are needed.

Intelligent data fusion for wide-area assessment of UXO contamination

The remediation of sites contaminated with unexploded ordnance (UXO) remains an area of intense focus for the Department of Defense. Under the sponsorship of SERDP, data fusion techniques are being developed for use in enhancing wide-area assessment UXO remediation efforts and a data fusion framework is being created to provide a cohesive data management and decision-making utility to allow for more efficient expenditure of time, labor and resources. An important first step in this work is the development of feature extraction utilities and feature probability density maps for eventual input to data fusion algorithms, making data fusion of estimates of data quality, UXO-related features, non-UXO backgrounds, and correlations among independent data streams possible. Utilizing data acquired during ESTCP’s Wide-Area Assessment Pilot Program, the results presented here successfully demonstrate the feasibility of automated feature extraction from light detection and ranging, orthophotography, and helicopter magnetometry wide-area assessment survey data acquired at the Pueblo Precision Bombing Range #2. These data were imported and registered to a common survey map grid and UXO-related features were extracted and utilized to construct survey site-wide probability density maps that are well-suited for input to higher level data fusion algorithms. Preliminary combination of feature maps from the various data sources yielded maps for the Pueblo site that offered a more accurate UXO assessment than any one data source alone.

Independent component analysis for UXO detection in highly cluttered environments

Statistical signal processing techniques have shown progress in discriminating UXO from clutter when the objects occur in isolation. Under this condition, only a single object contributes to the measured sensor data. For multiple closely spaced subsurface objects, however, the unprocessed sensor measurement is a mixture of the responses from several objects. Consequently, the unprocessed measurements cannot be used directly to discriminate UXO from clutter. In this paper, we implement independent component analysis (ICA), a well-established blind source separation (BSS) technique, to recover the unobserved object signatures from the mixed measurement data obtained by simulating electromagnetic induction (EMI) sensor data, and then use the recovered signatures for UXO/clutter discrimination. Discrimination performance depends on multiple factors, including the number of clutter objects in proximity to the UXO, the separation distance between the UXO and clutter, and the number of mixed measurements available. Simulation results are presented illustrating the impact of these factors on discrimination performance.     

A Bayesian approach to monitoring and assessing unexploded ordnance remediation progress from munitions testing ranges

We present a statistical methodology which aims to monitor and assess the progress of unexploded ordnance remediation. We explicitly quantify the probability that each buried sensor-identified anomaly is not a target of interest conditional on the information gleaned from anomalies which have been dug and identified. We provide a measure of confidence that the anomalies which remain onsite after remediation are not unexploded ordnance—this measure of confidence is gleaned through Monte Carlo methods. The methodology is iterative in that, at any point in the remediation process, we can assess remediation progress and compute the probability that no targets of interest remain given the available dig information.     

Application of a library based method to time domain electromagnetic data for the identification of unexploded ordnance

A simple library based algorithm for the identification of unexploded ordnance is tested on time domain electromagnetic data. A library of polarization tensors is generated from data acquired on a test stand over a collection of different UXO. The objective of the algorithm is to determine which target of the library is most likely to have produced an observed data anomaly. For each target in our library a non-linear inverse problem is solved for the position and orientation that minimizes the least-squares difference between the observed data anomaly and the data predicted from each target. This technique avoids direct inversion for polarization tensor, making it feasible for cases where sensor data quality may not be sufficient to support confident estimation of model parameters. For cases where the background soil response is significant, we also invert for the t⁻¹ decay characteristic of viscous remnant magnetic soil. We present results of preliminary tests of the library technique to Geonics EM63 time domain electromagnetic data collected on a test plot seeded with UXO. These tests demonstrate an excellent ability to accurately identify isolated targets. Misidentification of single targets occur when data anomalies have low signal to noise ratios or when targets within the library have similar polarization tensors.     

Remanence correction in magnetic interpretation with the infinitely deep plate model

Summary Conditions are given under which two thick plates, differing in dip, apparent susceptibility, and remanence, will produce similar magnetic anomalies. From these conditions correction formulae are developed. Using these formulae the dip and susceptibility of a plate with remanent magnetization can be obtained from those of non-remanent plate. An interpretation procedure is suggested where the magnetic anomaly is first interpreted by means of a plate without remanence, dip and apparent susceptibility are then estimated by using the correction formulae developed. Thickness, position and depth of the plate are unaffected by the remanence correction procedure. The procedure is independent of the field component measured.     

