Contents
of January, 2000 - Vol. XXI No.1
CONCENTRIC AND RADIAL UPWARPS
AND DOWNWARPS: CRUSTAL ARCHITECHTURE OF THE INDIAN SHIELD FROM
GRAVITY MAPS
M. Kesavamani, C. Ramachandran and R.M.C. Prasad
IMAGE DISPLAY AND TONE AND TEXTURE
IN AEROMAGNETIC DATA
Duncan R. Cowan, Sam Bullock, Sheila Cowan, Linda A. Tompkins and Mike
Dentith
STATISTICAL ANALYSIS AND VISUALISATION
OF GOLD MINE DATA : A CASE STUDY OF KOLAR
GOLD MINE
N.K. Indira and K.S. Yajnik
AN INTERACTIVE COMPUTER PACKAGE
FOR MODELLING THE CRUSTAL STRUCTURE FROM BOUGUER ANOMALIES:METHODOLOGY AND APPLICATION
C. Visweswara Rao and E. Rajendra Prasad
S.K. Laskar
CRUSTAL STRUCTURE OF CHATTISGARH
REGION, MADHYA PRADESH, INDIA
EFFECT OF METEOROLOGICAL PARAMETERS ON RADON EMANATION AT
PALAMPUR (H.P.)
Anand K. Sharma, Vivek Walia and H.S. Virk
CONCENTRIC AND RADIAL UPWARPS AND DOWNWARPS: CRUSTAL ARCHITECHTURE
OF THE INDIAN SHIELD FROM GRAVITY MAPS
M. Kesavamani, C. Ramachandran and R.M.C. Prasad
Geophysics Division, Geological Survey of
India, Bandlaguda Complex, Hyderabad - 500 068, India.
Abstract
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IMAGE DISPLAY AND TONE
AND TEXTURE IN AEROMAGNETIC DATA
Duncan
R. Cowan, Sam Bullock*, Sheila Cowan, Linda A. Tompkins** and Mike Dentith***
Cowan Geodata Services, 12 Edna Road,
Dalkeith, W.A. 6009, Australia
*Kevron Pty Ltd, Hill Street, East Perth. W.A.,
**Terrasense
Pty Ltd., 25 Lochee Street, Mosman Park, W.A. 6012, Australia
***Dept
of Geology & Geophysics, University of Western Australia, Nedlands, W.A.
6907, Australia
Abstract
Qualitative aeromagnetic interpretation
using high-resolution filtered images is essentially a pattern recognition
technique involving identification of magnetic elements from changes in
magnetic relief and magnetic texture. Magnetic relief consists of anomaly
amplitude and shape and is relatively objective. Magnetic texture consists of
shape, size and continuity of adjacent anomalies and is more subjective.
Amplitude in image processing equates to tone, the relative brightness of
individual pixels. Texture refers to the spatial/statistical distribution of
the tones, so it is fundamentally different from tone, which is defined at one
location (pixel) while texture occurs over some finite area and hence requires
some finite number of pixels to represent it. Texture can occur at several
scales and larger scale aggregates are sometimes described as structure to
distinguish them from smaller scale texture variations. The spatial arrangement
of contrasting tones and textures within an image are referred to as patterns.
An experienced interpreter can recognise type patterns characteristic of the
magnetic expression of geological features.
Conventional filters such as vertical
derivatives respond primarily to the amplitude content of the data and have
problems with large dynamic range and have limited ability to enhance low
amplitude, subtle anomalies. AGC filters while reducing amplitude dependence
tend to amplify noise in the data, are relatively band limited and are mainly
dominated by texture. A range of filters have been developed to try to overcome
the limitations of conventional filtering and enhance tonal and textural
attributes simultaneously. Separation (layer) filters, grey-level co-occurrence
texture filters and the gradient tilt angle all perform better than
conventional filters but have very different enhancement characteristics with
varying degrees of tonal/textural information content amplification.
The various filters were tested on
aeromagnetic data covering the Lake Mackay, Northern Territory, Australia
1:250,000 map sheet. It was concluded that the different filters have different
amplitude and wavelength responses and the results are complementary. The GLCM
texture filter probably provided the best enhancement of subtle low amplitude
anomalies but had little tonal information content limiting the effectiveness
of the filter in the magnetically active areas. The gradient tilt angle
provides good textural content with more tonal content than the GLCM filters.
