Coal reserve in India approximates around 211 billons tones of which more than
99.5% are estimated from Gondwana Coalfields. Jharia Coalfields (JCF) is one
of the most important coalfields in India, located in Dhanbad district, between
latitude 23° 39' to 23° 48' N and longitude 86° 11' to 86° 27'
E. This is the most exploited coalfield because of available metallurgical grade
coal reserves. Mining in this coalfield was initially in the hands of private
entrepreneurs, who had limited resources and lack of desire for scientific mining.
The mining method comprised of both opencast as well as underground. There are
23 large underground and nine large open cast mines. The mining activities in
these coalfields started in 1894 and had really intensified in 1925 (Saxena,
Open-pit mining, also known as open-cast mining, open-cut mining and strip
mining, refers to a method of extracting rock or minerals from the earth by
their removal from an open pit or borrow. Often the mineral deposit is covered
by soil, which must first be stripped off, usually by large machines such as
walking draglines and bucket-wheel excavators. The ore deposit is then broken
up by explosives. The practice of open cast mining in the coal seams of the
Jharia coalfields has left a legacy of pits and overburden dumps. The opencast
mining areas were not backfilled, so large void is present in the form of abandoned
mining. It is also projected that if proper reclamation measure is not followed,
a total of 200 sq. km will be converted to badland topography:100 km2
as quarried land and another 100 km2 as overburden dump area (Ghosh
et al., 1998).
Monitoring of changes in topography is one of the main requirements of planners
and managers (Saxena, 1994). The topographical changes
due to open cast mining should be mapped properly in order to facilitate the
reclamation process. Thus the need for deriving present date elevation models
of better accuracy arises. There are various approaches of deriving updated
elevation models, namely direct survey, Aerial photogrammetry, Satellite photogrammetry,
Radargrammetry, Interferrometry and Laser Altimetry (Edward
et al., 2001).
With high resolution satellites with stereo images, satellite photogrammetric
techniques emerge as a good solution for getting cost effective and high accuracy
elevation models (Lutes, 2006).
Cartosat-1, launched in May 2005, has two cameras to collect stereo data at
better than 2.5 m resolution: one near-nadir-looking and the other forward-looking
(Nandakumar et al., 2005; Raghava
Murthy, 2005). A single stereo pair covers a ground area of about 800 sq.
km The two stereo components, labeled AFT and FORE images to indicate the look
direction, are designed to produce Digital Elevation Models (Krishnaswamy
and Kalyanaraman, 2002; Kumar, 2006).
The basic aim of the research is to map topographical changes induced due to open cast mining activity in Jharia Coal field area. To fulfill this broad objective, following sub-objectives needs to be carried out:
To generate DEM from SOI 1:50,000 toposheet surveyed in 1973-1974
process high resolution satellite stereo dataset for DEM generation
detect topographical change in the area
MATERIALS AND METHODS
Study area: Jharia coalfield is located in the eastern part of India, about 250 km NW of Kolkata. The Coalfield is lying North of the Damodar river, covers an area of about 450 km2 and stretches between latitudes 23°38' N and 23°50'N and longitudes 86°07'E to 86°30'E. Figure 1 shows the Jharia coal fields which was investigated for the topographical change analysis. The study was conducted in 2008.