A CONTROL OF TWO-DIMENSIONAL MAGNETIC INTERPRETATION BY THREE-DIMENSIONAL MODEL BODY ANOMALIES*

In magnetic routine interpretation the comparison of two-dimensional model curves with measured magnetic anomalies is widely used for an approximate evaluation of the position and depth of magnetic models. Before starting an interpretation of a survey by means of two-dimensional models, it is very useful to have an idea of the shape of anomalies caused by extended but finite bodies, taking into account various strike directions: Three sets of anomalies of thin plates (horizontal length 19, downward length 9, width 1) dipping 30°, 60°, and 90° resp. for various strike directions and an inclination of 20° were computed. Some of these anomalies, e.g. those with nearly N-S strike direction look rather complicated, and at the first glance one would not expect that they are caused by such simple bodies. Several profiles crossing the computed anomalies perpendicularly were interpreted two-dimensionally. For less extended anomalies the depths determined for the top of the plates are 10-20% too small, the magnetization amounts to 50–75 % of the value of the finite bodies. The interpretation of the profiles covering more extended anomalies gave very accurately the same values for the position, depth and magnetization for the two-dimensional body as for the original three-dimensional model. Anomalies of vertical prisms with varying extensions in the y-direction were computed. Their differences in amplitude and in the distance maximum-minimum show that interpretation of short anomalies by two-dimensional methods yields depth errors of up to 20 percent. To see the possibilities of the separation of superimposed anomalies dike anomalies were added to the anomaly of a broad body in great depth and several attempts were made to interpret parts of the composite anomalies. The interpreted bodies lie too deep. In complicated cases the depth values can have large errors, but experienced interpreters should be able to keep the errors in the range of one third of the depth values.     

Evaluation of spatially clustered ordnance when using compliance sampling surveys after clean-up at military training sites

After site clean-up teams have removed all of what they believe to be UXO within a specific impact area, statistical compliance sampling is a possible method for verifying with a specified probability that this area has been cleaned to specifications. Schilling [J Qual Technol 10(2):47–51, 1978, Acceptance sampling in quality control. Marcel Dekker, Inc., New York, 1982] developed a compliance sampling methodology based on the hypergeometric distribution. Bowen and Bennett (1987) also use compliance sampling where they provide an approximation for estimating the number of samples (n) required to state with desired probability that the entire population of sample units (N, where n < N) are in compliance with cleanup goals. This article describes two methods (anomaly and transect) for applying the Schilling [J Qual Technol 10(2):47–51, 1978, Acceptance sampling in quality control. Marcel Dekker, Inc., New York, 1982] compliance sampling method to military training sites. After describing these methods, a simulation study is presented which demonstrates the performance of transect compliance sampling calculations based on varied degrees of clustered UXO within a specific impact area and different types of sampling routines.     

磁异常揭示的峨眉山大火成岩省的深部结构

峨眉山大火成岩省位于中国西南部,在晚二叠纪约260 Ma喷发出巨量的大陆溢流型玄武岩.对于大火成岩省的岩浆喷发,在地下必定有一个相应的大规模岩浆聚集和运移系统.地球物理方法是探测岩石圈内部的有效方式.峨眉山大火成岩省为镁铁质岩浆喷发,由于镁铁质-超镁铁质岩石一般具有强磁性,因此,在喷发结束之后,地下岩浆系统如果被镁铁质岩浆填充,冷却固化成为岩石圈的一部分,很有可能会引起磁异常.本文使用区域磁异常数据来对峨眉山大火成岩省的深部构造进行研究.该区域的磁异常由一系列离散的异常组成,通过3D磁化率反演可以得到磁性体的空间分布.由于磁异常中具有明显的剩磁,直接使用经典的反演方法会有较大误差,我们首先将磁异常转换为弱敏感于磁化方向的磁异常模量,再使用模量数据进行3D反演,得到地下空间内磁异常源的分布.经过分析认为这些离散分布的磁异常源反映了岩石圈内部的镁铁质-超镁铁质侵入体.侵入体的位置可能反映了底侵和内侵的镁铁质岩浆固化形成的侵入体,代表镁铁质岩浆房位置或者岩浆运移的主要通道.     

