In this paper we expand on a new concept for potential field processing and interpretation, the potential field tilt, which we introduced in an earlier paper. The tilt angle is defined in terms of the ratio of the first vertical derivative of the potential field to the horizontal gradient of the field. This measure has the property of being positive over a source and negative elsewhere. The tilt angle is compared with other edge detection measures such as the horizontal gradient, the second vertical derivative and the analytic signal and found to have the added advantage of responding well to both shallow and deep sources. A map of the tilt angle is provided to illustrate its use in recognizing the horizontal location and extent of sources.

Abstract The development of electronic magnetometers, i.e., the proton-precession and fluxgate instruments, for use in ground magnetic surveys has permitted the measurement of the first-vertical derivative of the total field, or of the vertical component of that field, with negligible addition to the total cost of the survey. The gain in information is, however, significant. Curves for the vertical gradient over a vertical contact, point pole, and finite dipole are presented. The vertical contact is outlined by the zero contour for the vertical gradient of the vertical component, and the depth of burial is half the horizontal distance between the positive and negative maxima. The depth of burial of the point pole and finite dipole is approximately equal to the horizontal distance between the negative half-maximum points on the vertical-gradient curves.

Abstract The total magnetic field values over an area can be represented exactly by a double Fourier series expansion. In this analysis, such an expansion is used to evaluate very accurately the fields continued downward and upward from the plane of observation and the vertical derivatives of the total field. This harmonic expansion of the anomalous total field makes it possible to calculate, with exceptional accuracy, the field reduced to the magnetic pole and its second derivative. The results of the calculations are free from the effect of the inclination of the earth's main geomagnetic field and that of the polarization vector, at all magnetic latitudes and for all possible directions of polarization. In order to determine the influence of remanence on the above field, a number of anomalies caused by rectangular block-type bodies with known polarization are reduced to the magnetic pole, correcting only for the obliquity of the earth's normal field. It is concluded from a study of these anomalies that the interpretation of magnetic data based on the assumption of rock magnetization due solely to induction in the earth's field may yield erroneous results, particularly when remanence is important.

Measures of the local phase of potential fields can be a useful aid to their interpretation. There are several variations in use, such as the tilt angle, tilt derivative and the Theta map. This paper compares the results of these filters, and introduces some new phase-based filters which show improved performance as edge detectors in different ways. The filters are demonstrated on synthetic gravity data and on magnetic data from Australia. Source code in Matlab format is available from the server at: www.iamg.org.

<p>边界识别是进行位场数据解释时一项必不可少的任务.现有的边界识别滤波器存在识别边界发散和深部地质体边界模糊的缺点.本文提出增强型均衡滤波器,可有效地改善上述缺点.该滤波器是利用不同阶导数之间的组合来进行地质体边界的识别,并在运算中引入一种计算高阶垂直导数的稳定算法.通过理论模型试验证明增强型均衡滤波器能使浅部与深部地质体的边界同时清晰地显示,且相对于其它边界识别滤波器能更加准确和清晰地识别出地质体的边界.最后将增强型均衡滤波器应用于实测位场数据的解释,根据其识别结果可容易地划分出断裂的水平位置及不同地层之间的界线,并能发现更多的细节信息.</p>

为了突出显示重磁场中地质体分布、断裂构造特征等信息,使图像显示错落有序、层次分明、清楚直观,有利于解释人员从不同角度认识重磁场异常特征.本文通过分析倾斜角概念,根据反余切函数特性,提出了扩展的倾斜角(iTdr)和倾斜角总水平导数(iTdr_Thdr)方法,来增强重磁异常信息,突出异常形状特点,以便于识别重磁异常中地质体边界和提取地质体分布、断裂构造平面展布特征等信息.理论模型和实际资料对比分析表明该方法简单、实用、具有较好的识别效果和较高的分辨能力,能够获取丰富的地质信息,对识别地质体边界、划分大地构造单元、确定断裂带和地质构造走向等具有实际意义.

Abstract A two-dimensional mountainous mass flow dynamic procedure solver (Massflow-2D) using the MacCormack-TVD finite difference scheme is proposed. The solver is implemented in Matlab on structured meshes with variable computational domain. To verify the model, ...