high resolution panchromatic stereo pair from the CARTOSAT I satellite
with a spatial resolution of 2.5 m acquired on April 04th, 2006 Path:
578, Row: 287 (Fig. 2a)
Toposheet 73 I/1, 2, 5 and 6 (Fig. 2b)
points, spot heights
Methodology: The elevation models used for final analysis were generated using two data sources- contour information and spot heights from SOI topo maps and stereo images procured from space based sensor. The capabilities of ERDAS IMAGINE v 9.1 were utilized for processing and final analysis of the data. Photogrammetric module (Leica Photogrammetric Suite) was exploited to automatically extract elevation information from CARTOSAT I stereo data product. The overall methodology adopted in the study is presented Fig. 3. The Cartosat-stereo dataset was processed and DEM was generated. The DEM was also generated using SOI toposheets and the change was analysed. Elevation Model for the study area was generated by digitizing the contours of SOI toposheet as well as from Stereo restitution of the stereo dataset:
and Aft looking image data can be obtained associated with metadata, which
can be interpreted to obtain interior orientation parameters
data collected from topomap, GPS measured control points for exterior
orientation of image pair
extraction of DEM after 3-D modeling process, interpolation, proper modification
and accuracy assessment
information was extracted from SOI toposheets at 1:50,000 scale and used
to create raster elevation model. Related processing and accuracy assessment
The stereo pair was oriented using Rational Polynomials supplied. The orbital parameters were calculated and DSM was extracted. Orbital parameters were refined using few Ground Control Points (10 in number). Ground Control information for this area was collected from the topomaps Surveyed by the SOI. The exterior orientation parameters were refined using GCPs and automatically generated tie points through triangulation. Figure 4 shows the distribution of control points within the study area. The GCPs were choosen in such a maneer so as to provide control in all parts of the image.
The uncontrolled block exhibited significant Y parallax of up to 50 pixels. Figure 5 shows elevation model generated with uncontrolled block, which exhibits major errors. The heights in this elevation model are erroneous and misleading. The E.O. parameters were refined using automatically generated tie points. The triangulation error thus obtained was 1.7 pixels. The error in X, Y and Z were in the range of 10-100 m. The controlled block (GCPs +tie points) exhibited a triangulation error of 0.2 pixels. The error in X and Y ranged from 0.3 to 15 m whereas in Z it was 0.1 to 6 m. The point exhibiting maximum error may be due to placement uncertainty in fore image as the image was radiometrically smoother and geometrically distorted.
The elevation information extracted using the uncontrolled block resulted in
prominent errors in many areas. The uncontrolled elevation model (Fig.
5) shows problems in the depiction of minor topographic features. The matching
process is more robust when Ground Control information was incorporated. The
topography of the area, even small residual hills and minor streams are clearly
seen in the refined elevation model (Fig. 5). In addition
to the elevation model generated using high resolution image pair SOI topomaps(1;
50000 scale) were scanned, merged and digitized to create surface map to be
used for estimating topographical change areas (Fig. 6).
||(a) CARTOSAT 1 Stereo data of Jharia and (b) SOI Toposheet
73 I/1,2,5 and 6
||GCP distributions in area
elevation model, Controlled elevation model
Elevation Model using SOI toposheet
The reference and current digital elevation models were compared to find out topographic
change areas in the study areas.
ANALYSIS AND RESULTS
In the virtual GIS module of ERDAS IMAGINE 9.1 a virtual 3-D view was created
to highlight the subsidence areas (Fig. 7). Figure
7 clearly shows large voids in the topography in and around the area. The
reference DEM (DEM from SOI toposheet surveyed in 1973-74) was compared with
satellite image derived DEM (Acquired on April 4th 2006). The difference map
was generated which highlighted the open cast mining areas as compared to 1973-74
topography (Fig. 8). The results of the study were compared
with published data about open cast mine areas.
3D model of the area showing subsidence
change area in Jharia Coal Fields
Cast mining areas in Jharia Coal Mines
Figure 9 shows published data about open cast mining areas
within Jharia Coal Field. When compared with the topographical change areas,
it is exhibited that the areas taken out by this technique are matching the
areas of open cast mines with 89% confidence level. Thus the results obtained
were in concurrence with the existing map.
The study highlights usefulness of high resolution satellite derived DEM for topographical change analysis. The resolution of reference DEM is not comparable to that of satellite derived DEM. It is recommended to use better resolution DEM as reference if possible. Further analysis using image data varying spatially and temporally can be used for better understanding of the pattern of overburden dump areas and pits.