UXO target area identification with hidden Markov models

Site characterization activities at potential unexploded ordnance (UXO) sites rely on sparse sampling collected as geophysical surveys along strip transects. From these samples, the locations of target areas, those regions on the site where the geophysical anomaly density is significantly above the background density, must be identified. A target area detection approach using a hidden Markov model (HMM) is developed here. HMM’s use stationary transition probabilities from one state to another for steps between adjacent locations as well as the probability of any particular observation occurring given each possible underlying state. The approach developed here identifies the transition probabilities directly from the conceptual site model (CSM) created as part of the UXO site characterization process. A series of simulations examine the ability of the HMM approach to simultaneously determine the target area locations within each transect and to estimate the unknown anomaly intensity within the identified target area. The HMM results are compared to those obtained using a simpler target detection approach that considers the background anomaly density to be defined by a Poisson distribution and each location to be independent of any adjacent location. Results show that the HMM approach is capable of accurately identifying the target locations with limited false positive identifications when both the background and target are intensities are known. The HMM approach is relatively robust to changes in the initial estimate of the target anomaly intensity and is capable of identifying target locations and the corresponding target anomaly intensity when this intensity is approximately 60% higher than the background intensity at intensities that are representative of actual field sites. Application to data collected from a wide area assessment field site show that the HMM approach identifies the area of the site with elevated anomaly intensity with few false positives. This field site application also shows that the HMM results are relatively robust to changes in the transect width.     

Interpretation of high-resolution low-altitude helicopter magnetometer surveys over sites contaminated with unexploded ordnance

Throughout the world, millions of acres of potentially productive land are contaminated with unexploded ordnance due to either past conflicts or to military training activities. Low-level helicopter magnetometry (HeliMag) is currently being used to rapidly survey large areas and identify regions that are potentially clear of hazardous munitions. One configuration currently in use comprises seven cesium vapor magnetometers, horizontally spaced 1.5 m apart and mounted on a boom several meters in front of a Bell 206L helicopter. Magnetometer data are collected at 400 Hz at altitudes as low as 1.5 m above the ground along transects spaced 7 meters apart. From this dense, high-resolution data, potential metallic targets as small as a 60 mm mortar are identified using manual and/or automatic target picking methods. The target picks are then used to estimate densities of potential contamination. 100% detection is generally not feasible, so that HeliMag is usually applied in a characterization rather than in a clearance mode. We describe a HeliMag survey collected over a UXO contaminated site at Yekau Lake, near Edmonton, Canada. The objective was to identify the location and extent of an 11.5 pound bomb target area at a former training range. The target density estimates derived from manual picks were strongly influenced by geology and clutter and did not reflect the underlying density of ordnance and ordnance related clutter. By fitting a dipole model to each target pick, and comparing it to the expected response of the target item, we could estimate the density of objects with similar size/shape to an 11.5 pound bomb. This analysis clearly identified an area of elevated contamination in the same region where 11.5 pound bombs were found during ground reconnaissance. In summary, the new methodology significantly improves the interpretability of HeliMag data when used for UXO site assessment.     

Identification of stable remanence carriers through a magneto-impedance scanning magnetic microscope

To identify the stable remanence carrier in rock samples, we conducted magnetic microscopic observations combined with conventional stepwise demagnetization experiments. The instrument, which employs an amorphous wire-based magneto-impedance sensor (30 μm diameter, 5 mm length), can document magnetic anomalies (vertical component) of the millimeter to sub-millimeter-thick rock samples with a resolution of 500 μm. Our new technique allows identification of the sources of both stable and unstable remanence components in meteorite and shocked granite samples. However, stray magnetic fields from the sensor magnetize the magnetic minerals in the sample and makes serious artifacts on the magnetic images. Although the artifacts of the induced magnetization should be solved, this new corroborative technique leads to a microscopic discrimination of stable paleomagnetic records from terrestrial and extraterrestrial materials.     

