重力基点网平差中的间接平差

笔者将间接平差方法引入重力基点网平差中。将基点网中各个基点的重力平差值设为与其近似值有关的函数;利用最小二乘准则约束参数函数,建立误差方程;求出平差值。计算结果显示,传统条件平差以及间接平差方法的平差结果相同,但是间接平差的计算过程更有规律性,便于编程计算,适用于由多基点、多边段组成的复杂基点网。     

用条件观测平差法进行重力基点网的平差

条件观测平差法(以下简称条件平差法)是平差方法的一种。它具有方法严谨、计算精度高等特点。尤其适用于以闭合环形式联测的重力基点网的平差。但由于它的计算较复杂,特别在观测值个数较多时,计算工作量很大,且极易出错,影响了方法的使用。但是在采用电子计算技术后,计算的速度和精度就可大大提高。去年,我队根据条件平差的原理编制了DJS—6(108)机和M—160Ⅱ机程序(适用于处理大数据量),分别在108机和M—160Ⅱ机上完成了河北省Ⅰ级重力基点网的平差(该网包括20个基点,26个重力增量值,分六个闭合环)。计算了各边重力增量的平差值、各基点重力值的中误差以及各项检验计算。全部计算及打印时间在108机上是一分半钟,在M—160Ⅱ     

云南滇西南地区二级重力基点联测结果报告

完成单位 :云南省地调院地球物理地球化学调查所内容简介 :建立滇西地区二级重力基点网以满足该区 1∶2 0万区域重力调查工作的需求 ,完成面积 1 0 5 0km2 ,滇西南地区重力二级基点网联测 1 5个闭合环 ,1 2 2个重力二级基点 ,其中 1 6个支基点 ,最少边段数 8条 ,连续支基点≤ 2个。网上基点均取得了 2个以上的合格独立增点。超额完成设计任务。专业人员对原始资料进行专门性检查 ,查阅了实际材料图 ,重力仪仪器性能试验记录 ,重力野外观测记录本 ,二级重力基点档案 ,二级重力基点成果表。基点网平差示意图等到 ,并抽查计算了基点网增量数 36…     

波波夫平差法的VB实现及Surfer自动绘图

利用VB语言实现了重力基点网平差的波波夫平差程序,并利用Surfer Automation的方便特性,在VB程序中调用Surfer软件自动绘制重力基点网平差示意图。实践表明,利用程序实现的波波夫平差程序具有方便、精确的特点,而Surfer自动绘图则将人从手工绘图中解放出来,并具有快速、美观的优点。     

MATLAB在重力基点网平差中的应用

利用MATLAB语言编写M文件,可以读取指定文件名下的Excel文档中基点网平差时所运用的基本参数进行计算,得到准确的平差结果;该M文件使用时不需要打开源程序,在Excel文件中输入相关数据后,打开MATLAB运行界面中直接输入M文件名就可以进行平差计算,使用简单方便.     

重力基点网的广义逆矩阵平差法

重力基点网平差计算通常采用的是波波夫多边形平差法,此法虽简便易懂,但欠严密.现介绍一种利用广义逆矩阵理论进行平差的方法,它是适合于电子计算机计算的一种方法.广义逆理论是矩阵理论在近廿年来最新成就之一,是研究现代控制理论、最优化理论、网络理论、数理统计等学科的重要工具.     

安徽省重力基点网的布设及其成果意义

在国家2000网重力基本点的控制下,在全省范围内布设了80个省级重力基点,组成了覆盖全省的重力基点网。基点网的建立可以使今后全省重力测量成果保持统一,全省重力测量成果也将成为全国重力测量成果的一个组成部分,因此,全省重力基点网的建立具有十分重要的意义。     

奇异值分解在重力网平差和精度计算中的应用

本文利用奇异值分解法求重力网平差的条件方程以及计算各基点平差值的均方误差。并给出了与计算基点平差值权倒数有关的递推公式。最后给出了本方法的程序框图和算例。     

MATLAB及其在重力基点网平差中的应用

MATLAB作为最优秀的数学软件之一，在国内外工程技术界产生愈来愈大的影响，其强大的数据计算和图形显示功能尤为突出。复杂的物探重力基点网平差计算通过用MATLAB的矩阵计算功能，变得简单易懂。而编制的MATLAB的M文件程序，计算快速准确。相信MATLAB在物探数据处理工作中将发挥重要的作用。     

