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71.
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R. Nagendra I. B. Ramaprasada Rao Satyanarayan Kabra 《Journal of Earth System Science》1985,94(3):269-277
The transient electromagnetic response due to a pair of horizontal conducting sheets induced by a loop field is obtained.
The response characteristics in the three different regions (above the upper sheet, between the two sheets and below the lower
sheet) are briefly discussed.
In the first and second regions the composite response is characterised by an overburden response asymptote during early times
and a target response asymptote during late times. The transition zones are characterised by shoulder-like bends. In the third
region, the composite response increases in direct proportion to the induction number, eventually merging with the target
response for large values of the induction number. 相似文献
74.
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76.
Alan P. Carr 《地球表面变化过程与地形》1983,8(3):293-296
The method described involves the use of an electro-optical distance measurer mounted on a theodolite. Observations are taken onto a series of acrylic reflectors, aligned at right angles to the line of sight, and slope distances and vertical and horizontal angles are recorded. From these data it is possible to obtain surface heights to an accuracy of ±0·5 cm at 200 m and to avoid any direct disturbance of the site under investigation. 相似文献
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Whole mantle SH velocity model constrained by waveform inversion based on three-dimensional Born kernels 总被引:1,自引:0,他引:1
Nozomu Takeuchi 《Geophysical Journal International》2007,169(3):1153-1163
A whole mantle SH velocity model is obtained by using a unique data set and techniques. Body and surface waveforms including major and multi-orbit phases are used as a data set and are inverted by using 3-D Born kernels. The resultant model, SH18CE, reveals the different natures of the two major upwelling systems: the strong low velocity anomalies beneath Africa extend for more than 1000 km from the core–mantle boundary (CMB), whereas those beneath the Pacific are restricted to 300–400 km from the CMB. The results also show the variable natures of stagnant slabs on the 670 discontinuity around Japan: the depths of the strongest high velocity anomalies within the stagnant slabs are different region by region, which is consistent with the detailed delay time tomography model in this area. 相似文献
79.
The time-domain EM induction response of non-magnetic and magnetic targets can be approximated using a conductive permeable prism composed of six faces of conductive plates, each face being composed of a set of conductive ribbons. The effect of magnetic permeability is included by the use of two “apparent flux gathering” coefficients, and two “effective magnetic permeability” coefficients, in the axial and transverse directions. These four magnetic property coefficients are a function of physical properties and geometry of the target, but are independent of prism orientation relative to a transmitter. The approximation algorithm is computationally fast, allowing inversions for target parameters to be achieved in seconds. The model is tested on profiles acquired with a Geonics EM63 time-domain EM metal detector over a non-magnetic copper pipe target, and a steel artillery shell in horizontal and vertical orientations. Results show that this approximation to a permeable prism has a capability of fitting geometric, conductivity and magnetic parameters at both early and late sample times. The magnetic parameters show strong change from early to late times on the EMI decay curve, indicating that the magnetic properties of the target have non-linear characteristics. It is proposed that these magnetic parameters and the nature of their non-linearity may carry additional discrimination information for distinguishing between intact munitions and scrap in UXO studies. 相似文献
80.
F. Shubitidze K. O'Neill B.E. Barrowes I. Shamatava J.P. Fernndez K. Sun K.D. Paulsen 《Journal of Applied Geophysics》2007,61(3-4):292-303
This paper presents an application of the normalized surface magnetic charge (NSMC) model to discriminate objects of interest, such as unexploded ordnance (UXO), from innocuous items in cases when UXO electromagnetic induction (EMI) responses are contaminated by signals from other objects. Over the entire EMI spectrum considered here (tens of Hertz up to several hundreds of kHz), the scattered magnetic field outside the object can be produced mathematically by equivalent magnetic charges. The amplitudes of these charges are determined from measurement data and normalized by the excitation field. The model takes into account the scatterer's heterogeneity and near- and far-field effects. For classification algorithms, the frequency spectrum of the total NSMC is proposed and investigated as a discriminant. The NSMC is combined with the differential evolution (DE) algorithm in a two-step inversion procedure. To illustrate the applicability of the DE–NSMC algorithm, blind test data are processed and analyzed for cases in which signals from nearby objects frequently overlap. The method was highly successful in distinguishing UXO from accompanying clutter. 相似文献