An experience with ILWIS in connection with National Geochemical Mapping by Geological Survey of India 1 S. Ramamurthy Geodata Division, Eastern Region, Geological Survey of India, Dk-6, Sector-2, Kolkata-91(ramasoma@yahoo.com) 2 Drishya Opn: WB&AN, Eastern Region, Geological Survey of India, Dk-6, Sector-2, Kolkata-91(geodrish@gmail.com) Abstract The paper presents the initiative taken by the Geological Survey of India, Eastern Region, Kolkata to promote the usage of ILWIS, a Free and Open Source Software, in the National Geochemical Mapping Project. Some of the constraints at various stages of the project and some possible solutions from the use of ILWIS software and also the freely available spatial data in public domain like SRTM DEM and Remote Sensing data products (IRS 1D, Landsat etc.) and their relevance to the project are discussed. Collection of stream sediment samples in relatively flat terrain poses a major problem, as the topographic features including streams shown in the Survey of India toposheets are often obliterated/modified due to extensive anthropogenic activities. Dem Hydro processing tools have been of immense help in drainage extraction and ordering from the DEM. Merging of hillshade map generated from SRTM DEM and imagery also helped in choosing the sample locations. With the constraint of non availability of expensive software at every desktop for image processing and GIS, ILWIS is an excellent alternative. It has been used in a number of ways for the present study which include Georeferncing of thematic layers and bringing them to a common coordinate syste; plotting of the point data; generation of attribute maps, surfaces using various interpolation techniques, contour maps and classified rasters; study of dispersion patterns of elements and their spatial correlation; integration of various thematic layers and Map making. Various statistical analyses were also attempted using Statistics tools in ILWIS. The study area chosen for the above work falls in Degree sheet 73 I, in parts of West Bengal, India. As part the mission, around 30 officers of GSI have been trained in the use of ILWIS. Keywords- ngcm, gis, ilwis, srtm dem, irs-1d imagery, foss, dem hydroprocessing, raster and vector processing, map making. I. INTRODUCTION: In India geochemical mapping (National Geochemical Mapping-NGCM) was initiated by the Geological Survey of India (GSI) during 2001-2002 from the concept of creating a global geochemical database as per the guidelines of the International Geological Correlative programme (IGCP). The main objective of geochemical mapping project is to generate baseline geochemical data for the entire country for the use in various fields like managing and developing natural resources; addressing environmental issues, agricultural and human health NGCM Project and Constraints: Three main stages and the constraints being faced in executing the NGCM project are: Prefield : This stage includes collection of required information regarding the particular area (Topography, Geomorphology, Landuse &Landcover, Drainage, satellite image etc). During this stage major constraints encountered while dealing with digitl data (SRTM DEM, LU/LC etc.) Due to non-avalability of GIS and remote sensing software. During fieldwork: The main aim in this stage is to collect various geochemical samples like stream sediments (1Km 1Km grid), soil (C&R horizon in 5Km 5Km grid), water (5Km 5Km grid) and flood plane samples(if any). Main difficulties facing in this stage is identification of proper sample points due to change in topography by excessive anthropogenic activity. Many a times, the topographic features including streams shown on toposheets are either obliterated or modified. 1 P a g e
Post field: Post field activity considered as the backbone of the NGCM project, includes geochemical data interpretation and generation of various thematic maps like distribution map of elements and their spatial correlation, integration of various thematic layers, creation of surfaces/continous rasters using various interpolation techniques by means of that anomalous pattern of various elements. More than that systematical statistical analysis like descriptive statistics -median, mean, mode, standard Deviation, Kurtosis, Skewness etc and histogram, which depicts the type of distribution and data homogeneity. In addition, multivariate analysis of data depicts correlation among various elements/oxides. The constraint at this stage again is the non-availability of expensive proprietary GIS software for data processing and analysis. The paper presents the efforts being initiated by the Geological Survey of India in using Free and Open Source Software and the Public Domain spatial data for its National Geochemical Mapping Project. The paper presents the efforts being initiated by the Geological Survey of India in using Free and Open Source Software and the Public Domain spatial data for its National GeoChemical Mapping project. II. A. DATA FREE AND OPEN SOURCE DATA AND SOFTWARE Digital Elevation Model (DEM) of 90m resolution obtained from Shuttle Radar Terrain Mission (SRTM) is downloaded from the Global Land Cover Facility (GLCF) website glcf.umiacs.umd.edu which provides earth science data and products to help everyone to better understand the global environmental systems. In particular, the GLCF develops and distributes remotely sensed satellite data and products that explain land cover from the local to global scales. Primary data and products available at the GLCF are free to anyone. Online datasets can be accessed electronically through the Earth Science Data Interface (ESDI). The Shuttle Radar Topography Mission (SRTM) obtained elevation data on a near-global scale to generate the most complete high-resolution digital topographic database of Earth. SRTM consisted of a specially modified radar system that flew onboard the Space Shuttle Endeavour during an 11-day mission in February of 2000. SRTM is an international project spearheaded by the National Geospatial-Intelligence Agency (NGA), NASA, the Italian Space Agency (ASI) and the German Aerospace Center (DLR). There are three resolution outputs available, including 1 kilometer and 90 meter resolutions