边界识别是位场数据解释的一项基本任务.现有边界识别方法大多是 基于水平与垂直导数的高通滤波器,但垂直导数的计算会明显地增大噪声的干扰.为了改善这一问题,本文提出了一种新的边界识别滤波器,该方法是利用不同阶水 平导数之间的线性组合来进行地质体边界的识别,由于该方法不需要垂直导数参与计算,因此其输出结果较稳定.理论模型试验表明,该方法能够更加清晰的识别地 质体的边界,且与其真实边界相吻合.最后将其应用于实际数据的处理中,其结果清晰地反映出断裂的位置及构造之间的界线,并能识别出更多的细节信息.

Many of the existing balanced edge detection filters of potential field data only use the feature that the vertical derivative is zero above the source edges to recognise the source edges. This will produce spurious edges in the interpretation of potential field data. In order to solve this disadvantage, a new format of the edge detection filter is presented, which produces maximum values only when the horizontal derivative is a maximum and the vertical derivative is zero, so the new filters will not produce spurious edges, and will provide more accurate results. The proposed filters are tested on synthetic potential field data. The recognised edges are shown to be consistent with the true edges, and do not produce additional edges. Moreover, the proposed filter suppresses the effect of noise, and displays the edges more clearly compared to previous edge detection filters. It is also applied to real magnetic data to obtain the horizontal locations of iron ore.

边界检测在地球物理位场数据解释中占有重要位置.现有的传统边界识别方法有的不能同时显示不同振幅的异常边界,有的虽然能均衡不同振幅的异常,但识别出来的边界信息中含有一些额外的错误的边界信息,尤其是当测量的异常中同时含有正异常和负异常时.目前已有的去除额外错误边界信息的方法存在着一定的人为主观性.为了解决这些问题,本文定义了加强解析信号倾斜角来进行地质体边界识别.通过模型试验证明了该方法不仅能同时清晰地识别深部和浅部地质体的边界,而且能有效地避免引入一些错误边界信息.最后将该方法应用到四川盆地的重力异常数据中,并取得了良好边界结果.

61A newly technique was presented to balance the edges.61The new method can balance the amplitude well and get a higher resolution.61A parameter p can avoid bring false edges and reduce the noise effect.

位场全张量梯度数据以其信息量大、含有更高频的信号成分,能更好地描述小的异常特征等优点在地球物理领域中得到广泛应用.边界检测是位场解释中不可缺少的任务,需要新的边界探测器来处理位场梯度张量数据.为了充分利用位场梯度张量数据的多信息成分,本文定义了方向总水平导数和加强方向总水平导数,并利用其定义新的边界检测器.为了能同时显示不同振幅大小异常的边界,本文对其进行了归一化处理.通过模型试验,证明了归一化方法能更加清晰准确地显示浅部和深部的地质体边界信息.最后将该边界检测方法用于加拿大圣乔治湾实际测得全张量重力梯度数据和中国朱日和地区的磁异常数据中,并得到了较好的边界检测结果.

Abstract — Rinsing experiments with mouthwashes containing zinc ions, hexetidine and a combination of hexetidine and zinc ions were performed with a group of 10 vohmtcers. The amount of plaque was assessed after rinsing with the test solutions for 4 days during which mechanical toothcleaning was discontinued. Significantly improved inhibition was observed by the combination of hexetidine and zinc ions compared with the two agents used separately. In vitro bacteriaal tests showed that hexetidine and zinc ions had a synergistic inhibitory effect on the growth of Streptococcus mutans.

Evaluation of higher derivatives (gradients) of potential fields plays an important role in geophysical interpretation (qualitative and/or quantitative), as has been demonstrated in many approaches and methods. On the other hand, numerical evaluation of higher derivatives is an unstable process it has the tendency to enlarge the noise content in the original data (to degrade the signal-to-noise ratio). One way to stabilize higher derivative evaluation is the utilization of the Tikhonov regularization. In the submitted contribution we present the derivation of the regularized derivative filter in the Fourier domain as a minimization task by means of using the classical calculus of variations. A very important part of the presented approach is the selection of the optimum regularization parameter we are using the analysis of the C-norm function (constructed from the difference between two adjacent solutions, obtained for different values of regularization parameter). We show the influence of regularized derivatives on the properties of the classical 3D Euler deconvolution algorithm and apply it to high-sensitivity magnetometry data obtained from an unexploded ordnance detection survey. The solution obtained with regularized derivatives gives better focused depth-estimates, which are closer to the real position of sources (verified by excavation of unexploded projectiles).