SOME NEW MAGNETIC TRANSFORMATIONS*

All magnetic transformations are governed by one simple differential relation between the observed and the transformed quantities. A magnetic map for any component, at any location, and for any given direction of magnetization can be converted into one for which any one, two, or all three parameters differ. Three new magnetic transformations are introduced: (i) reduction to equator, (ii) orthogonal reduction, and (iii) elimination of remanence. The first eliminates (or minimizes) the asymmetry and the lateral shift of the measured total field anomalies, exactly as in Baranov's reduction to pole. The second produces perfect asymmetry so that a symmetrical target lies vertically below the zero anomaly point, midway between the maximum and minimum. When remanence is a contributing factor, the direction of resultant magnetization must be known a priori in all cases, except for transformation of one component into another in the same area. Explicit working formulae are presented for reduction to equator and pole, and orthogonal reduction.     

新疆西天山东段航磁异常特征及找矿效果

介绍了高精度航磁调查在西天山东段的应用效果.在高精度航磁图上,展现出多个不同磁场背景及磁异常特征区,它们是不同构造、岩浆活动、地层及岩性分布的综合反映.该区不仅区域磁场特征明显,而且局部异常信息也极为丰富.在最新的高精度航磁图上,已知铁矿异常特征明显,为矿区外围勘探和同类地区寻找新的铁矿提供了依据.利用高精度航磁资料,新发现了五十余处铁矿异常,在2007年进行了地面查证的5处异常中,有4处见矿.这些新的铁矿异常的成功发现不仅带来了巨大的经济效益,也为今后利用高精度航磁测量在类似地区进行找矿积累了经验.     

Magnetic Surveying for Buried Metallic Objects

Field tests were conducted to determine representative total-intensity magnetic anomalies due to the presence of underground storage tanks and 55-gallon steel drums. Three different drums were suspended from a non-magnetic tripod and the underlying field surveyed with each drum in an upright and a flipped plus rotated orientation. At drum-to-sensor separations of 11 feet, the anomalies had peak values of around 50 gammas and half-widths about equal to the drum-to-sensor separation. Remanent and induced magnetizations were comparable; crushing one of the drums significantly reduced both. A profile over a single underground storage tank had a 1000-gamma anomaly, which was similar to the modeled anomaly due to an infinitely long cylinder horizontally magnetized perpendicular to its axis. A profile over two adjacent tanks had a smooth 350-gamma single-peak anomaly even though models of two tanks produced dual-peaked anomalies. Demagnetization could explain why crushing a drum reduced its induced magnetization and why two adjacent tanks produced a single-peak anomaly.
A 40-acre abandoned landfill was surveyed on a 50- by 100-foot rectangular grid and along several detailed profiles. The observed field had broad positive and negative anomalies that were similar to modeled anomalies due to thickness variations in a layer of uniformly magnetized material. It was not comparable to the anomalies due to induced magnetization in multiple, randomly located, randomly sized, independent spheres, suggesting that demagnetization may have limited the effective susceptibility of the landfill material. A different 6-acre site survey conducted on a 10- by 10-foot grid was analyzed to determine the maximum station spacing and line separation that could have been used. Essentially, all of the anomalies at this site would have been resolved by a survey conducted on a 20- by 20-foot grid and the larger anomalies would have been detected by a 50- by 50-foot grid.     

强剩磁强退磁条件下的二维井中磁测反演

强剩磁、强退磁改变了总磁化强度的大小和方向,给磁测资料解释带来困难.为此,本文利用二维井中磁测数据反演磁化强度矢量的二维分布.首先利用井中磁测的磁异常模量反演磁化强度大小的分布.然后,在已知磁化强度大小分布的前提下,拟合磁场分量,反演磁化强度方向的分布.其中,磁化强度大小和方向均用共轭梯度法求解,并通过预优矩阵改善磁化强度大小的反演效果.理论模拟说明,该方法能准确获得磁化强度矢量分布.磁化强度矢量反演结果包括感磁、剩磁及退磁的影响,这为研究强剩磁、高磁化率矿床提供了一种有效方法.     

