Chebyshev低通滤波器在位场数据波数域导数换算中的应用

导数换算作为常用的位场数据处理手段具有重要的物理意义。由于实际测量误差和噪声的影响,波数域导数换算存在计算过程不稳定、求导结果精度差的问题。为了降低噪声干扰,提高导数计算精度,提出了在波数域常规导数算子基础上附加Chebyshev低通滤波器的任意阶导数换算方法。通过分析该滤波器的滤波特性,并结合位场异常径向平均功率谱曲线特征,确定了Chebyshev低通滤波法的滤波参数,减少了人为因素对求导结果的干扰。二度体和三度体模型试验表明,与其他3种方法(常规FFT(fast Fourier transformation)法、向上延拓法和ISVD(integrated second vertical derivative)法)相比,该方法计算的导数与理论值的均方根误差最小,求导结果精度较高。在虎林盆地布格重力异常数据处理中,利用该方法计算的垂向二阶导数受噪声干扰小,结果可靠性较高,依此划分出的8条大断裂和11条小断裂在以往研究中均得到证实。     

最佳向上延拓高度的估计

提出根据两个相邻高度重力异常向上延拓值相关系数与高度的关系 ,以估计应用向上延拓分离区域及剩余重力异常的最佳向上延拓高度的方法。二维模型计算表明 ,不同高度的观测重力异常向上延拓值和观测面上区域重力异常值的互相关系数与高度的关系曲线 ,存在一个明显的极大值 ;这个极大值对应的高度 ,就是从观测异常中分离出这一区域重力异常所需要的最佳向上延拓高度。两个相邻高度重力异常向上延拓值之间的互相关系数与高度的关系曲线 ,存在一个明显的转折点 ,这个转折点对应的高度 ,就是所求的最佳向上延拓高度。应用本方法处理华南北部地区布格重力异常的结果表明 ,由于引起本区区域重力异常的地质因素 ,除了莫霍面及上地壳底面外 ,还受到本区广泛分布甚至出露的花岗岩的影响 ;所以为了从观测异常中分离这一区域异常所需要的最佳向上延拓高度为 2 0 0km ,小于莫霍面及上地壳底界面的平均深度。为了从观测异常中分离出由莫霍面引起的重力异常所需要的向上延拓高度 ,达到 15 0km。因此 ,应用本方法处理实测重力资料 ,必须首先了解引起区域重力异常的场源情况。     

航空重力数据的等波纹FIR低通滤波试验

为解决航空重力测量中的核心技术之一——强噪声背景下提取微弱重力异常信号的问题,根据等波纹切比雪夫逼近理论,采用瑞米兹（Remez）交换算法设计等波纹线性相位FIR低通滤波器,利用模型数据对该方法进行了验证,并通过GT-1A型航空重力系统测量数据进行滤波试验。结果表明,基于Remez交换算法设计等波纹线性相位FIR低通滤波器,在自由空气重力异常获取的滤波试验中,能获得与GT-1A系统卡尔曼平滑滤波相同的效果。     

Contribution de la gravimétrie à l'étude de la structure du bassin de Tadla (Maroc) : Implications hydrogéologiques

This study is based on the analysis and the interpretation of the gravity data of the Tadla basin. Its purpose is to increase the knowledge of this basin structure. A residual anomaly map was first calculated from the Bouguer anomaly data witch are strongly affected by a regional gradient. The computed map provides information on the ground density variation but it does not bring enough of new elements. Data filtering allows us to emphasize the structures affecting the basin. We chose the horizontal gradient coupled to the upward continuation techniques that permit to highlight news structures and to give information on their dip. The elaborated structural map of the study area constitutes a useful document for rationalizing the future groundwater exploration in the Tadla basin. To cite this article: A. Najine et al., C. R. Geoscience 338 (2006).     

中国南海卫星重力数据Butterworth滤波处理

通过对重力模型数据进行Butterworth滤波处理,发现该方法对高频噪声具有很好的滤波效果。对Geosat和ERS—1卫星提供的重力数据进行了网格化和Butterworth滤波处理,得到中国南海自由空气重力异常值为-42~89 m Gal。经与GRACE卫星提供的数据进行比较,发现该方法得到的结果具有更好的精度和分辨率。     

全张量重力数据水平分量噪声滤除方法

为获得更好的噪声滤除方法,本文建立一个球状模型,对全张量重力梯度三个水平分量加入高斯白噪声,并利用FFT和PSD分别对加噪后三个分量(Vxx1,Vxy1,Vyy1)进行频谱分析,根据频谱分析结果分别设计了巴特沃斯低通滤波器和高斯低通滤波器对加噪数据进行滤波,取得了较好效果,并利用复杂模型验证滤波效果。     

