布格重力异常地形校正方法在微重力勘探中的缺点及其纠正方法

多年来,不论重力勘探程度如何,在布格重力异常计算中都必须经过地形改正和中间层改正。本文通过分析在计算布格重力异常时地改和中间层改正对测点的重力补偿,提出了取消中间层改正以适应微重力勘探精细解释需要的地形校正方法。该方法建立在对实际地形（岩性）的正演基础上,可以根据施工地区的地质条件合理选择重力基准面进行可变密度地形校正。使用该方法可以比较好地消除地形起伏和不均匀岩性对测点产生的重力影响,从而得到比较可信的重力异常数据。     

高精度重力测量三点联测法及其应用

<正>高精度重力测量经过野外测量、室内计算、整理发现异常后,采用作者三点联测法,于野外在异常中心测得异常区3个不同点重力场强度gA(进行地形改正,中间层改正和高程改正,未减去该测点正常重力值,下同)、gB和gC。运用重力场强度空间变化关系,求取异常源体质量中心埋藏深度;求取异常源体剩余质量;求取异常源体剩余密度、体积和矿石量。     

有限元重力任意复杂地形校正方法研究

提出了一种有限元重力任意复杂地形的校正方法,以解决重力勘探中地形改正问题。利用改进的有限元地形体正演模拟算法,计算任意地形条件下地下密度异常体在地表所引起的重力响应。研究结果表明,在任意复杂地形影响下,经过有限元地形校正后,重力响应曲线可更加直观地反映出地下密度异常体赋存状态,与模型设置相符,表明了该方法的有效性。     

用多重二次方程进行重力地形改正

本文研究了用多重二次方程的一个线性系统作重力地形改正的数字计算机方法。把这个线性系统拟合到由地形方格子所确定的和由测点本身所确定的点上,就得出一数学描述面。与数字地形模型相比,此曲面是真实地形的更好的模型。可用简单而快速的数字积分来计算这种曲面的地形改正。本文用一个理论上的例子说明,对于近测点地形改正,多重二次方程方法比手算法更精确。一崎岖地形地区的野外实例也说明此方法能够成功地应用于实际重力测量。     

山区区域重力测量中间层校正系数的确定

山区区域重力测量中,地形校正范围的选择需要大一些,才能较好的消除地形起伏造成的影响,远区的地形和中间层影响均应考虑地壳弯曲的影响。因而在进行远区校正时,不能以过测点的平面为标准,而应以过测点的球面为标准,因此,地形校正值将会有负值出现。在进行中间层校正时,应消除与地形校正最大半径范围一致的弯曲圆盘的影响,此影响不仅与盘的半径有关,而且与厚度有关。本文给出对应于不同校正半径和不同厚度弯曲圆盘的一套理论计算结果,用这些结果得到的与不同校正半径配套的中间层校正公式,可供直接查阅使用。     

重力中区地形改正系统的研制

从传统的重力地形改正方法入手,用Delphi语言编制了Windows程序,使得多年来重力中区地形改正繁重的手工数图工作能够用计算机完成,且计算精度得到明显提高。最后用甘肃1:20万昌马幅的53个重力测点进行了试算。     

重力山形异常的起因、特征与消除

按常规方法整理重力资料时,与山形相关的局部异常值,往往大于矿异常.因此,消除重力山形异常干扰,是重力勘探的重要任务之一. 起因众所周知,重力测量结果必须对高度地形(包括通常所称的中间层和地形)和纬度进行改正.由于这些改正的理论或实际应用中存在着局限性,比如通常所称的中间层改正和地形改正两者补偿的不平衡,实际高改系数和理论值(0.308毫伽/米)存在偏差,布伽密度选择不     