Combining two filters with different bandwidths and amplification factors such
as the separation filter and gradient tilt angle filter is a good compromise,
providing good enhancement of textural information while preserving enough
tonal or amplitude information to discriminate major magneto-tectonic units.
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STATISTICAL ANALYSIS AND VISUALISATION OF GOLD MINE DATA : A CASE
STUDY OF KOLAR GOLD MINE
N.K.
Indira and K.S. Yajnik*
C-MMACS, NAL Belur Campus, Bangalore – 560
037, India.
*Former
Head, C-MMACS, Apt F2, Regal Manor, 2/1 Bride St., Langford town,
Bangalore
– 560 025, India.
Abstract
A case study based on the statistical
analysis of the Footwall Lode of the Champion Reef Mine of the Kolar Gold Mines
has been made. It has been found that the gold deposition in terms of the grade
values follows a univariate lognormal distribution as does the accumulation. On
the basis of the distribution of the width of the lode, the analysis is
extended further to support the possible existence of two different lodes using
the F-test, two sample t-test and Kolmogorov- Smirnov two sample test. The data
is geometrically modelled on a graphic workstation.
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AN INTERACTIVE COMPUTER
PACKAGE FOR MODELLING THE CRUSTAL STRUCTURE FROM BOUGUER ANOMALIES:METHODOLOGY
AND APPLICATION
C.
Visweswara Rao and E. Rajendra Prasad
Department of Geophysics, Andhra University,
Visakhapatnam- 530003
Abstract
---An interactive computer package for
interpreting Bouguer gravity anomaly in terms of crustal structure has been
developed. Power spectral analysis, regression analysis, the digital filter for
separating lower and higher wavelength components and the properties of sin x/x
function are used to formulate the methodology for crustal modelling. Two
Bouguer anomaly profiles, viz., Koyna I (Guhagar – Chorochi) and Koyna II
(Kelsi – Loni) are re-interpreted using the developed package and the results
are in general agreement with those of the earlier analyses of these profiles
establishing the utility of the package.
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A NOTE ON UNIQUENESS
OF DEPTH DETERMINATION FROM OBSERVED POTENTIAL FIELD DATA
S.K.
Laskar
Department of Mathematical Sciences, Tezpur
University, Tezpur – 784001, Assam
Abstract
An attempt is made to discuss uniqueness
of depth determination from observed potential field data on reproducing the
field by simple layer density s belonging to a horizontal half-space boundary
S that lies below the datum level 
. Assuming
that the s belonging to S reproduces
the field over as S gradually moves
downward and crosses the causative mass m, it is theoretically shown that
the s exhibits a smooth continuous behavior when S
is shallower than m and an erratic behavior when S is partially or wholly
below it. The depth to the shallowest S with an erratic s defines the depth to the top of the causative mass and this depth
is unique.
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CRUSTAL STRUCTURE OF CHATTISGARH REGION, MADHYA PRADESH, INDIA
S.Srinivas*,
A.S.K.Murthy**, G.S.Yadav** and K.M.Srivastava**
* Presently with National Geophysical Research
Institute, Uppal Road, Hyderabad-500007.
** Department of Geophysics, Banaras Hindu University, Varanasi - 221 005.
Abstract
A regional gravity anomaly profile
across the Chattisgarh region is studied in terms of basin configuration and
crustal structure. Two gravity models are inferred viz., a two layered crustal
model and a differentiated crustal model, out of which the differential crustal
model appears to be realistic. Both the models indicate a maximum thickness of
3.5 km for the sediments and an up-warp of 2 km in the moho under the
Chattisgarh basin.
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EFFECT OF METEOROLOGICAL PARAMETERS ON RADON EMANATION AT PALAMPUR
(H.P.)
Anand K. Sharma, Vivek Walia and H.S. Virk
Department of Physics, Guru Nanak Dev
University, Amritsar-143005, India
Abstract
Effect of meteorological parameters on
radon emanation in the soil-gas at Palampur station has been studied for time
window March 1993 to March 1995 and the results obtained are correlated in
terms of radon fluctuations. The radon value is found to be positively
correlated with temperature, relative humidity and mild rainfall whereas it
shows inverse relationship with evaporation, wind velocity and heavy rainfall.
The overall correlation is found to be week resulting in a cumulative effect of
10-20% on radon emanation at the most. Other parameters, e.g., sunshine hours
and vapour pressure cause negligible effect on radon emanation rate.