基于航空重磁资料对大杨树盆地南部及周边岩浆岩分布规律的认识

基于区域地质-地球物理综合研究, 利用最新实测的航空重磁综合测量数据, 结合野外踏勘与物性测量结果, 采用化极、向上延拓、垂向导数等场源分离或异常提取技术, 研究了大杨树盆地南部及周边不同类型岩浆岩的重磁异常响应, 圈定了其空间分布范围, 揭示了区域岩浆岩发育特征、分布规律及其控制因素。研究表明, 研究区不同类型的岩浆岩具有迥然不同的航磁异常特征; 本次采用的突出局部重磁异常的地球物理方法可以有效识别酸性、中酸性、中基性等岩浆岩; 本次系统圈定了具有地质意义的岩浆岩百余处, 多数岩浆岩沿北东向与北西向断裂及其两侧分布, 尤以断裂交汇部位最为发育, 说明断裂对岩浆活动具有明显的控制作用; 航空重磁揭示研究区发育较大规模的隐伏中基性火山岩, 为区域基础地质研究和火山岩盆地油气藏资源评价提供了重要的地质-地球物理依据。     

重磁场联合反演技术在庐纵盆地基底构造解释中的应用

安徽庐枞地区位于怀宁庐江“磁高重高”一级异常带的枞阳--庐江次级异常区.采用重磁场联合反演技术的多层面边缘检测方法(WORMS法)对庐枞地区多层面边缘进行检测,得到了地下不同深度的密度或磁性信息以及重、磁异常边界.根据上延层高度布格重力异常,结合航磁区域和局部异常分布特点,进行了断裂构造的推断与基底隆起区的划分,再利用空间分析技术对这些圈闭区域进行相交计算,划分出重磁同高、重低磁高、重高磁低、重磁同低等4种组合空域,提出庐枞盆地磁性基底为“一隆两凹”形态(庐枞盆地基底界面三维结构图)的新认识.     

The crustal structure of the Sahel Basin (eastern Tunisia) determined from gravity and geothermal gradients: implications for petroleum exploration

An analysis of Bouguer gravity anomaly data and geothermal gradient data obtained from bottom hole and drill stem tests temperature is used to determine the crustal structure of the Sahel Basin in eastern Tunisia and its role in the maturation and location of the large number of oil and gas fields in the region. The regional Bouguer gravity anomaly field is dominated by gradual increase in values from the northwest to southeast and is may be caused by crustal thinning as revealed by regional seismic studies. In addition, higher geothermal gradients in the same region as the Bouguer gravity anomaly maximum add an additional constraint for the existence of crustal thinning in the region. A detailed analysis of the Bouguer gravity anomaly data was performed by both upward continuation and horizontal gradients. These two techniques were combined to show that the study area consists of two structural regions: (1) the North–South Axis (NOSA)–Zeramedine region which is characterized by northwest-dipping, northeast-striking faults, thicker crust (30–31 km) and low geothermal gradients, and (2) the Mahres–Kerkennah region which is characterized by vertical, northwest-striking faults, thinner crust (28–29 km) and higher geothermal gradients. The correlation of a variety of features includes mapped and geophysically defined faults, volcanic rocks, a thinned crust and high geothermal gradients within the same location as known oil and gas fields indicate that the faults are a major factor in the location of these petroleum accumulations.     

基于位场分离方法的极地冰盖重力异常剥离：以模型试验为例

为了提高极地重力数据处理的质量,降低巨厚冰层对重力数据解释的影响,将极地大陆冰盖引起的重力异常从叠加异常中剥离出来成为极地重力数据处理的重要步骤之一。针对该问题,本文建立两个极地大陆冰层构造模型,对不同模型进行正演获得对应布格重力异常,再尝试利用三种位场分离方法,包括趋势分析法、向上延拓法和优化滤波法,对冰层引起的重力异常进行剥离试验,基于模型试验结果对比分析不同位场分离方法对极地冰层重力效应剥离的应用效果。模型试验结果显示,趋势分析法在冰层界面起伏较平缓情况下效果较好,但当冰层界面起伏复杂时难以用数学表达式精确拟合区域场,因此易在结果中引入虚假异常;向上延拓法在局部场源较浅的异常分离中效果较好,但由于极地模型冰盖深度较深及延拓高度选取不合理,在试验中出现了分离不足的情况;优化滤波法在相对复杂模型中分离效果相对好,但由于频段选取的主观性,使得该方法也易出现分离不足或过度情况。综合上述模型试验表明,在剥离极地冰盖引起的重力异常时,由于极地冰盖厚度起伏等地质情况复杂多变,应结合实际地质情况及其他可获得的地球物理资料进行综合分析,选择适用于具体情况的分离方法。     