趋势分析在重力测量资料整理中的初步尝试

自从重力测量工作进入山区以来,对观测结果的各种外部改正已广泛地被人们所重视。这是因为大多数重力异常的解释方法只适用于在平面上测定的△g值。由于地形起伏的影响,而目前对此影响的各种改正方法又均不尽完善,给重力测量成果的地质解释造成了很大的困难。若不追究各种改正模式的准确性,那末,采用目前通用的一般公式进行布伽改正和地形改正时,直接影响精度的原因不外乎高度改正系数∨zz、中间层密度σ及地形改正最大半径R等三个因素。根据全国各地的工作实践表明,在山区,高度改正系数与理论值差别很大,其差别的量级可达几百艾维。众所周知,测区表层岩石的密度值是变化不一的,当在一个地方原为正确的数值,在另一地方就不一定是正确的。同样,由于中间层密度的差异或选择不当,试图单纯地通过扩大改正范围的途径来提高地形改正的精度,又因引入了新的误差而使这一工作毫无益处。上述三种因素的存在,会使布伽异常图产生畸变。也就是说,很容易出现与我们感兴趣的深部物质无关而仅与地形相关的所谓“山形异常”。     

基于VC~( )的重力近中区地形改正可视化程序设计

从传统的重力地形改正方法入手,用VC~( )语言编制了重力地形改正可视化程序。它能用于重力近中区地形改正,并能满足重力地改的精度要求,使得多年来重力近中区地形改正繁重的手工数图工作能够用计算机完成,且计算精度和速度得到明显提高。通过人机对话的形式(操作界面),可直接计算出近、中区的地形改正值。     

重力数据库各项外部改正的计算

本文介绍的是在重力数据库系统中配备的一套重力各项外部改正计算的方法和程序,其中地形改正和均衡改正程序将远区改正范围划分为三个区:远一区为1或2公里至20公里,采用平面公式,高程数据网度为1公里×1公里;远二区为20公里至166.7公里,采用球面公式,高程数据网度为5′×5′;远三区为166.7公里至全球,采用球面公式旋转椭球体模型,为全球1°×1°高程数据网,各区一律用园域接口。为便于用户选择,每区备有多种方法。此外还备有高度改正,中间层改正和正常改正程序。用这个系统可以计算自由空间重力异常,布格重力异常和均衡重力异常值。     

The Rapid Inversion of 3-D Potential Field and Program Design

The application of three-dimensional inversion of gravity and magnetic fields is very important not only in geophysical researches, but also in the study of geological structures. A formula of potential field in frequency-domain, developed by Parker in 1973, can be used as a rapid and effective algorithm in gravity and magnetic inversion. The technique has been improved then by Oldenburg, Sprenke, Feng and others.In addition to a brief introduction of Parker's algorithm and its applications, this paper includes the following five parts: basic computational techniques, inversion of single layer, convergence and constraints, simultaneous inversion for density and topography as well as inversion of multilayers. The authors present relevant practical iterative formulas and its varieties when density distribution varies with depth in linear or exponential relation. In order to maintain computation stability and speed up iteration convergence, some approaches are taken in the program design, for instance shifting lower interface of the studied layer, inverting corrections of topography, reducing grid boundary effects and utilizing low-pass filter. With the consideration of the nonuniqueness of the inversion, a method of using seismic data to constrain the range ofpossible models is discussed. It is pointed out that the density variation generates less effects than those of topography on the spectrum of gravity anomaly in second order. Therefore density contrast and topography can be inverted simultaneously by an alternative weighting iteration. By analogy, the inversion of multilayer model can be done in the above procedure. An approach of model decomposition is useful in the computation of multilayer model. The techniques discussed in the present paper for gravitational field are also valid for magnetic field.     

资源三号数据在重力中区地形改正中的应用

针对我国资源三号卫星立体影像数据,利用GPS控制点,结合前视、下视、后视区域网平差精化有理函数模型,探讨了资源三号卫星立体影像数据用于重力中区地形改正的高精度DEM生成方法。通过1：1万高精度DEM数据进行地改实验验证表明：资源三号卫星立体影像数据提取的DEM可以满足1：20万区域重力测量中区地改精度要求,为我国重力测量中区地形改正提供了一条有效途径,拓展了资源三号数据在区域重力测量中的应用。     

Reactive infiltration instability of a granitization front during the generation and development of granite-gneiss domes

