共查询到20条相似文献，搜索用时 31 毫秒
1.
Mohamed Sharif Berguig Mohamed Hamoudi Jean Louis Lemouël Yves Cohen 《Arabian Journal of Geosciences》2013,6(4):1063-1072
In this work, we report a global mapping of vector lunar magnetic field based on new method of separation of internal and external fields. The magnetic measurements collected during the lifetime of lunar prospector (LP) extended mission during 1999 were strongly disturbed by the solar wind, a period which coincided with a maximum of the 23 cycle activity. The multiscale wavelength external fields were analyzed using spherical harmonic transform. The external field determined by inversion was then removed from each magnetic field component for each half orbit. To map the vector magnetic crustal anomalies, all LP magnetometer data collected at low altitudes in the three different lunar environments: (1) geomagnetic tail, (2) solar wind, and (3) geomagnetic sheath were processed using this new approach. The results obtained using these selection criteria allow us to get a global coverage of the lunar surface by the vector magnetic field at variable spacecraft low altitudes. To validate our mapping, we have developed and applied a method based on properties of potential fields functions. This method can be used to determine both horizontal north and east components using only vertical component. The validated lunar internal magnetic measurements obtained at variable spacecraft altitudes were then continued to a common altitude of 30 km using an inverse method. This mapping confirms firstly the nature of the crustal sources of lunar magnetic field and clearly shows that the strongest concentrations of anomalies are associated with high albedo and/or located antipodal to large young basins (Orientale, Serenitatis, Imbrium, and Crisium) of age about 3.9 Ga. 相似文献
2.
在研究磁异常时,习惯将正常地磁场从测得的地磁场值中消除,以便突出上地幔和地壳内的各种磁异常。正常地磁场的选择正确与否,直接影响到人们对磁异常的认识及地质现象的研究。对于大面积的航空磁测编图,正常地磁场的选择尤为重要。 相似文献
3.
Electrical conductivity structure of the Earth’s deep interior has been successfully mapped out down to approximately 1500 km around the geomagnetic dip equatorial regions of Africa using solar quiet-day ionospheric currents. Spherical harmonic analysis (SHA) was employed in separating the internal and external field contributions to the solar quiet variations. Transfer function was used for each of the external and internal pairs to compute the conductivity-depth profile for the region. Calculated average electrical conductivity values were evidently higher than obtained in other parts of the world farther away from the geomagnetic equator. Sq current vortex foci are observed very close to the geomagnetic equator. Depth of penetration was greatly enhanced. Stations on latitudes less than 1° from the geomagnetic equator show higher electrical conductivity when compared with that situated more than 4° away from it at various corresponding depths. Evidence of discontinuities in the earth layers were also noted at some depths. Highly conductive layers were delineated around 400 km depth and beyond 1200 km. 相似文献
4.
Tectonomagnetic study in the seismoactive area of Narmada-Son lineament,central India: Preliminary results on repeat field observations 总被引：1，自引：0，他引：1
S. Y. Waghmare S. D. Pimprikar P. B. Gawali L. Carlo A. G. Patil 《Journal of Earth System Science》2009,118(3):261-272
Repeated measurements of the total geomagnetic field on the five profiles have revealed a picture of stress-induced tectonomagnetic
effect in the form of secular variation of the total geomagnetic field in the tectonically and seismically active area of
Jabalpur and adjoining areas of the Narmada-Son lineament (NSL), central India. For this experiment, a reference base station
was established within the study area at Jabalpur. Using proton precession magnetometers with a sensitivity of 0.1 nT, simultaneous
measurements of total geomagnetic field were made annually at the base and all field stations. Five cycles of repeated observations
have been performed between 2003 and 2007. For data analysis, a difference method has been applied and the residuals have
been calculated as secular variations of the total geomagnetic field with values ranging from ±0.1nT to about ±14.6nT/yr over
the different stations. The anomalies in secular variation of the total geomagnetic field may be related to anomalous accumulation
of tectonic stresses and tensions on the deep fault zones and crustal blocks due to recent geodynamic processes and active
geological inhomogeneities in the NSL. 相似文献
5.