<p>位场垂向导数大量应用于位场数据处理与解释中.当前广泛采用的位场各阶垂向导数换算方法为基于Laplace方程并结合波数域和空间域方法的具有递推特性的ISVD(integrated second vertical derivative)算法.本文在位场垂向导数换算的正则化方法和径向平均功率谱的基础上,提出一种位场各阶垂向导数换算的新正则化方法.新正则化方法仅需通过分析位场径向平均功率谱来确定一个截止波数,即可稳定换算位场各阶垂向导数.理论模型和实测数据实验结果表明:(1)新正则化方法物理意义明确、计算简单,且各阶垂向导数换算的稳定性和精度明显优于ISVD算法;(2)在用新正则化方法求得各阶垂向导数的基础上,利用泰勒级数法可以获得大深度、高精度的位场向下延拓结果.</p>

本文讨论场位解析延拓的稳定化算法。首先叙述问题的古典提法,并且为以后作准备,将它化成另一类不适定问题。接着建立问题解的连续依赖性估计。然后根据这个估计式,将问题化成求解一个条件变分问题。最后利用正则化方法解这个变分问题,得到问题解的一个稳定化的计算公式。

The four frequency response formulas of rcgularization methods for downward continuation of potential fields are discussed and their characteristics are analyzed. These methods can effectively restrict the oscillations due to the measuring errors or the high frequency disturbances. The trend of downward continuation is stable. The results of various trials are given.

The magnetic method has been proven to be a successful geophysical tool for the detection of unexploded ordnance (UXO). Aeromagnetic surveys are advantageous since they can acquire data over large areas. The downside is that magnetic anomalies due to multiple metallic targets can overlap significantly due to flight height restrictions. Such overlap combined with the acquisition noise may significantly decrease the signal-to-noise ratio of data. These adverse effects can mask the true level of contamination at a site during the initial assessment based on the magnetic method as well as decrease the overall effectiveness of discrimination during the active clearance stage. We propose a method to ameliorate these difficulties using stable downward continuation, which reconstructs the field at a lower observation height from the observed data. The stable algorithm formulates the downward continuation as an inverse problem and incorporates the expected power spectrum of UXO anomalies. The power spectrum preserves the spectral properties and subdues the amplification of high-frequency noise. Synthetic and field examples show that the algorithm can reliably reconstruct the magnetic anomaly at the ground surface within the limitation imposed by the noise. The reconstructed field exhibits significant enhancement compared to the original data.

<p>解析延拓是一种广泛应用的位场处理方法,向下延拓可以压制深部地质体的影响,突出浅部异常。但是,向下延拓滤波因子是一个高通滤波器,会造成下延结果震荡,从而限制了该方法在实际资料中的应用。文中详细介绍并实现了迭代Tikhonov正则化向下延拓方法,在理论模型上将该方法与传统频率域延拓方法进行对比,表明迭代Tikhonov正则化向下延拓方法的有效性;并将该方法应用于青海尕林格铁矿区磁测资料的处理解释中,下延结果与钻探情况相符,说明在厚覆盖层的勘查区中,运用迭代Tikhonov正则化向下延拓方法能够有效地提高资料处理解释的效果。</p>

<FONT face=Verdana>研究地质体的边缘位置是重、磁位场数据解释永恒的主题，也是其优势.最近几年，国内外利用重、磁位场进行地质体边缘识别研究的文章明显增多，但没有作者系统整理和对比各方法的优点和缺点，给使用者带来诸多不便.本文首先将现有重、磁位场边缘识别方法分为数理统计、数值计算和其他三大类，并概述了各类方法的研究现状；之后较详细总结了数值计算类中垂向导数、总水平导数、解析信号振幅、倾斜角、<EM>θ</EM>图这5种基本的边缘识别方法以及在这些基本方法之上发展起来的诸如倾斜角总水平导数、增强解析信号振幅等方法的研究历史和应用效果；并用理论模型对比了几种主要边缘识别方法的识别效果.通过以上总结、对比和分析，指出了重、磁位场边缘识别方法使用中需要注意的问题以及将来的研究重点及发展方向.</FONT>