for the world and a 30 meter resolution for the US. GLCF serves the main USGS editions, plus has 'enhanced' editions as well as provides editions in WRS-2 tiles to approximate Landsat scenes. The IRS-1D multispectral data for the study area was downloaded from the Bhuvan website (http://bhuvan.nrsc.gov.in/bhuvan) Bhuvan, a Geoportal of Indian Space Research Organisation showcasing Indian imaging capabilities in multi-sensor, multi-platform and multitemporal domain. This Earth browser gives a gateway to explore and discover virtual earth in 3D space with specific emphasis on Indian Region. Bhuvan on its portal provides a range of services enabling visualization of various thematic data generated from myriad national missions and projects carried out by NRSC.. B. SOFTWARE We employed ILWIS for processing and analysis of data at various stages of the project implementation. ILWIS (Integrated Land and Water Information System) is a GIS / Remote sensing software for both vector and raster processing. ILWIS features include digitizing, editing, analysis and display of data as well as production of quality maps. ILWIS was initially developed and distributed by ITC Enschede (International Institute for Geo-Information Science and Earth Observation) in the Netherlands for use by its researchers and students, but since 1 July 2007 it has been distributed under the terms of the GNU General Public License and is thus free software. ILWIS is one of the most user-friendly integrated vector and raster software programmes currently available. ILWIS has some very powerful raster analysis modules, a high-precision and flexible vector and point digitizing module, a variety of very practical tools, as well as a great variety of user guides and training modules all available for downloading. The current version is ILWIS 3.8 Open. III. VARIOUS OPERATIONS EXECUTED USING ILWIS SOFTWARE DURING THE PROJECT: Georeferencing the toposheet and generation of 1km x 1km grid over the toposheet for the purpose of sample collection from each grid (Fig. 1 ) Defining projections and transformations as and when required Refining of the SRTM DEM by filling the sinks etc (Fig. 4) Generation of hillshade maps for better visualization of the terrain (Fig. 5 ) Extraction of drainage from the SRTM DEM using DEM Hydroprocessing tools (Fig. 6 & 7) and superimposing over the gridded toposheet for identification of sample locations. 2 P a g e
IRS-1D multiband imagery was imported to ILWIS and processed using image processing tools. False Color Composits (FCC) were generated (Fig. 3) for visualization and delineation of lithounits and lineaments. Merged with the DEM for better visualization of topography. The tentative locations identified for the sample collection were digitized and the co-ordinates were fed to the GPS. This would facilitate in directly accessing the sample point in the field. After receiving the analytical data in a spread sheet, the table was imported into ILWIS (Fig.8) Locational errors, if any, were identified and rectified by generating point map from the tabular data. Various statistical analysis (univariate and multivariate) was also attempted which include Descriptive statistical analysis (median, mean, mode, standard Deviation, Kurtosis, Skewness etc) and Histogram depicts the type of distribution and data homogeneity) Raster surfaces for each element were generated using various interpolation algorithms available in ILWIS software and the accuracy of the resulting rasters were validated by plotting the sample data over each rasters. (Fig.10 ) Based on the crustal abundance thresholds, the anomalies were demarcated for each element and classified (Discrete) Rasters were generated. (Fig. 11) Generation of contour (Isolines) maps for each element. Querying with conditional operator (iff: ) from multiple maps (Fig. 12 ) Raster to vector conversions Map making (Fig. 13) Fig 1 Georeferenced toposheet Fig.2 Georeferenced toposheet with overlay of 1km x 1km grid Fig.3. FCC of IRS -1D imagery (RGB: 5 4 3) 3 P a g e
IV. OUTPUTS Fig. 4. SRTM DEM (Sink filled) Fig.5. Hillshade map generated from SRTM DEM Fig. 6 Flow direction raster Fig. 7 Draingae network extracted from SRTM DEM Fig. 8 Table imported to ILWIS format Fig.9 Sample location map after rectifying the errors 4 P a g e
Fig.10 Copper distribution raster Fig.11 Classified Copper raster Fig. 12: Anomaly map of Cu AND Pb Fig. 13 Map composition with various map elements V. CONCLUSIONS ILWIS being a software which consists of Raster & Vector GIS and with robust image processing tools, the authors feel that this is one of the best alternate software for the National Geochemcial Mapping projects. Besides, there is plenty of very useful spatial data, both thematic and satellite imagery, in the public domain which can also be immensely useful in various earth science applications including Geochemical mapping. As part of this mission of propagation of use of ILWIS, around 30 officers of GSI State units based at Kolkata, Ranchi and Patna have been trained. VI. VII. ACKNOWLEDGEMENTS The authors wish to thank Dr Srinivas Madabhushi, Dy Director General, GSI ER, Kolkata for his constant encouragement in promoting the use of ILWIS and writing this paper. Thanks are also due to Dr Eswara Basappa, Director-In- Charge; Op: WB-An and other colleagues for the support extended in implementation ILWIS software for NGCM project. VIII. REFERENCES [1] http://glcf.umiacs.umd.edu/ [2] http://bhuvan.nrsc.gov.in/bhuvan/. [3] ILWIS Help documentation [4] Wikipedia, the free encyclopedia 5 P a g e
IX. AUTHORS PROFILE Author 1 Author 2 Name: S. Ramamurthy Name: Drishya G Designation: Director (G), Geodata Division Geological Survey of India, Eastern Region, Saltlake, Kolkata. Designation: Geologist, Opn: West Bengal & Andaman Geological Survey of India, Eastern Region, Saltlake, Kolkata. Work Experience: Associated with Geological mapping and mineral exploration in parts of Chattisgarh, Tripura and Mizoram, Andhra Pradesh for two decades Associated with the applications of Geoinformtics in earth sciences and imparting training in Geoinformatics over a decade. Work Experience: Associated with National Geochemical Mapping for two years 6 P a g e