《Russian Geology and Geophysics》2014,55(7):854-863
The position of lithospheric magnetic anomalies, detected in total magnetic intensity and the vertical component of the magnetic field, has been determined for Siberia using data from the CHAMP satellite. The paper describes the technique for the satellite data processing and the ways of recognition of regional lithospheric magnetic anomalies from satellite-measured values of the total geomagnetic field, which are obtained from several sources (external and internal with respect to the Earth’s surface). Maps of magnetic-field anomalies of different scales have been constructed for several regions of Siberia depending on the method of areal averaging. The possible geologic and physical nature of the magnetic anomalies and their relationship with deep-seated crustal structures are considered. Preliminary interpretation of the magnetic-field maps shows that the anomalies are connected with the present-day large geologic and geophysical elements of the basement. The features of the lithospheric magnetic field, as a parameter reflecting the present position of tectonic structures and their physical properties, can be used for their contouring in combination with other geological and geophysical methods. 相似文献
6.
The Earth’s free oscillations are recorded for the first time in variations of the geomagnetic field measured at the Earth’s surface. The Earth’s free oscillations in the frequency range from 0.3 to 4 mHz manifest in the spectra of geomagnetic variations in the form of clearly expressed quasi-harmonic peaks. It is shown that the spectral amplitudes of the main modes of the Earth’s free oscillations are not constant and change with a periodicity corresponding to a lunar (sideral) month. The data obtained indicate the influence of oscillations in the internal geospheres on variations in the terrestrial magnetic field. The results provide new opportunities to study the Earth’s free oscillations and to specify their multiplet components. In addition, they also have certain implications for further research into the internal structure of the Earth and geodynamic processes in internal geospheres, on the basis of magnetometric data. 相似文献
7.
《Russian Geology and Geophysics》2014,55(10):1229-1238
Phase change of dielectric magnesiowustite in the lower mantle may leave signatures in geomagnetic records of the globally distributed array of observatories. The related features appear in EM induction responses of lower mantle, which are studied theoretically. The surface EM field corresponding to a response of the earth with conductivity anisotropy in a mantle spherical layer is presented as the sum of the magnetic and electric modes. Equations for the fields of both modes and their relationship in a weakly anisotropic earth are obtained by the perturbation method. The two field modes are analyzed jointly and separately to characterize the conductivity tensor of the anisotropic lower mantle. The tensor elements corresponding to the tangential components of the field can be estimated from the magnetic mode alone recorded currently by the global network of geomagnetic observatories. For the tensor data to be complete, observatory data on lateral variations of the electric field are required in addition to three-component geomagnetic records. 相似文献
8.
Knowledge of external inducing source field morphology is essential for precise estimation of electromagnetic (EM) induction response. A better characterization of the external source field of magnetospheric origin can be achieved by decomposing it into outer and inner magnetospheric contributions, which are best represented in Geocentric Solar Magnetospheric (GSM) and Solar Magnetic (SM) reference frames, respectively. Thus we propose a spherical harmonic (SH) model to estimate the outer magnetospheric contribution, following the iterative reweighted least squares approach, using the vector magnetic data of the CHAMP satellite. The data covers almost a complete solar cycle from July 2001 to September 2010, spanning 54,474 orbits. The SH model, developed using orbit-averaged vector magnetic data, reveals the existence of a stable outer magnetospheric contribution of about 7.39 nT. This stable field was removed from the CHAMP data after transforming to SM frame. The residual field in the SM frame acts as a primary source for induction in the Earth. The analysis of this time-series using wavelet transformation showed a dominant 27-day periodicity of the geomagnetic field. Therefore, we calculated the inductive EM C-response function in a least squares sense considering the 27-day period variation as the inducing signal. From the estimated C-response, we have determined that the global depth to the perfect substitute conductor is about 1132 km and its conductivity is around 1.05 S/m. 相似文献
9.
Archaeomagnetic dates derived from geomagnetic field direction records in baked materials are proposed for a mediaeval brick kiln (from inclination I and declination D) and for bricks from a brick wall (from I only) in northern Belgium. They are used to verify whether a brick chronology based on the format of bricks is feasible in Flanders. The brick kiln yielded a highly reliable average magnetization direction corresponding to an archaeomagnetic date around A.D. 1650, using the British and French geomagnetic field secular variation curves as a reference, at least half a century younger than expected from historical data. The fidelity of the geomagnetic records was controlled by measuring the magnetic anisotropy of the bricks. Anisotropy of magnetic susceptibility (AMS) measurements demonstrate that the bricks have a shape related magnetic fabric, which is induced during the molding process. A test to control whether AMS can substitute for the anisotropy of thermo‐remanent magnetization (ATRM) failed because of induced changes during laboratory heating. © 2003 Wiley Periodicals, Inc. 相似文献
10.