The origin of granite-gneiss domes is traditionally attributed to gravity tectonics, the ascent of granite-gneiss diapirs in a gravitational field owing to a relative decrease in the density of granitized rocks compared with their protolith. This is usually considered by the example of a two-layer medium with a lower layer of granitized rocks overlain by a denser protolith layer; the development of gravitational instability in the system results in the ascent of a granite-gneiss diapir. However, the diapiric process can be initiated only if Archimedes?? buoyancy forces at the roof of the granite-gneiss layer will overcome the resistance of the protolith rocks related to their long-term strength. Under the conditions of plastic deformations, this requires the existence of a large-scale irregularity in the relief of the layer boundary, namely, an antiform cusp in the roof of the granite-gneiss layer. The model is based on the assumption that such antiforms appear owing to the reactive infiltration instability of the morphology of the granitization front caused by an increase in the fluid permeability of granitized rocks compared with that of the protolith. The results of computer modeling support the geological feasibility of the reactive infiltration mechanism of the generation and development of the protodiapiric forms of the granitization front triggering the development of the diapiric process of the gravitational upwelling of granite-gneiss domes. The model of a protodiapir stage allows us to consider dome formation as a result of the development of two sequential instabilities: the reactive infiltration instability of the granitization front related to an increase in the permeability of the transformed rock followed by the gravitational instability related to a relative decrease in rock density.     

青藏高原重力异常与地形高程的负相关校正

针对消除青藏高原重力异常与地形高程呈负相关关系所引起的假异常,提出了均衡校正和残余负相关校正相结合的一套具有可操作性的校正方法,并对青藏高原可可西里地区重力异常数据进行了处理,效果明显,验证了方法的有效性.     

Combined geological and gravimetric mapping and modelling for an improved understanding of observed high-resolution gravity variations: a case study for the Global Geodynamics Project (GGP) station Moxa, Germany

Geodynamic observatories around the globe continuously monitor signals like gravity, tilt and strain as a function of time. However, global signals are often masked by local effects, caused by the direct surroundings of the station, including the local geological setting. This link is well established for superconducting gravimeters (SG) that observe the gravity field variations at very high resolution. An enhancement of the SG time series by the application of local correction is exemplarily shown here in a very practicable procedure for the Geodynamic Observatory Moxa, Germany. We show how the combination of geological and gravimetrical mapping and modelling around Moxa results in a significant correction of the original gravity data, as can be proven by comparison with the satellite-derived gravity field. Detailed geological mapping of the observatory surroundings, including measurements of fold axes, foliations and joints, was the basis of the present study. The fold structure in the area of interest was interpreted by geometrical 3D modelling. The complete representation of different rock types in space also provides a better understanding of the local hydro-geological situation. Using a combination of the 3D geological model with the high-resolution Bouguer map of the observatory surroundings, we developed a 3D density model. This model enables the correction of small gravity effects caused by mass variations close to the SG, in particular local hydro-geological mass changes. Thus, the procedure presented here, based on a close connection of geology and gravimetry, is a powerful tool for the reduction of local gravity effects on SG recordings. It should be applicable to SG stations worldwide, where similar hydrologically driven mass changes can be assumed.     

重力场定义的澄清

《朗曼现代英文词典》(LongmanModernEnglishDictionary)、《牛津高阶英汉双解词典》(OxfordAdvancedLearner’sEnglish ChineseDictionary)、《韦氏词典》(Merriam Webster’sNewCollegiateDictionary)、作为地球物理专业词汇定义源的《勘探地球物理百科词典》(EncyclopedicDictionaryofExplorationGeo physics)以及中国的一些重力教科书、专著及词典 ,把重力场定义为重力或重力作用存在的空间 ,重力效应可以测量的空间 ,即 :力或重力存在的空间。这个定义不同于国外英文地球物理教科书、专著及中、英、俄文场论教科书对重力场的定义 :空间中的重力。定义重力场为重力存在的空间 ,混淆了“场”本身及“场域”的概念 ,并不是一个标准的物理或地球物理定义 ,是一种误导。物理场是空间中存在的一种物理作用或效应 ,分布于引起它的场源体周围。两个物体之间存在着的相互作用力 ,通过每个物体引起的引力场给予另一个物体。重力场可以定义如下 :地球内部及其附近空间一点处存在的重力作用 ,或单位质量受到的重力。重力场是一种力或力场 ,存在于地球表面及其附近的空间。重力场不是空间 ,重力场的测量应当是在重力场存在的空间或场域中 ,而不是在重力场中进行。     