Assessment of subsurface structural elements around greater Cairo by using integrated geophysical tools

Geophysical techniques such as gravity, magnetic and seismology are perfect tools for detecting subsurface structures of local, regional as well as of global scales. The study of the earthquake records can be used for differentiating the active and non-active fault elements. In the current study, more than 2,200 land magnetic stations have been measured using two proton magnetometers. The data are corrected for diurnal variations and then reduced by the International Geomagnetic Reference Field. The corrected data have been interpreted by different techniques after filtering the data to separate shallow sources (basaltic sheet) from the deep sources (basement complex). Both Euler deconvolution and 3-D magnetic modeling were carried out. The results of interpretation indicate that the depth to the upper surface of basaltic sheet ranges from <10 to 600 m, depth to the lower surface ranges from 60 to 750 m, while the thickness of the basaltic sheet varies from <10 to 450 m. Moreover, gravity measurements are conducted at 2,250 stations using a CG-3 gravimeter. The measured values are corrected to construct a Bouger anomaly map. The least squares technique is then applied for regional–residual separation. The third order of least squares is found to be the most suitable to separate the residual anomalies from the regional one. The resultant third-order residual gravity map is used to delineate the structural fault systems of different characteristic trends. The trends show an NW–SE trend parallel to that of Gulf of Suez, an NE–SW trend parallel to the Gulf of Aqaba and an E–W trend parallel to that of the Mediterranean Sea. Taking seismological records into consideration, it is found that most of the 24 earthquake events recorded in the study area are located on fault elements. This gives an indication that the delineated fault elements are active.     

中国视密度图与大地构造单元

提出根据区域重力异常计算地壳表层视密度分布的方法。依据原观测平面异常与延拓到某一高度平面异常的差值场所具有的突出浅源异常、压制深源异常的特点 ,按维纳滤波原理 ,应用多层格林等效层模型精确模拟该差值重力场的径向对数功率谱 ,设计重力场在频率域进行异常分离的具有自适应性的优选延拓算子 ,实现垂向异常分离。利用重力场可看成由许多等效直立棱柱体叠加的原理 ,在频率域内 ,通过换算重力场的一次导数 ,计算出视密度的分布。用上述方法处理中国布格重力异常图 ,获得了中国地壳表层 0 10km剩余重力异常 ,并成功编制视密度图。比较表明 ,视密度的分布特征与大地构造单元及分区有较好的对应关系。地壳表层的岩石密度分布的获得 ,为中国的基础地质与构造研究提供了重要依据。     

用解析延拓求取剩余磁异常来圈定浅部隐伏磁铁矿脉

剩余磁异常求取是一种对磁场强度进行化极,解析延拓后提取浅部磁性介质异常的高通滤波方法。对于处于强磁性围岩的磁铁矿脉来说,浅部磁铁矿脉的异常往往被大规模的磁性围岩所引起的异常所掩盖。磁场强度与场源到测点距离的平方(二度体)或者立方(三度体)成反比,进行向上延拓的时候,由浅部场源引起的高频异常衰减快,深部场源引起的低频异常衰减的慢,因此地面实测磁场去掉向上解析延拓后的磁场值,可突出反映近地表磁性体引起的高频异常。这里通过解析延拓求取剩余异常,实现浅部磁铁矿脉异常信息的提取,为寻找隐伏的磁铁矿脉提供依据。并且利用此方法在秘鲁共和国Morritos铁矿圈定隐伏磁铁矿脉,验证了剩余异常在大规模的高磁性围岩中寻找隐伏磁铁矿脉的应用效果。     

维纳滤波技术及其在新疆地区重力场划分中的应用

基于维纳滤波原理,应用多层格林等效层模型模拟实测重力场的径向对数功率谱,采用改进的格拉姆-施密特正交化方法计算功率谱密度函数,确保了数值的稳定性,得到了较为满意的结果。通过理论模型实验,证实了利用维纳滤波方法提取深部场时可以保证低频成分不衰减的功能,能够较为精确地提取区域异常,从而实现频率域中位场的分离。运用维纳滤波方法对新疆地区布格重力异常进行了分离处理,获得了基于最佳滤波原理计算的新疆地区区域重力异常,并根据新疆地区布格异常和区域场特征,划分了9条深大断裂和5个一级构造单元。     

