Indrajit G. Roy

Spaceage Geoconsulting · Research

Episodes of tectonic activities since Archaean time in one of the oldest craton, the eastern Yilgarn Craton of Western Australia, have left a complex pattern in the architectural settings. Insights of the crustal scale archi�tectural settings of the Craton have been made through geophysical data modelling and imaging using high res�olution aeromagn...

The aspects of gravity modelling with a semi-infinite vertical line of mass as an approximation to the model of semi-infinite vertical cylinder is critically reviewed. The brief outline of the derivations of gravity response due to both type of models, such as the semi-infinite vertical line of mass and vertical right circular cylinder, is given. T...

Geophysics is relatively a new discipline in comparison to physics or geology. Contrary to general perception as an ancillary to geology, the discipline has been developed with a distinct focus of using the principles and methods of physics for the earth processes. Geophysics was born in the nineteenth century as a necessary element of theoretical...

A standard experimental setup for Inelastic Electron Tunneling Spectroscopy (IETS) performs the measurement of the second derivative of the current with respect to the voltage (d2I/dV2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepacka...

A robust method of estimating second vertical derivative of 2D potential field data is proposed. The proposed method uses a 2D variant of Savitzky‐Golay derivative filtering. The design of 2D Savitzky‐Golay derivative filter, unlike its 1D counterpart, is a non trivial exercise. This is due to inherent complexity associated with 2D polynomial regre...

The potable groundwater, sans any contaminant, is a valuable resource. An attempt of investigating groundwater resources and delineating contaminant plume, if there is any, within subsurface plays significant role in the human society in improving general economy, human development index and public health. Sometimes severe economic constraints dete...

I propose a simple and sufficiently robust data based semi-automated interpretation of total magnetic intensity (TMI) profile to delineate an isolated fracture or a fractured zone embedded within a homogeneous host medium. The interpretation technique which is based on the premise of induced magnetisation uses a model of thin two dimensional dippin...

We interpret the legacy ship-track magnetic and bathymetric profile data to investigate the role of the lithospheric scale West Andaman Fault (WAF) in the dormant Narcondam and active Barren Island volcanoes. We use data-based automated interpretation of total magnetic intensity (TMI) profiles using a contact model in order to delineate geometrical...

We propose a strategy in designing an optimal set of filter parameters, such as the order of interpolating polynomial and the filter length for Savitzky-Golay derivative filter. The proposed strategy is based on the principle of parsimony while satisfying the optimality conditions. The optimality conditions are based on Durbin-Watson lag-1 test sta...

We demonstrate a strategy of investigating recharge potential of a shallow aquifer in a hard rock terrain through flow in a fractured zone using self-potential (SP) anomaly and other ancillary (published) data related to the area of investigation. Our study area is Vilarelho da Raia, northern Portugal which possesses a shallow aquifer within a gran...

The paper proposes estimating Hilbert transform of geophysical time series via Hilbert-Noda transform. The Hilbert-Noda transformation matrix which is a skew symmetric matrix having zero values on the diagonal elements has a Toeplitz structure. The proposed paper enumerates some of the properties of the Hilbert-Noda transformation matrix. A numeric...

We propose a simple technique of robust estimation of first order derivative of a discrete set of noisy measurements. The proposed technique uses conventional numerical tools, such as the first order finite difference and the natural cubic spline on evenly spaced noisy dataset and provides robust estimation of the first order derivative. We also pr...

The dawn of computational geophysics struck almost immediately with the birth of ENIAC, a first electronic computer being used for scientific purposes. The first weather prediction model was developed on ENIAC by the researchers from the Institute of Advanced Studies (IAS), Princeton University. Since then computational methods in geophysics had a...

Groundwater has a significant impact especially in improving the rural economy and the rural health. In the recent years, many South Asian countries including India are experiencing tremendous water crunch due to variability in the climatic pattern. In many situations, small water bodies on the surface are completely dried up and the groundwater le...

Differential conductance is a key to characterizing solid-state device. Estimation of differential conductance from current-voltage characteristic curve amounts to estimate the first order derivative from a discrete set of current voltage measurements of the device under test. Conventional difference method in estimating derivative is inadequate wh...

I have developed an improved practical method for interpreting a symmetrical-shaped potential field anomaly due to an isolated source body of regular geometric configuration. The method uses the first-order horizontal derivative of the logarithmically transformed absolute value of the anomaly in estimating the source-body parameters, such as the lo...

An automated method interpreting buried dipping contact model using total gradient and tilt angle transformation of the total magnetic intensity profile data. The workflow of processing total magnetic intensity data and the design detail of the algorithm for robust estimation of total gradient and tilt-angle of noise-contaminated total magnetic int...

The relation in which the vertical and horizontal gradients of potential field data measured along a profile across a two-dimensional source are a Hilbert transform pair is re-established using complex domain mathematics. In addition, a relation between the measured field and its vertical gradient in terms of a closed-form formula is also establish...

