January, 2007

January, 2007   ||  Volume 11 No.1

Airborne Geophysics and the Indian Scenario


Deputy Director General (Geophysics)-Retd., GSI, 273 Indraprastha Colony, Baghamberpet, Hyderabad – 500 013

Airborne Geophysics is a powerful means available to the earth scientist for investigating very large areas rapidly. The broad view of the earth that the airborne perspective provides has been well recognised since the early days of balloon photography and military reconnaissance. Compared with ground-based methods, airborne techniques offer the advantages of rapid acquisition of data at scales that are suitable for many geophysical problems. Further, airborne surveys provide the capability of traversing regions that are otherwise difficult or impossible to cover. Airborne methods are advantageous for surveys over areas that are physically accessible but that have social, economic, or political barriers or environmentally hazardous.
Systematic and precise airborne geophysical surveys may be said to have started immediately after the Second World War with the development of an airborne fluxegate magnetometer by Vacquir (Dobrin 1952). By about 1955 countries such as the USA, Canada, Austarlia etc began using the airborne magnetometer systematically. In the following years several contracting companies made considerable R & D effort to develop capabilities for meeting the precise requirements for airborne surveys. The 1960s saw the deployment of proton precession magnetometer for aeromagnetic surveys and utilization of Doppler navigational aids for more accurate position fixing. There has also been considerable growth with regard to radiometric surveys by deploying multi-channel instruments for obtaining data on ground concentrations of potassium, thorium and uranium. The air borne geophysical techniques have undergone continuous development including transition to digital technology and refinement of the surveying methods in the 1980s and 1990s. In the case of airborne electromagnetic method (AEM) the numerous configurations that existed in the initial stages were considerably reduced and only two types of systems are mainly in vogue now. Major applications of airborne geophysics in the past decade have seen an increase in emphasis for environmental, and engineering applications, including hazard mapping.


Diagnostic study of monsoon depression and examination of energetics produced by two schemes (2-D NVA and 3-D NVA) over Indian Region
S.G.Narkhedkar, S.K.Sinha, P.L.Kulkarni, J.R.Kulkarni and P.N.Mahajan
Indian Institute of Tropical Meteorology, Dr. Homi Bhabha Road, Pashan, Pune – 411 008
E-mail : narkhed@tropmet.res.in

Following Sasaki (1958) two objective analysis schemes viz. two dimensional Numerical Variational Analysis (2-D NVA) and three dimensional Numerical Variational Analysis (3-D NVA) have been developed by Sinha, Narkhedkar & Rajamani (1998); Sinha et al., (2003) and Narkhedkar & Sinha (2000) over India and adjoining region. NVA is the scheme that produces the analysed data in balance. The 2-D NVA uses geopotential height and wind data simultaneously to produce analysed height and wind field at grid points whereas 3-D NVA allows temperature data to influence the analysis of height and wind fields. Both the schemes have been tested for two to three synoptic situations and have performed well in depicting the systems. In this study the performances of these two analysis schemes in context with energetics have been assessed in depicting the features of the synoptic scale systems viz. Tropical Easterly Jet, Sub Tropical Westerly Jet etc. prevailing over Indian and adjoining region in the monsoon season. The analyses produced by these two schemes have been examined to study the energetics of a monsoon depression which formed over head Bay of Bengal. The energy terms viz. available potential and kinetic energy (both zonal and eddy part) and their conversion terms have been computed. The analyses of these terms for both schemes showed that they are in well accordance with the earlier studies made by other researchers over Indian region. The analyses produced by both the schemes were able to depict the system very well in context with the energy terms that have been computed from the analysed field produced by them. However, due to the inclusion of temperature field 3-D NVA scheme has produced higher values of energy terms compared to 2-D NVA scheme. The influence of analysed upper and lower tropospheric temperature fields on the energy terms in generation of the energy and maintaining the circulation patterns have been studied critically. It has been observed that during the period of depression the north-south temperature gradient was prominent at upper levels.

Analytical computation of Hydraulic Potentials due to Point, Line and Areal Sources over three - Layered Aquifer System

Rambhatla G.Sastry1 and Mathew K.Jose2
1Department of Earth Sciences, I.I.T, Roorkee-247667, India
E-mail: rgss1fes@iitr.ernet.in / rgssastry@yahoo.com; Fax: 91-1332-273560
2 National Institute of Hydrology, Jalvigyan Bhawan, Roorkee-247667, India
E-mail: mjose@nih.ernet.in; Fax: 91-1332-272123
1Corresponding author

Steady state analytical expressions for hydraulic potentials and streamlines of a three-layered aquifer system due to a point source recharging have been derived. By applying appropriate convolution techniques, respective expressions for a finite-length line and areal sources are arrived at. Then, the computational algorithms (i) 3LPNT- for a point source, (ii) 3LLIN- for a finite length line source and (iii) 3LARL- for an areal sourc have been designed.
Our simulation results for these three different sources, when compared with those by standard numerical groundwater flow model, MODFLOW indicate the cost-effectiveness of our approach both in terms of accuracy and computational speed.

A user friendly environment for the Spectral Analysis of Geomagnetic Data
Y.N.T.Seshagiri Rao
National Geophysical Research Institute, Hyderabad - 500 007

This paper describes a user-friendly Graphical User Interface also called Windows (You click and get something) environment or platform and computational paradigms developed using Java programming language for the spectral analysis of Geomagnetic Data. For the spectral analysis Digital Signal Processing methods such as Fast Fourier Transform (FFT), Cosine and Sine Transforms are used. The FFT transforms a function from the time domain to the frequency domain and is an extremely important and widely used method of extracting useful information from sampled signals. In the design of the system, the methodology used is Unified Modeling Language (UML), an advanced flowchart that uses Use Case Diagrams (UCD). The background and motivation is the automation of the entire process of obtaining spectra analysis.