地球偶极磁场成因新探讨 总被引：1，自引：0，他引：1
以地球内部结构为立论基础和现代物理学中的引力理论和粒子理论为理论根据,阐明了地球外壳与内核运动的差异性,进而提出了以摩擦起电为主的差速发电机制和地磁场的形成机理,总结出了地球内核旋转轴上任一点的强度计算公式和地磁极性的判别方法,并解释了地磁学中的磁轴问题、磁极漂移和地磁场的极
性转换。 相似文献
性转换。 相似文献
11.
《International Geology Review》2012,54(2):191-195
The author proposes a method of telluric-magnetic mapping, profiling, and exploration. The profiling involves recording of short-period variations in the telluric current and the magnetic field (MTP) and an areal (MVR), similar to the above. The method can be used on any segment of the crust, especially with newly designed, highly sensitive short-period magnetometer. The magnetic fields of telluric currents are measured by means of a four-channel oscillograph controlled from a panel in which switches are incorporated. The magnetic fields of the telluric current are measured at two points, since the automatic switching arrangement permits a procedure identical with the measurements in the telluric current. Amplitudes and periods of almost sinusoidal waves are measures of the chords of the elliposidal electric and magnetic fields. Analysis of magnetic field mapping and its results are given. The author feels that the telluric-magnetic profiling should replace direct telluric voltage measurements in many regions because of its economics. It gives precise data on the structure of the sedimentary cover. Telluric-exploration will open up entirely new possibilities in permafrost zones and the method will be substantially more efficient than direct telluric measurements. — A.W. Bellais 相似文献
12.
通过对陕西耀州窑遗址内4个古窑,临潼兵马俑一号坑,西铜一级公路经过黄堡工地开挖的两个五代窑,以及耀州窑博物馆仓库工地内开挖的一个金代窑和一个春秋窑遗址的古地磁研究,初步得出了西安地区古地磁场变化的规律,为鉴定从春秋到金代西安地区的古遗址、古文物提供了考古地磁学上的一个粗略的标准。 相似文献
13.
《International Geology Review》2012,54(4):624-632
Results of regional geophysical work in the U.S.S.R. allow a measure of correlation between the known structural features of the crust and those of the geomagnetic field. The “normal” magnetic field used for identifying magnetic anomalies is obtained by graphic smoothing of isolines of total intensity T. Detailed analysis of data obtained in aeromagnetic and gravity surveys throughout the U. S. S. R. leads to the conclusion that the cause of the observed regional magnetic and gravity anomalies lies in the same associated geologic objects located at the same level - that of a magnetoactive interval of the crystalline envelope of the earth. The conclusions that can be drawn from existing data are: 1) the existence of “continental” anomalies of the geomagnetic field cannot be explained as an effect of the crust; 2) the basaltic layer does not affect the distribution of the geomagnetic field; 3) the anomalies in the basic (normal) geomagnetic field are caused by the presence of thermomagnetic geologic bodies in the granitic layer; accordingly, it is theoretically possible to determine the thickness of the continental layer from magnetometric data. A table showing correlative depths of the basaltic layer, its thickness, and anomalous magnetic field, as well as magnetic profiles is included.--C. E. Sears. 相似文献
14.
15.
地磁场模型的计算和评述 总被引：1，自引：0，他引：1
评述了计算地磁场区域模型的各种数学方法,如:利用多项式方法可以计算地磁场的Taylor多项式模型和Legendre多项式模型,利用球冠谐和分析方法可以计算出磁场的冠谐模型。本文指出了建立区域模型各种方法的优缺点,指出球冠谐和分析方法是计算地磁场三维模型的好方法。 相似文献
16.
柬埔寨王国位于低纬度地区,地质勘查程度较低,地面高精度磁测技术能够快速获取磁异常信息,进行找矿评价。在低纬度地区磁化方向主要以水平磁化为主,磁性体产生的磁异常以负磁异常为主。本文通过对柬埔寨王国Mesam金矿磁测数据进行倒相180°、化赤和低纬度化极处理对比,认为三种处理方法得到的结果都能够完整地反映磁场分布特点,在不能忽略剩磁影响的低纬度地区对实测数据进行低纬度化极后再进行解释更加贴近真实且细节更加丰富。通过对低纬度化极后的磁异常进行水平总梯度模和小波多尺度分解计算等位场异常处理,认为磁异常水平总梯度模计算能够较好地反映深部地质体的边界范围,小波多尺度分解计算能够提取特定深度地质体的空间信息,在该区选取的磁异常处理技术是有效的,为进一步扩大该金矿区远景储量提供了新的思路。 相似文献
17.