Enhancing resolution in spectral response and an ability to differentiate spectral mixing in delineating the endmembers from the spectral response are central to the spectral data analysis. First and higher order derivatives analysis of absorbance and reflectance spectral data is commonly used techniques in differentiating the spectral mixing. But...

Seismic source characteristics in the Kachchh rift basin and Saurashtra horst tectonic blocks in the stable continental region (SCR) of western peninsular India are studied using the earthquake catalog data for the period 2006–2011 recorded by a 52-station broadband seismic network known as Gujarat State Network (GSNet) running by Institute of Seis...

The interpretation of tilt angle transformed total magnetic intensity data for a dipping contact model is studied, where it is shown that if the trace of a dipping contact on a horizontal surface is determined then other source parameters, such as the dip and the depth of burial of the contact can be estimated using simple formulas. The trace of th...

We developed a novel technique of robust estimation of the discrete Hilbert transform (DHT) of noisy geophysical data. The technique used the sinc method, in which the data were transformed via conformal mapping and the sinc bases were determined by solving a linear matrix equation. A transformation rule was presented for selecting a suitable confo...

Accurate and robust computation of gradients of potential field data are crucial in potential field-data processing and also in data-based interpretation. The standard Fourier domain approach in gradient computation, although computationally efficient, is flawed due to its sensitivity to noise in the data. A robust space domain technique in computi...

The Mt Isa–McArthur region is renowned for a range of commodities and deposit types of world-class proportions. The region is described here in the context of a ‘mineral system,’ through consideration of processes that operate across a range of scales, from geodynamics and crustal architecture, to fluid sources, pathways, drivers and depositional p...

Deep seismic reflection surveys in north Queensland that were collected in 2006 and 2007 discovered a previously unknown sedimentary basin, now named the Millungera Basin, which is completely covered by a thin succession of sediments of the Jurassic–Cretaceous, Eromanga-Carpentaria Basin. Interpretation of regional aeromagnetic data suggests that t...

Integrated interpretation using potential field and reflection seismic data of Georgina Basin of Northern territory, Australia

World-class mineral systems, such as those found in the Archaean eastern Yilgarn Craton, are the product of enormous energy and mass-flux systems driven by lithospheric-scale processes. These processes can create big footprints or signatures in the lithosphere, which can be observed at a range of scales and via a variety of methods: including geoph...

The Laverton region, located in the eastern Yilgarn Craton (EYC) Western Australia, is second only to the Kalgoorlie region for gold endowment. The integration of high-density, potential-field data, regional- and camp-scale seismic reflection data, regional- and mine-scale structural analysis, and geochronologically-constrained stratigraphy, provid...

In 2008, as part of its Onshore Energy Security Program, Geoscience Australia, in conjunction with AuScope, Primary Industries and Resources South Australia (PIRSA) and the Northern Territory Geological Survey, acquired 634 km of vibroseis-source, deep seismic reflection data and gravity data along a single traverse from about 25 km southeast of Er...

We describe a numerical study performed to appraise the ability of seismic amplitude data to infer the time evolution of pore pressure and fluid saturation due to hydrocarbon production. To this end, we construct a synthetic, spatially heterogeneous hydrocarbon reservoir model that is subject to numerical simulation of multiphase fluid flow. Hydroc...

An algorithm of model-based nonlinear inversion scheme with applications on geophysical examples is proposed. In the framework of classical least squares optimization, the algorithm uses adaptively controlled smoothness constraint in an iterative minimization scheme through an appropriate selection of regularization parameter. A new formula in comp...

The aim of seismic waveform inversion is to estimate the elastic properties of the Earth's subsurface layers from recordings of seismic waveform data. This is usually accomplished by using constrained optimization often based on very simplistic assumptions. Full waveform inversion uses a more accurate wave propagation model but is extremely difficu...

Seismic waveform inversion can be an important tool for reservoir characterization because high-resolution (within the seismic-frequency band) images of elastic parameters are obtainable from good quality seismic data. A detailed description of the velocity field with both high- and low-frequency variations is essential for delineating elastic prop...

Seismic waveform inversion is a highly challenging task. Nonlinearity, nonuniqueness, and robustness issues tend to make the problem computationally intractable. We have developed a simple regularized Gauss-Newton-type algorithm for the inversion of seismic data that addresses several of these issues. The salient features of our algorithm include a...

Summary Pre-stack seismic waveform inversion is a highly challenging task. Non-linearity and non-uniqueness together with compute intensive forward modeling make the problem close to intractable. We report on the results obtained with a new approach to pre-stack inversion based on a gradient descent scheme that makes use of innovative gradient calc...

Summary Like many other inverse problems, pre-stack waveform inversion algorithms need to address the issues of stability, non-uniqueness, and robustness. Regularization is crucial to obtaining stable solutions. In addition, while using a gradient descent approach to a non-linear problem, efficient gradient calculation algorithms need to be develop...

A robust descent type algorithm through adaptive regularization is designed to solve a geophysical inverse problem. The scheme uses a regularized descent direction which is obtained through minimization of smoothed functional in every iterative step. The step length factor is chosen using Armijo's rule. Numerical experiment conducted to invert synt...