Browsing by Author "Nagendra P. Singh"

Now showing 1 - 6 of 6

A computer program to study the effect of transition layer parameters on the Schlumberger apparent resistivity
(1997) M. Banerjee; S.K. Singh; Nagendra P. Singh; T. Lal
A computer program has been developed for the preparation of master curves of Schlumberger apparent resistivity function (qas/q1) versus the various values of half current electrode spacings over a horizontally stratified three-layered earth model having the intermediate interstratum as the transition layer. The interstratum has two types of conductivity variation: one, the linear variation, and second, the exponential variation of conductivity. The substratum has been taken as either highly resistive or conductive. The conductivity of the top layer merges with that of the substratum having a gradual variation of conductivity with depth in transition layer.
Electromagnetic response of an infinite cable over a layered inhomogeneous earth with exponential variation of conductivity
(1996) Nagendra P. Singh; Tarkeshwar Lal
The problem of calculating the electromagnetic (em) field response of an infinite cable over an inhomogeneous earth is formulated for a multi-layer earth model with one of the layers having exponential variation of conductivity with depth. Solutions for the field components are obtained for the three-layer earth models with the intermediate layer possessing above conductivity variation. Computations are performed for the the absolute-amplitude ratio values, for the quasi-static approximations pertaining to geophysical applications. Results showing the effects of variation of transition layer thickness and conductivity contrast between the top and bottom layers are presented as a function of normalised distance (actual distance divided by the skin-depth computed using top layer conductivity). Results depict characteristic em response over inhomogeneous earth models.
Electromagnetic response of horizontal magnetic dipole over inhomogeneous earth model with linear conductivity variation
(Springer Berlin, 1996) Nagendra P. Singh; T. Lal
The problem of calculating the electromagnetic (em) field response of a horizontal magnetic dipole placed over a multi layer earth model with one of the layers having linear variation of conductivity with depth is formulated. Analytical solutions are obtained for the three layer earth model having linear variation of conductivity in the intermediate transition layer, for the case of quasi-static approximation. Computations are performed for the absolute-amplitude ratio, i.e. the ratio of the absolute amplitude of the field component over a multi-layer model and the corresponding component over a homogeneous half space possessing the conductivity of the top layer. The effects of transition layer thickness and conductivity contrast between the top and bottom layers are investigated by computing these ratios as a function of numerical distance. The results depict characteristic dependence of the em response on conductivity inhomogeneity.
Electromagnetic response of horizontal magnetic dipole over inhomogeneous earth model with linear conductivity variation
(Terra Scientific Publishing Company, 1996) Nagendra P. Singh; T. Lal
The problem of calculating the electromagnetic (em) field response of a horizontal magnetic dipole placed over a multi layer earth model with one of the layers having linear variation of conductivity with depth is formulated. Analytical solutions are obtained for the three layer earth model having linear variation of conductivity in the intermediate transition layer, for the case of quasi-static approximation. Computations are performed for the absolute-amplitude ratio, i.e. the ratio of the absolute amplitude of the field component over a multi-layer model and the corresponding component over a homogeneous half space possessing the conductivity of the top layer. The effects of transition layer thickness and conductivity contrast between the top and bottom layers are investigated by computing these ratios as a function of numerical distance. The results depict characteristic dependence of the em response on conductivity inhomogeneity.
Horizontal magnetic dipole over an inhomogeneous earth model with exponential variation of conductivity
(Birkhäuser-Verlag, 1995) Nagendra P. Singh; T. Lal
The paper outlines the formulation of the problem of calculating the electromagnetic field components due to a horizontal magnetic dipole placed over a multilayered earth model with one of the layers having exponential variation of conductivity with depth. Analytical solutions and numerical computations are performed for three-layered earth models possessing the described conductivity variation in the transition layer. It is assumed that the conduction currents dominate the displacement currents. Results presented here show the influence of the transition layer thickness and the conductivity contrast between the top and the bottom layers on electric and magnetic field components. The results show a characteristic dependence on the conductivity inhomogeneity. © 1995 Birkhäuser Verlag.
MEM analysis of geomagnetic field variations over Narssarssuaq
(Birkhauser Verlag AG, 1997) M. Banerjee; M.K. Singh; Nagendra P. Singh; T. Lal
Maximum entropy spectral analysis (MESA) has been applied to 24 series of hourly daily data and only one daily mean series for the horizontal (H) and vertical (Z) components of the geomagnetic field for the year 1983 as observed at Narssarssuaq, Greenland (71.2°N, 36.7°E) (gm coordinate). The method has isolated some prominent medium frequency signal components. The maximum peaks for H are at 06 hr (0.174 cycles per day (cpd), 3.2 × 104 db) and 08 hr (0.09 cpd, 3.5 × 104 db). Similarly, the maximum peak in Z is observed at 04 hr (0.114 cpd. 5.7 × 104 db). The spectral results for the daily-mean data indicate penods are greater than two days, with 178.5 days (nearly semiannual) being common to both H and Z. Other harmonics have been found for all the series of H and Z components which are mainly caused by the "Effective Period", i.e., the period produced by the combined effect of the sunspot numbers and the sun's rotation period. Such frequencies correspond very well with those found in the geomagnetic indices Ap, Cp and AE. This suggests that the disturbance transient variations are caused by viscous interaction of the solar energies emanating from sunspot regions with the outermost magnetospheric boundary which, in turn, influences the magnetosphere-ionosphere coupling and produces the medium intensity long-duration continuous auroral activities (MILDCAAs) over high latitude regions. Thus, the higher latitude geomagnetic activities are nothing but the "effective period driven MILDCAAs" having a recurrence tendency of 27/n, where n is an integer.