地面磁测数据正常场改正现行方法探讨 总被引：2，自引：0，他引：2
地面磁测数据正常场改正是地面磁测工作资料整理的一个不可或缺的步骤。正常场改正的好与坏、对与错,改正的程度如何,都直接关系到磁异常的形态,以至于磁测工作的解释结果。本文通过讨论国际地磁参考场的求法、地面磁测工作正常场的改正意义,比较了国际地磁参考场与地磁图的精度,对现行的地面磁测数据正常改正的方法探讨后,通过工作实例说明... 相似文献
18.
古地磁学是一门典型的交叉学科,通过综合地质学、地球物理学、环境科学等学科相关方法,分析天然样品中记录的磁学信息,深入研究地磁场演化、地球动力学过程、古环境与古气候演化等.自20世纪中叶以来,古地磁学在各研究领域得到快速发展,通过进一步与其他学科交叉,衍生出诸多新兴方向.首先回顾了古地磁学的发展历史与基础研究领域.在此基础上,重点介绍了高精度卫星磁测与相关研究新领域、月球与火星磁学研究的新进展.同时,对古地磁学与高精度磁测等方法集成在地磁场演化、板块构造、深部结构、月球磁场演化、火星磁场及环境演化等方面的综合应用进行了讨论.最后,对古地磁学未来的潜在研究方向进行了展望. 相似文献
19.
基于我国大陆最新观测所得的1 302个地磁测点和32个地磁台站磁偏角D、磁倾角I、总强度F的1 334组准确数据,并结合地壳磁异常能谱变化特征,对增强地磁模型(EMM2010)在我国大陆的精度及其适用性进行了定量分析。结果表明：EMM2010模型(D、I、F)在我国大陆的总体精度分别为10.45′、8.08′、112.85 nT ;东北、华北与新疆地区模型的精度为13.07′、8.90′、130.89 nT ;华南、青藏高原及其东缘地区模型的精度为7.07′、6.65′、81.84 nT;其精度是受模型有限的截断阶数、各区域的磁异常状况和磁测数据的误差等因素共同影响的。EMM2010模型的精度在我国大陆表现出显著的地域分布特征,与磁异常的分布形态及其复杂程度、梯度密切相关,异常越突出,形态越复杂,模型的精度越低。与世界地磁模型(WMM2010)、第11代国际参考地磁场(IGRF11)相比,EMM2010模型在我国大陆的总体精度平均提高了50%,主要原因是模型不仅包含了地球主磁场,同时还包含了地壳磁场。EMM2010模型应用于我国大陆的实例及精度分析表明,模型具有一定的适用性,但有其局限性,不能准确反映出我国大陆的地磁场信息,鉴于模型的精度,建议在EMM2010模型基础上,结合我国最新的各部门的高精度磁测数据,构建我国高精度的地磁场模型。 相似文献
20.
Robert A. Langel 《Journal of Earth System Science》1990,99(4):581-618
Among the first measurements made from near-Earth orbiting satellites were measurements of the magnetic field. The sources
of that field lie both within the Earth, in its core and crust, and in the surrounding ionosphere and magnetosphere. This
article summarizes some of the methodology and results for studies of the Earth’s mantle and crust. Mantle conductivity studies
can be made either by studying signals impressed on the Earth from outside, e.g., the ionosphere or magnetosphere, or by studying
signals originating in the core and transmitted through the mantle. Crustal field studies begin with a careful selection of
the data and subsequent removal of core and external fields by some sort of filtering. Average maps from different local times
sometimes differ, presumably due to the remaining presence of fields of external origin. Several techniques for further filtering
are discussed. Where large-area aeromagnetic maps are available, crustal maps derived from satellite data can be compared
with upward continued data. In general, the comparisons show agreement, with some differences, particularly in and near the
auroral belts. The satellite data are further reduced by various methods of inverse and forward modelling, sometimes including
reduction to the pole (RTP). These techniques are generally unstable at the equator. Common methods of stabilizing the inversions
include principle components analysis and ridge regression. Because of the presence of the core field, the entire crustal
contribution from the field is not known. Also, there is a basic nonuniqueness to the inverse solutions. Nevertheless, magnetizations
that are interpretable can be derived. 相似文献