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1.
Magnetotelluric investigations have been carried out in the Garhwal Himalayan corridor to delineate the electrical structure
of the crust along a profile extending from Indo-Gangetic Plain to Higher Himalayan region in Uttarakhand, India. The profile
passing through major Himalayan thrusts: Himalayan Frontal Thrust (HFF), Main Boundary Thrust (MBT) and Main Central Thrust
(MCT), is nearly perpendicular to the regional geological strike. Data processing and impedance analysis indicate that out
of 44 stations MT data recorded, only 27 stations data show in general, the validity of 2D assumption. The average geoelectric
strike, N70°W, was estimated for the profile using tensor decomposition. 2D smooth geoelectrical model has been presented,
which provides the electrical image of the shallow and deeper crustal structure. The major features of the model are (i) a low resistivity (<50Ωm), shallow feature interpreted as sediments of Siwalik and Indo-Gangetic Plain, (ii) highly resistive (> 1000Ωm) zone below the sediments at a depth of 6 km, interpreted as the top surface of the Indian plate,
(iii) a low resistivity (< 10Ωm) below the depth of 6 km near MCT zone coincides with the intense micro-seismic activity in the
region. The zone is interpreted as the partial melting or fluid phase at mid crustal depth. Sensitivity test indicates that
the major features of the geoelectrical model are relevant and desired by the MT data. 相似文献
2.
The computation of electromagnetic (EM) fields, for 1-D layered earth model, requires evaluation of Hankel Transform (HT)
of the EM kernel function. The digital filtering is the most widely used technique to evaluate HT integrals. However, it has
some obvious shortcomings. We present an alternative scheme, based on an orthonormal exponential approximation of the kernel
function, for evaluating HT integrals. This approximation of the kernel function was chosen because the analytical solution
of HT of an exponential function is readily available in literature. This expansion reduces the integral to a simple algebraic
sum. The implementation of such a scheme requires that the weights and the exponents of the exponential function be estimated.
The exponents were estimated through a guided search algorithm while the weights were obtained using Marquardt matrix inversion
method. The algorithm was tested on analytical HT pairs available in literature. The results are compared with those obtained
using the digital filtering technique with Anderson filters. The field curves for four types (A-, K-, H-and Q-type) of 3-layer
earth models are generated using the present scheme and compared with the corresponding curves obtained using the Anderson
sc heme. It is concluded that the present scheme is more accurate than the Anderson scheme 相似文献
3.
Dubey Om Prakash Niwas Sri Awasthi A. K. 《Journal of the Indian Society of Remote Sensing》1986,14(1):39-44
Journal of the Indian Society of Remote Sensing - Development activities must be compatible for possibilities and limitation of natural environment and resources. Predevelopmental analysis must... 相似文献
4.
The paper presents a fast automatic approach to solve the inverse resistivity problem, assisted by optimization, which is a non-linear model-fitting technique. The selected inverse problems are ill-posed and the inverse solution is defined by ‘best fit’ in the sense of least-squares. Formulations are presented in a systematic manner for Newton’s method, least squares method and Marquardt’s modification (ridge regression) method based on local linearization of non-linear problem. The convergence of least-squares method and Marquardt’s method, to provide a robust solution, are first tested on a theoretical model and effectiveness of Marquardt’s method is demonstrated, and then two-field apparent resistivity curves from Banda district, India are interpreted and discussed. 相似文献
5.
The root cause of the instability problem of the least-squares (LS) solution of the resistivity inverse problem is the ill-conditioning of the sensitivity matrix. To circumvent this problem a new LS approach has been investigated in this paper. At each iteration, the sensitivity matrix is weighted in multiple ways generating a set of systems of linear equations. By solving each system, several candidate models are obtained. As a consequence, the space of models is explored in a more extensive and effective way resulting in a more robust and stable LS approach to solving the resistivity inverse problem. This new approach is called the multiple reweighted LS method (MRLS). The problems encountered when using the L 1 - or L 2 -norm are discussed and the advantages of working with the MRLS method are highlighted. A five-layer earth model which generates an ill-conditioned matrix due to equivalence is used to generate a synthetic data set for the Schlumberger configuration. The data are randomly corrupted by noise and then inverted by using L 2 , L 1 and the MRLS algorithm. The stabilized solutions, even though blurred, could only be obtained by using a heavy ridge regression parameter in L 2 - and L 1 -norms. On the other hand, the MRLS solution is stable without regression factors and is superior and clearer. For a better appraisal the same initial model was used in all cases. The MRLS algorithm is also demonstrated for a field data set: a stable solution is obtained. 相似文献
6.
7.