重力测量基点网平差的数值计算方法

目前,在重力测量中,基点网平差多采用波波夫多边形平差法,也就是逐次渐近的图解平差法。这个方法的最大优点是比较直观和形象,直接在基点网的分布示意图上逐次分配闭合差。然而,这种方法有缺点,就是其分配过程比较繁琐和复杂,尤其在闭合圈数较多时更为突出,稍一疏忽,便容易出错,而且平差过程中的错误,只有在最终结果中才能发现;另外,此方法也不便在计算机上实现平差运算。     

三角平面拟合法在重力地形改正中的应用

介绍了三角平面拟合法在重力勘查近中区地形改正中的应用。该方法应用三角平面拟合通过地形图DEM模型数据（或散点模型数据）直接内插求得地形改正量板模型的结点高程数据,实现了地形改正的电脑化作业。     

利用VB编程完成基点网联测中的各项计算

整套重力计算程序包括了除“地改”以外的所有项目的计算，在这篇文章中我们先仅介绍了“测区参数初始化”及“基点网联测”(采用三程小循环方式)的计算方法。“测区参数初始化”功能可生成gdw．csh初始化文件(该套程序的各项功能都要读取该文件中的相关参量)；“基点网联测”功能可计算基点网联测的各项精度，对联测进行平差，求出各分基点绝对重力值。     

重力近区地形改正精度探讨

在大比例尺重力勘探工作中,近区、中区地形改正误差对重力总精度影响较大。在实际工作中,近区域地形改正一般采用实测或用地形图读图计算;中区地形改正一般采用地形图读图计算,《大比例尺重力勘查规范》只考虑地形图高程精度对重力总精度的影响,忽略了地形图平面坐标精度对重力总精度影响。这里从锥形、扇形基本地形改正公式推导出发,探讨不同比例尺,不同高程,平面精度对重力总精度的影响,并提出了不同地形改正精度对地形图比例尺及高程,平面精度要求建议。     

High-resolution regional gravity field model of Pakistan based on best residual terrain model (RTM) of topography and interpolation techniques

This study focuses on the development of absolute gravity model for Pakistan based on best possible residual terrain model of gravity using residual terrain modeling technique. The datasets used for the development of model are observed gravity, global gravity models, and Shuttle Radar Topographic Mission (SRTM30) elevation data. The residual terrain modeling technique has been used in the remove-restore procedure for smoothing the observed gravity field. Different topographic elevation models were tested in the model selection and one best possible model with minimum mean and standard deviation was selected for residual terrain effects. Least square collocation technique has been used for quality control and error estimates. The best possible covariance model was established from residual gravity for onward prediction of gravity anomalies at the earth surface for error and prediction analysis. The residual terrain effect of gravity, value of free air anomaly from EGM96, and observed free air anomaly are added to normal gravity to compute the absolute gravity at earth surface. The prediction of these parameters is made by employing Lagrange interpolation with least square adjustment. The results are compared with ～5% randomly selected data points not utilized for the development of covariance function and/or model development. Spline interpolation technique has also been used for the prediction of gravity field-related parameters. Lagrange interpolation exhibits relatively superior results over spline-based interpolation. This is as per expectation due to the reason that additional gridding for spline interpolation filters the signal part as well. This fact is evident from the results of spline interpolation of Grid-I and Grid-II with relatively better prediction results in Grid-I. This version of the model is capable of prediction having limiting error of 30 mGal. The predicted results show that 96.16% of prediction data falls within above-mentioned limit with Lagrange interpolation technique with least square adjustment for whole Pakistan area. The adverse effect of gridding is absent in case of Grid-I due to relatively flat areas and predicted data matches totally with control values for both spline as well as Lagrange interpolations. However, in case of Grid-II which includes high mountains of Himalaya, gridding effect is present and the accuracy of the predicted results falls to ～92%. The computed results have been compared with absolute values predicted using EGM96 and EGM2008 models as well. The gravity field recovered with PAKGM model is much better, i.e., ～ 96.16%, than both with EGM96 and EGM2008 which is about 85% only.     

