E. Chandrasekhar

Indian Institute of Technology Bombay | IIT Bombay ·  Department of Earth Sciences

Geoelectrical studies have been widely used for characterization of the subsurface features for groundwater exploration, environmental aspects, etc. The present study involves the application of multi-electrode resistivity imaging (MERI) to demarcate potential zones for groundwater exploration. The Wenner-Schlumberger (WS) array has been deployed f...

Geophysical signal processing is an important branch of geophysics that deals with various signals and systems. It serves as a backbone for efficient analysis and interpretation of the complex geophysical data. Concepts of signal processing are encountered at various stages, right from the data acquisition to processing to interpretation. Over the...

Frequency attributes embedded in nonlinear geophysical signals such as well-log data or seismic data can provide vital clues in the effective characterization of the subsurface reservoir. Therefore, it is always important to recognize suitable mathematical techniques that need to be employed to extract such vital information from the nonlinear geop...

In this paper, we investigate the correction of ionospheric amplitude scintillations appearing as image artifacts in low frequency synthetic aperture radar (SAR) data. A method has been proposed to separate amplitude and phase components of fully polarimetric SAR (POLSAR) coherency matrix [T], and then implement a combination of multi-level, two-di...

Fractional Gaussian noise (fGn) provides an important parametric representation for the data recorded from long-memory processes. Also it has been well established in literature that the orthogonal wavelet transforms prove to be the optimal bases to represent the data as fGn or fBm (fractional Brownian motion) models. This paper highlights the stat...

Magnitude cumulants of wavelet transform Multifractal analysis Ionospheric TEC P-model of multiplicative cascades a b s t r a c t Understanding of the spatio-temporal behaviour of nonlinear geophysical signals, such as ionospheric total electron content (TEC) by multifractal analysis brings out the chaotic and intermittent nature of the signal unde...

Time-series modelling forms an important area of research in geophysics. Time-series models can be linear, like linear state-space models or non-linear, like artificial neural networks. One way to judge the goodness of different models associated with a given time-series is to assess the prediction capabilities of these models. Some of the importan...

Geophysical well-log data manifest nonlinear behaviour of their respective physical properties of the subsurface layers as a function of depth. Therefore, nonlinear data analysis techniques must be used to understand and characterize the nature of the subsurface lithologies, vis-a-vis their degree of heterogeneity. One such nonlinear technique is t...

Geophysical well-log data manifest the nonlinear behaviour of their respective physical properties of the heterogeneous subsurface layers as a function of depth. Therefore, nonlinear data analysis techniques must be implemented, to quantify the degree of heterogeneity in the subsurface lithologies. One such nonlinear data adaptive technique is empi...

In 21st century water is the main socioeconomic problem due to increasing demand of fresh water particularly in hard rock terrain. In hard rock terrain groundwater plays the vital role for fresh water exploration. For groundwater exploration the hydrogeological fractures has been mapped in the study area by geological field work. The objective of t...

Geophysical well-log data provide a unique description of the subsurface lithology, as they represent the depositional history of the subsurface formations, vis-à-vis the variation of their physical properties as a function of depth. However, a correct identification of depths to different lithostratigraphic units is possible only by using effectiv...

The spatio-temporal variations in geophysical well-log signals, which often reflect their scale invariant properties, can be well studied with multifractal analysis. In this study, we have carried out fractal and multifractal studies using detrended fluctuation analysis (DFA) and multifractal DFA (MFDFA) respectively. While the DFA primarily facili...

The extra-terrestrial physical processes and morphological features of different phases of geomagnetic storms are well known. The degree of stochasticity in the physical processes associated with the main phase and recovery phase of geomagnetic storms can be effectively studied with multifractal analysis. In this work, we have applied multifractal...

Multi-electrode resistivity imaging survey with 48 electrodes was carried out to assess the extent of salinity inland, in the shallow subsurface in Nellore district, Andhra Pradesh, in the Eastern Ghats Mobile Belt (EGMB) region. Resistivity data were recorded using Wenner–Schlumberger configuration at nine sites along a profile of about 55 km in l...

Complete and anticipation synchronization of nonlinear oscillators from different origins is attempted experimentally. This involves coupling these heterogeneous oscillators to a common dynamical environment. Initially, this phenomenon was studied using two parameter mismatched Chua circuits. Subsequently, three different timeseries: a) x variable...

The Malwa Plateau in Shajapur district in Madhya Pradesh faces drought-like situation annually due to high surface runoff, evapo-transpiration and poor land use practices. The Salari watershed is one of the severely affected catchments within the Malwa Plateau that needs an urgent water resource development plan to support human life and restore ec...

The subject of wavelet analysis and fractal analysis is fast developing and has drawn a great deal of attention in varied disciplines of science and engineering. Over the past couple of decades, wavelets, multiresolution, and multifractal analyses have been formalized into a thorough mathematical framework and have found a variety of applications w...

In this chapter we introduce complex wavelets and their application to study the phase characteristics of decadal variations of geomagnetic data. We apply real and complex wavelets to the geomagnetic east-west component data of about 75 years, recorded at 74 global magnetic observatories to study the occurrence or non-occurrence of well reported gl...

In this chapter, we discuss the fundamental concepts of wavelets and fractals and their use in various branches of geosciences research, without much of the mathematical rigor. Wavelets and fractals, developed based on their simple characteristics and mathematical concepts, have revolutionized the understanding of chaotic and non-stationary geophys...