The paper presents an efficient finite difference based 2D-inversion algorithm, EM2INV, for geoelectromagnetic data. The special
features of the algorithm are
The algorithm is tested rigorously by setting up exercises of diverse nature and of practical significance. The stability
of the algorithm is established by inverting the synthetic response corrupted with Gaussian noise. The inversion experiments
are aimed at studying
It has been observed that the Magneto-telluric data deciphers better the vertical position of the target and Geomagnetic Depth
Sounding data deciphers the horizontal variations in a better way. The conductive and resistive bodies are better resolved
by inversion of E- and B-polarization data respectively. The results of multi-frequency inversion imply that the increase
in the number of frequencies does not necessarily enhance the inversion quality especially when the spread of observation
points is sufficiently large to sense the target. The study of a minimum number of observation points highlights the importance
of single point inversion that furnishes useful information about the inhomogeneity. 相似文献
| – | • optimal grid generation based on grid design thumb rules, |
| – | • finite domain boundary conditions, |
| – | • interpolation matrix that permits generation of response at observation points different from grid points, |
| – | • Gaussian elimination forward matrix solver, that enables reuse of already decomposed coefficient matrix, |
| – | • super-block notion that reduces the number of blocks with unknown resistivities and, in turn, the size of Jacobian matrix and |
| – | • bi-conjugate gradient matrix solver for inverse problem which circumvents the need of explicit Jacobian matrix computation. |
| – | • relative performance of response functions, |
| – | • inversion quality of E- and B-polarization data, |
| – | • efficacy of single and multi-frequency data inversion, |
| – | • minimum number of frequencies and observation points needed for successful data inversion. |
8.
Aquifer parameter estimation from surface resistivity data 总被引：7，自引：0，他引：7
This paper is devoted to the additional use, other than ground water exploration, of surface geoelectrical sounding data for aquifer hydraulic parameter estimation. In a mesoscopic framework, approximated analytical equations are developed separately for saline and for fresh water saturations. A few existing useful aquifer models, both for clean and shaley sandstones, are discussed in terms of their electrical and hydraulic effects, along with the linkage between the two. These equations are derived for insight and physical understanding of the phenomenon. In a macroscopic scale, a general aquifer model is proposed and analytical relations are derived for meaningful estimation, with a higher level of confidence, of hydraulic parameter from electrical parameters. The physical reasons for two different equations at the macroscopic level are explicitly explained to avoid confusion. Numerical examples from existing literature are reproduced to buttress our viewpoint. 相似文献
9.
Mahender Singh Ram Niwas M. L. Khichar Manoj K. Yadav 《Journal of the Indian Society of Remote Sensing》2006,34(1):1-5
Field experiments were conducted during 1998–99 and 1999–2000 at research farm of the Department of Agricultural Meteorology,
CCS Haryana Agricultural University, Hisar. Five wheat cultivars: WH 542, PBW 343, UP 2338, Raj 3765 and Sonak were sown on
25th November, 10th and 25th December with four nitrogen levels viz., no nitrogen. 50, 100 and 150% of recommended dose. Leaf area index, dry matter at
anthesis, final dry biomass and grain yield were recorded in all the treatments. Chlorophyll and wax contents of wheat leaves
were estimated at different growth stages. Multiband spectral reflectance was measured using hand-held radiometer. Spectral
indices such as simple ratio, normalized difference, transformed vegetation index, perpendicular vegetation index and greenness
index were computed using the multiband spectral data. Values of all the spectral indices were maximum in 25 November sown
crop with maximum dose of nitrogen (180 kg N ha-1). PBW 343 showed higher values of all the spectral indices in comparison with other cultivars. The spectral indices recorded
during maximum leaf area index stage were correlated with crop parameters. Using stepwise regression, empirical models for
chlorophyll, leaf area index, dry biomass and yield prediction were developed. The ’R2’ values of these models ranged between 0.87 and 0.95. 相似文献
10.
It is proposed that the Straightforward Inversion Scheme (SIS) developed by the authors for 1D inversion of resistivity sounding and magneto-telluric sounding data can also be used in similar fashion for time-domain induced polarization sounding data. The necessary formulations based on dynamic dipole theory are presented. It is shown that by using induced polarization potential, measured at the instant when steady state current is switched off, an equation can be developed for apparent ‘chargeability–resistivity’ which is similar to the one for apparent resistivity. The two data sets of apparent resistivity and apparent chargeability–resistivity can be inverted in a combined manner, using SIS for a common uniform thickness layer earth model to estimate the respective subsurface distributions of resistivity and chargeability–resistivity. The quotient of the two profiles will give the sought after chargeability profile. A brief outline of SIS is provided for completeness. Three theoretical models are included to confirm the efficacy of SIS software by inverting only the synthetic resistivity sounding data. Then one synthetic data set based on a geological model and three field data sets (combination of resistivity and IP soundings) from diverse geological and geographical regions are included as validation of the proposal. It is hoped that the proposed scheme would complement the resistivity interpretation with special reference to shaly sand formations. 相似文献