Edge detection is a useful tool in the interpretation of potential field data, and the existing edge detection filters are almost functions of first-order horizontal and vertical derivatives. We propose step-edge detection filters to improve the resolution of edge detection results, which use the functions of different-order derivatives to accomplish the edge detection task. We demonstrate the proposed filters on synthetic potential field data, and the results show that the new methods can recognize the edges of the sources more precisely and clearly. We also discuss the application effect of different step-edge detection filters. Lastly, we apply the proposed filters to real potential field data, and the recognized edges of the stratigraphic markers are more precise and clear.

Edge detection is a requisite task in the interpretation of potential field data. There are many high-pass filters based on horizontal and vertical derivatives in use, such as total horizontal derivative, tilt angle, theta map, et al. In this paper, we present a new edge detection filter, which uses the combination of the different order horizontal derivatives to delineate the edges of the sources, called improved local phase (ILP) filter. The new filter is computationally stable, as it does not need the computation of the vertical derivatives of potential field data. The new filter is tested on synthetic and real potential field data. The resolving power of the ILP filter is tested by comparing the results with those obtained by the other filters. The advantage of the ILP filter in the edge detection of potential field data is due to the fact that it can display the edges of the causative sources more precisely and clearly, and can bring out more subtle details.

地质体构造边界位置的确定是位场数据解释中的一项重要工作,现有很多基于位场梯度张量数据的边界检测滤波器,但存在识别边界位置模糊且无法均衡深浅地质体异常的缺点.本文定义了位场数据的三维构造张量,并提出基于位场构造张量的边界滤波器.为了同时显示不同振幅异常的边界位置,对新定义的滤波器进行归一化处理.在高阶均衡滤波器的计算中需要计算位场的垂向高阶导数,本文引入一种计算的稳定算法,基于拉普拉斯方程利用位场水平导数求解垂向导数,可减小垂向导数计算中产生的误差.将定义的滤波器应用到合成的重磁数据中证明了新方法相比传统的滤波器能更加清晰、准确地圈定边界位置,而且针对同时含有正负异常的地质情况,可避免产生额外的错误边界.最后将新的滤波器应用到实测的重磁数据的解释中,结果显示基于构造张量的滤波器可更准确清晰地划分出断裂的边界位置,发现更多的构造细节.

边界检测在地球物理位场数据解释中占有重要位置.现有的传统边界识别方法有的不能同时显示不同振幅的异常边界,有的虽然能均衡不同振幅的异常,但识别出来的边界信息中含有一些额外的错误的边界信息,尤其是当测量的异常中同时含有正异常和负异常时.目前已有的去除额外错误边界信息的方法存在着一定的人为主观性.为了解决这些问题,本文定义了加强解析信号倾斜角来进行地质体边界识别.通过模型试验证明了该方法不仅能同时清晰地识别深部和浅部地质体的边界,而且能有效地避免引入一些错误边界信息.最后将该方法应用到四川盆地的重力异常数据中,并取得了良好边界结果.

Theta图是利用位场(重磁)数据识别边界的常用方法,其表达式为重磁异常水平变化与垂直变化的比值函数.该方法计算浅源地质体边界的效果较好,而由于深源位场数据在换算过程中会产生趋同效应,在深源地质体识别应用中计算结果不准确,为此,本文提出Theta-Depth法并进行地质体埋深的计算.首先给出直接利用Theta图像进行场源体深度估算的方法,然后推导出基于Theta导数的线性方程来自动估算场源位置参数,本文方法可有效地利用Theta图像的特征为约束条件来提高反演结果的精度.理论模型试验证明本文提出的Theta-Depth法能有效地计算出场源体位置和深度.将该方法应用于满都拉地区实测磁数据的解释,帮助圈定了矿脉的分布.