The physical and chemical phase transitions at upper mantle depths under high temperature and pressure conditions result in abrupt jumps in seismic wave velocity and electrical conductivity. Understanding these phenomena and the associated microstructural formation and evolution, which are responsible for such changes, are of utmost interest to the...

The naturally produced geomagnetic eld variations recorded at the earth’s surface or at satellite altitudes is of dual origin: external and internal. The external part originates from the current systems generated in the ionosphere and the distant magnetosphere by the interaction of the solar wind with them. As a result, different types of geomagne...

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 Mag...

We apply continuous wavelet transform technique to the full decade (2001–2010) of CHAMP vector magnetic data from 55417 tracks, to search for evidences of external source field signatures that are either misunderstood or ignored in modern magnetic field models.We show that satellite magnetic time-series, after subtracting the main and lithospheric...

Step-Frequency GPR (SFGPR) investigations were carried out at the location of a crude oil storage tank at a petroleum refinery. The storage tank was founded on an elevated platform (tank-pad). Subsidence of a portion of the tank-pad led to cracking of its bottom steel plates and subsequent leakage of crude oil. SFGPR imaging was done within and out...

Geophysical well-log (bore-hole) data facilitate understanding of the physical properties of the subsurface formations as a function of depth measured in a well. In the present study, the wavelet transformation technique was applied to the well-log data of three wells in the Bombay High oil field, India, in order to identify depths to the tops of o...

We provide a new hypothesis for the deep subsurface structures near the Bhuj 2001 earthquake region based on magnetotelluric (MT) investigations carried out close to the epicentre zone. 2-D inversion of broad-band MT data of two profiles of lengths 32 km (AA') and 52 km (BB') revealed a thick (˜3 km) highly conductive (1-4 Ω-m) surface layer of flu...

Electromagnetic (EM) induction in the Earth by time-varying geomagnetic field variations at different frequencies facilitates to look into different layers of the Earth from surface up to upper mantle depths and beyond using electrical conductivity as a diagnostic parameter. Because of their ability to penetrate to greater depths, long period geoma...

Electromagnetic induction (EM) studies are the only geophysical method available to investigate deep Earth electrical conductivity structure. Owing to their adequate spatial and temporal coverage, satellite magnetic data play a major role in such type of studies. In this regard, a good understanding and characterization of the large scale external...

The penetration of magnetospheric electric fields to the magnetic equator has been investigated for two intense magnetic storms that occurred on 31 March 2001 and 6 November 2001. The digital ground magnetic data from equatorial station Tirunelveli (TIR, 0.17°S geomagnetic latitude (GML)) and low-latitude station Alibag (ABG, 10.17°N GML) have been...

In an attempt to locate the presence of possible groundwater resource regions in the semi-arid North-East Brazil, an integrated survey including aeromagnetic and magnetotelluric (MT) studies have been undertaken in the Guaribas region and only MT survey in the Caracol region. In the Guaribas region the aeromagnetic data, its analytic signal and Eul...

Continuous wavelet transformation has been performed on resistivity, density, velocity, neutron-porosity and gamma-ray log data sets to determine the space-localization of oil and/or gas formation zones (pay zones) beneath the Bombay High oil field, India. We have used a variety of wavelets to determine the optimum wavelets that best characterize t...

In the East Gondwanaland reconstruction, India and Antarctica were considered to be juxtaposed since Mesoproterozoic; the Eastern Ghats Mobile Belt (EGMB) was forming a contiguous terrain with the Rayner Complex of the Enderby Land. However, recent studies indicate that the EGMB was never a part of the Indian Peninsula prior to the Neoproterozoic t...

Geophysical well-log (bore-hole) data represent the rock physical properties as a function of depth measured in a well. They aid in demarcating the subsurface horizons, identifying abrupt changes in physical properties of rocks and locating cyclicity (if any) in stratal succession. Rocks document their depositional history, which geoscientists unfo...

The quiet-day geomagnetic field variation data from the recently commissioned Nagpur geomagnetic observatory, which has augmented the currently active latitudinal chain of Indian magnetic observatories, are analysed for the year 1993- The variations for diurnal frequencies (Sq) recorded at Nagpur do not follow the expected trend with latitude. This...

We have utilized solar quiet daily variation (Sq) data recorded at a network of temporary and permanent magnetic observatories, operated along the western Pacific coast, in the 210° Magnetic Meridian (MM) region, spanning both hemispheres. The selected data sets correspond to solar-quiet year 1996. We have determined the ionospheric source current...

Estimates of the C-response function were determined by Z: H method to obtain conductivity and depth values for a substitute perfect conductor (conductosphere) beneath the Indian region, utilizing geomagnetic variations at periods of 27-day and its harmonics. Two and half years of continuous geomagnetic data were utilized. These data were recorded...

The effect of source field geometry on the response function (ΔZ/ΔH), used in geomagnetic depth sounding to decipher lateral conductivity distribution within the earth is highlighted with the help of contour plots of ΔZ/ΔH ratios for day and nighttime short-period fluctuations recorded through a large-scale magnetometer array operated in the equato...

The sensitivity of airborne and satellite borne electromagnetic surveys depends on the changes in the electrical properties of earth. These electrical properties vary significantly with various physical parameters in the extended frequency of electromagnetic signals. In the present paper, the effectiveness of electrical properties in the airborne a...