Detecting rift basins in the Evans Ice Stream region of West Antarctica using airborne gravity data

A total of 11,500 line km of aerogravity data have been used to construct an free-air gravity anomaly map for the Antarctic region that may contain the microplate boundary between the Haag Nunataks block and southern Antarctic Peninsula. Along-line free-air gravity anomaly data resolved wavelengths of 9 km or greater with better than 5 mGal accuracy. Coincident radio echo soundings provided data to construct a digital terrain model. The gravity effect of the terrain was calculated by Gauss–Legendre quadrature (GLQ) and spectrally correlated with the free-air gravity data. Terrain-correlated free-air anomalies related to possible isostatic imbalances of the crust were separated from terrain-decorrelated anomalies that may reflect intra-crustal density contrasts. Subtracting terrain-correlated free-air anomalies from the gravity effects of the terrain yielded compensated terrain gravity effects (CTGE) that were used to model the Moho by inversion. The results indicate moderate but significant crustal thinning below the Evans Ice Stream that is consistent with an extensional origin for the deep, wide, steep-sided trough that contains the ice stream as well as the continued elevation of the footwall flank of the basin. Changes along the axis of the rift, both in the gravity anomaly field and the distribution of Moho topography, can be explained by processes associated with continental lithospheric extension. Subsequently, many of the features produced by extension have been modified by glacial erosion and the sub-ice topography and gravity data reflect this.     

Crustal structure of the western part of the Southern Granulite Terrain of Indian Peninsular Shield derived from gravity data

The Southern Granulite Terrain (SGT) is composed of high-grade granulite domain occurring to the south of Dharwar Craton (DC). The structural units of SGT show a marked change in the structural trend from the dominant north–south in DC to east–west trend in SGT and primarily consist of different crustal blocks divided by major shear zones. The Bouguer anomaly map prepared based on nearly 3900 gravity observations shows that the anomalies are predominantly negative and vary between −125 mGal and +22 mGal. The trends of the anomalies follow structural grain of the terrain and exhibit considerable variations within the charnockite bodies. Two-dimensional wavelength filtering as well as Zero Free-air based (ZFb) analysis of the Geoid-Corrected Bouguer Anomaly map of the region is found to be very useful in preparing regional gravity anomaly map and inversion of this map gave rise to crustal thicknesses of 37–44 km in the SGT. Crustal density structure along four regional gravity profiles cutting across major shear zones, lineaments, plateaus and other important geological structures bring out the following structural information. The Bavali Shear Zone extending at least up to 10 km depth is manifested as a plane separating two contrasting upper crustal blocks on both sides and the gravity high north of it reveals the presence of a high density mass at the base of the crust below Coorg. The steepness of the Moyar and Bhavani shears on either side of Nilgiri plateau indicates uplift of the plateau due to block faulting with a high density mass at the crustal base. The Bhavani Shear Zone is manifested as a steep southerly dipping plane extending to deeper levels along which alkaline and granite rocks intruded into the top crustal layer. The gravity high over Palghat gap is due to the upwarping of Moho by 1–2 km with the presence of a high density mass at intermediate crustal levels. The gravity low in Periyar plateau is due to the granite emplacement, mid-crustal interface and the thicker crust. The feeble gravity signature across the Achankovil shear characterized by sharp velocity contrast indicates that the shear is not a superficial structure but a crustal scale zone of deformation reaching up to mid-crustal level.     

面向地震灾害场景建模的三维地形交互改造技术

在虚拟地震灾害场景基础上,提出一种细节可控的三维地形实时改造算法,用于模拟因地震造成灾区地表形态的变化情况。该方法将地形改造的主要任务交由GPU（图形处理器）的pixel shader（像素着色器）完成,在pixel shader中将原始地形高度图的高程数据读取出来,通过设计算法对数据进行改造后输出至一张新的高度图,并用新的高度图替换原始高度图重新绘制一遍场景,以完成地形的实时改造;使用“乒乓”算法和批处理方式对地形改造效率进一步优化;引入Perlin（柏林）噪声增加了地形改造结果的随机扰动性,使改造结果更加逼真和接近实际情况。实验结果表明：该方法能够在地震灾害场景仿真平台中得到很好的应用,运算效率高,能够满足地形实时改造和交互编辑的实际需求。     

均衡重力异常计算方法

本文提出了采用埃利均衡补偿模式计算5ˊ×5ˊ平均均衡重力异常的一种方认。计算是使用5ˊ×5ˊ平均高程值,将A～O带分为近、中、远三个区:近区用1ˊ40〞×1ˊ40〞的柱体,中区用5ˊ×5ˊ的柱体,远区用15ˊ×15ˊ的柱体,分别采用矩形柱体、质线和质点的正演公式计算地形一均衡校正值。从华南某地区的均衡重力异常图可以看出,根据均衡重力异常可以消除由地壳厚度变化而产生的区域场,突出局部异常场。     

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。