Using Newton's law and geophysical bounds on mass density contrast to ensure consistency between gravity and height data

In this paper we advocate the use of Newton's law of gravitational attraction to ensure perfect consistency between gravity and height data. Starting with the absolute gravity on the topography we decompose this signal into a number of quantities associated with physics of the system. To model gravitational attraction from topography we use DTM and Newton's law of gravitational attraction. A residual part of the gravity signal is interpreted as inconsistency between gravity and heights. In the paper we discuss a method by which such inconsistency (at least in principle) can be decomposed into a “gravity error” and a “terrain error”. In practice such separation is not possible because the two types of error are nearly 100% correlated. The inconsistency can be interpreted as a measure of ambiguity of the gravity-terrain models which are consistent with a set of measured/interpolated data. We discuss the influence of such ambiguity on the accuracy of the geoid for the investigated area of Jutland, Denmark.     

由野外实测数据直接生成MAPGIS地质基础图件方法

传统纸介质手工制图存在信息实时再现滞后、共享交换不便等弊端,即便目前普遍使用计算机制图,也只是对纸介质底图进行二次描绘,不是真正意义上的计算机数字化制图和专业应用.因此,由野外实测数据直接进机处理生成地质基础图件,已成为专业人员在实际工作中急需解决的实际问题.笔者尝试以中国地质大学开发的MAPGIS6.6为主,辅以常用图表处理软件等,将原始数据转换成MAPGIS明码格式文件,导入成图系统,经系统处理直接成图,基本解决了野外实测数据直接进机处理生成地质基础图件的问题,其成图精度高,基本图形、数据共享,成果信息实时再现,能够进行基本的空间分析,可实现信息全息化,成图质量可通过源数据检查等.     

Modelling the geoid and sea-surface topography in coastal areas

This paper looks at the relation between the time-averaged level of the sea surface and a gravimertic geoid, as determined in coastal areas. Measurements in local regions can now be accurate enough to demonstrate that the geoid and mean sea level are not even parallel to each other, let alone identical. The accuracy and pattern structure of surface gravity data in some shelf seas is comparable with those on land, so that a marine geoid can be derived from surface data without using satellite altimetry. The geodetic objective is then to combine the two to determine sea surface topography. In principle, gravimetric studies provide the absolute datum so that local oceanographic models on the shelf can be combined with sea surface topography models related to the global ocean circulation. In contrast, sea surface topography information near deep ocean coasts must come from external sources and satellite altimetry used to give the gravity data needed to offset the less good coverage by ship-borne gravimetry.Marine Bouguer anomalies enable two specific problems of gravity anomaly patterns near the continent ocean transition to be overcome. The necessary extension of Stokes' condensation reduction is developed and illustrated along a north-south profile from the Mediterranean across the Cote d'Azur. The effect on gravity of deep ocean water introduces a geoid correction in the form of a dipolar ridge whose amplitude at the shore is about 11 cm. In addition to geostrophic currents, a semi-quantitative model for the thermohaline effects on sea surface topography is discussed in relation to sea level differences between the Atlantic and Mediterranean.In considering appropriate algorithms for local geoid computation, Kirby's Iterative Fourier Combination routine for combining altimetry and surface gravity is extended to account for global sea surface topography. The impact of very fast spherical harmonic analysis algorithms is discussed and a simple physical model is given which explains the short coherence lengths found for the global gravity field. This necessary assumption for any local geoid computation was hitherto purely empirical.Finally, the use of land data such as tide gauges, ellipsoidal heights from GPS, and orthometric heights from first order levelling are reviewed as ways of corroborating geodetic estimates of sea surface topography and its relation to levelling datums. Successful examples are given from southern England.