Magnetic study of the dolerite dyke near Amarpur,Dhanbad (Bihar)

Summary The dolerite dyke of post-lower Gondwana age reported earlier by the authors [5]²) has been taken for detailed magnetic study. Seven magnetic traverses have been taken across the dyke using Schmidt vertical force variometer. Negative anomalies varying from 1400 to 2200 gammas have been observed. Magnetic susceptibility of samples from the dyke has been determined on both cores and crushed material, using the Model MS-3 susceptibility bridge. The average susceptibility of 20 samples has been found to be 1930x10^–6 C.G.S. units. Direction and intensity of remanence on 10 oriented samples have been determined by an Astatic magnetometer. The average intensity of remanence has been found to be 3.13x10^–3 C.G.S. units and the average direction has a declination of 323° and inclination-68° (up dip). The Koenigsberger ratio varies from 1.6 to 5.6. The high negative magnetic anomalies have been explained in terms of remance-that more than 80% of the anomaly is due to remance and that negative anomalies are due to negative inclination of remanent direction of the rocks. The magnetic direction for the dyke gave the position for Dhanbad as 51° south latitude in Jurassic period. This is in conformity with the deductions made by other workers from the palaeomagnetic studies of the Deccan and Rajmahal traps. The virtual geomagnetic pole in Jurassic period as deduced from the palaeomagnetism of the dyke has a position of latitude 8 1/2°N and longitude 71°W, in the southern Carribean. On palaeomagnetic evidence this dyke has been correlated with Rajmahal traps of eastern Bihar.     

给定观测精度下的点(线)源模型重力与磁力垂向识别能力研究

重、磁勘探具有效率高、成本低、工作范围广等优点,已在地球物理勘探中得到了广泛应用.前人大多在不考虑重、磁勘探观测精度的条件下进行了垂向识别能力的研究,但在考虑重、磁观测精度条件下,重力（重力异常、重力张量）与磁力（磁力异常、磁力三分量、磁力张量）对孤立异常的垂向识别能力如何则需要进行深入的理论研究.本文从重、磁场正演理论出发,以球体（点源模型）和无限延伸水平圆柱体（线源模型）为例,考虑给定观测精度条件下,以重力和磁力幅值大小与观测精度的关系来研究垂向识别能力,从而消除了背景场的影响,提高了研究结果的可靠度.通过研究表明,对于孤立异常,重力张量在浅部一定深度内比重力异常的垂向识别能力强,该深度与重力异常和重力张量观测精度的比值成正比;垂直磁化磁力张量在浅部一定深度内比化极磁力异常的垂向识别能力强,该深度与磁力异常与磁力张量观测精度的比值成正比;磁力在浅部一定深度内比重力的垂向识别能力强,该深度与地质体的磁化强度和剩余密度比值、重力观测精度和磁力观测精度比值成正比.通过重力和磁力垂向识别能力的研究将为重、磁勘探的实际应用起到指导作用.     

华北地区地磁加卸载响应比方法应用研究

运用地磁加卸载响应比方法(LURR)对华北地区23个地磁台站2008—2014年的数字化地磁相对记录数据进行计算分析,结果显示华北地区7年内发生了38次共计10组加卸载响应比异常,其中7组有震例对应,在选定的24次震例中16次有震前异常。经统计发现各次异常发生时其异常面积与最大异常强度成正比关系,各组异常内累计异常台站数量与组内地震辐射能量有一定相关性。对有震例的7组异常分析后认为多数情况下组内各次异常之间有一定联系,主要表现为位置的连续性及继承性,并且发现震中位置和异常位置分布有一定关系。     

同时考虑退磁和剩磁的有限体积法正演模拟

为分析同时考虑退磁和剩磁对磁测数据解释的影响,探讨了利用有限体积法求静磁场数值解的方法.从静磁场中的麦克斯韦方程出发,导出了有限体积法控制方程的离散表达式,对边界条件近似处理后求解方程组得到磁异常.通过与退磁改正计算结果对比,验证了方法的正确性,并分析得到忽略剩磁的相对误差与科尼斯布格比（Q）相关;利用有限体积法计算长方体模型在无地磁场情况下的磁异常和内部磁化强度,从数值模拟上说明剩磁也需要进行退磁改正,并表明退磁作用对剩磁的影响不仅与磁化率相关,而且与剩磁的方向和磁性体的形态相关;组合模型的计算结果对比表明,退磁作用对剩磁的影响还会因为临近强磁性体的作用发生改变.在青海灶火河西工区的应用说明,开展同时考虑退磁和剩磁的解释方法对准确识别强磁性岩体具有实用价值.