优选延拓技术及其在中国布格重力异常图处理上的应用

从维纳滤波原理出发 ,应用多层格林等效层模型精确模拟实测重磁场的径向对数功率谱 ,实现了重磁场在频率域的优选延拓。通过理论模型实验 ,证实了优选延拓算子具有向上延拓时不过分衰减低频信号、向下延拓时不过分突出或压制高频信号的选择性功能。根据优选向上延拓可以保证低频成分不衰减的性质 ,能够较为精确地提取区域异常 ,进而分离出局部异常。利用优选向下延拓可以对指定波段放大 ,而对其他波段保持全通的特征可以实现对某一深度或尺度的局部异常有选择地增强。运用优选延拓技术对中国大陆布格重力异常进行了增强与分离处理 ,获得了基于最佳滤波原理计算的中国大陆区域重力异常、剩余重力异常和带通重力异常。为研究中国大陆表层的岩石物性结构及平面分布特征提供了新的资料 ,同时也说明了优选延拓技术具有广阔的应用领域     

额尔古纳地块中生代火山岩盆地基底构造特征:来自灵泉盆地的启示

灵泉盆地布格重力异常特征表明灵泉盆地两侧重力低异常区主要为侏罗-白垩系断陷区,中部主要为基底隆起区.对布格重力异常进行向上延拓处理,结果发现深部地质体具有"东、西深,中间浅"分布特征;剩余重力异常也说明中部局部重力高主要反映基底隆起,东部和西部局部重力低主要反映侏罗-白垩系断陷.灵泉盆地基底断裂早期以北东向为主,晚期发育北西向断裂,区内还有早期近南北向和东西向断裂存在.将灵泉盆地构造单元划分为西部断陷区、中部隆起区和东部断陷区之后发现,灵泉盆地实际上是个相对隆起而不是断陷盆地,这是盆地发生构造反转作用的结果,额尔古纳地块上的其他中生代火山岩盆地普遍具有这种模式,额尔古纳地块中生代盆地基底总体上具有"南深北浅"的特点.      

增强弱磁异常信号的HILBERT变换方法

在油气勘探中,与油气相关的磁异常由于其信号非常弱,通常很难从干扰中分离出来,可以证明希尔伯特变换滤波方法增强弱磁异常是一种有效方法,广东三水盆地的剖面处理解释说明了这一点。     

A New Approach to Gravity Anomaly Separation: Differential Markov Random Field (DMRF)

In this paper the authors introduce a novel approach to stochastic image processing, denoted as Differential Markov Random Field (DMRF), which has been applied to gravity anomaly separation problems. The advantages of the method are that it introduces only little distortion into the shape of the original image and that it is not affected significantly by factors such as the overlap power spectra of regional and residual fields. Testing of the proposed meth using synthetic examples gave excellent results.     

Chebyshev逼近滤波器在位场分离中的应用

在对经典FIR数字滤波器的设计方法进行研究的基础上,提出了一种可以用于位场分离的基于Chebyshev最佳一致逼近原理的FIR滤波器的设计方法。在理论模型实验中,采用基于Hanning窗的低通滤波器计算出的区域异常最大误差为6.266×10^-6 m/s² ,均方差为2.115×10^-6 m/s² ,最大百分比误差为22.2%,而且计算点在±9 km以外的误差均大于10.1%。而利用最佳一致逼近原理分离出的区域场和局部场与理论异常值拟合得较好,曲线基本重合。分离出的区域异常最大误差为3.101×10^-6 m/s² ,均方差为0.989×10^-6 m/s² ,最大百分比误差仅在边部的几个数据上,为7.76%,其余各点的误差均小于4.1%。实例检验中将该方法用于孙吴—嘉荫剖面布格重力异常场的分离,分离出的区域场中局部场残留少,分离彻底,效果较为理想。     

Spatial filtering of exploration geochemical data using EDA and robust statistics

The spatial filtering techniques that are used for the analysis and interpretation of exploration geochemical data to define regional distribution patterns or to outline anomalous areas are, in most cases, based on non-robust statistical methods. The performance of these techniques is heavily influenced by the presence of outliers that commonly exist in the data. This study describes a number of filtering techniques motivated by the development of exploratory data analysis (EDA) and robust statistical procedures. These are the median filter (MF) and the adaptive trimmed mean filter (ATM) for the smoothing of regional geochemical data to reduce spurious variations; two new filters, the fence filter (FF) and the notch filter (NF), have been developed to define geochemical anomalies.The application of the spatial filtering techniques is illustrated by Zn data from approximately 3100 stream sediment samples taken in a regional geochemical survey over 25,000 km² of the western margin of the São Francisco Basin, Brazil. Regional distribution patterns for Zn obtained by the MF and ATM filters are clearly related to known stratigraphic units. Anomaly filtering using the FF and NF has delineated most known base metal and gold occurrences, as well as a number of anomalies located in geologically favourable environments but unrelated to any known mineralization. The two anomaly filters have, for the most part, defined the same anomalies in the study area but only the NF highlights the anomaly associated with the important Morro Agudo Pb-Zn deposit, which is too subtle to be immediately apparent in the unprocessed data.