Dr Saumitra Mukherjee
Professor & Head (Geology & Remote Sensing)
School of Environmental Sciences
Geospatial technology has proved to be a part of mainstream business and management operations around the world in several organisations as diverse as cities, state government, utilities, telecommunications, railroads, civil engineering, petroleum exploration, retailing, etc. This array of institutional types is integrating geospatial technology into their daily operations. The applications associated with these systems are equally broad from infrastructure management to vehicle routing, to site selection, and research and analysis. This technology is also facilitating environmental restoration, resource management, habitat analyses, environmental change detection, aquatic plant tracking, historical preservation, hydrology and hydraulics, channel/inland waterways maintenance, emergency response, flood plain mapping, real estate/ cadastral, master planning, district/ construction management, socio-economic analysis and atmospheric/ geologic/ geomorphic analysis for earthquake and related hazard assessment/prediction. In general, the market is looking now at geospatial technology as a supportive means to improve / optimise business processes.
Investing in geospatial technology, just to have a new technology on board is a concept of the past. Also, strange calculations of ROI or TCO for implementation of this technology are now being seen as something very artificial. The real advantage of geospatial science lies in its enormous capability to improve business processes and that’s the reason the profitability of this tool has to be always estimated in conjunction with business improvement / optimisation.
Remote sensing and GIS applications in water resource management
The land use of Delhi has undergone drastic change. Change in land use, population growth and seismic instability have all contributed in changing the hydrogeomorphology of the urban sprawl of the city.
In order to understand the capability of remote sensing and GIS in addressing the ecological crisis, study was carried out to examine hard rocks, colluvial and alluvial aggregates for exploration, exploitation and management of water resources. It required a geo-scientific database of water resources for generation of development plans for optimal use of potential resources. To achieve a systematic approach to understanding the terrain characteristic at a regional level, a detailed mapping was done by using geological, geophysical, drilling and analysis of drill cuttings and groundwater samples. Remote sensing and GIS were used here which have emerged as the most optimal means for monitoring and management of water resources on global, regional and local scale. Being at higher elevation of NCR region with conditions like fault zones, groundwater bearing fracture system and buried pediment plains, major part of the study area has become ideal recharge zone for better groundwater conditions. At higher elevations, drainage system which follows the structural lineament and fault zone, limit the capacity to hold and retain surface runoff of the rainwater.
Drilling was carried out in Aravalli in seven locations in Jawaharlal Nehru University (JNU) and four locations in Research and Referral Hospital. Information from the drilled litholog was correlated with resistivity, magnetic and attributes of NDVI (Normalized Difference Vegetation Index) from satellite data. Analysis of drilled logs and groundwater samples from different zones was done to correlate these data with remote sensing geological and geophysical information. The data along with ancillary information was analysed in Arc/GIS software for attribute data creation, derivation of secondary maps of groundwater prospects and quality zonation.
For the present investigation, satellite data was taken from IRS 1C, IRS 1D (LISS III), Resourcesat and Landsat. For geo-referencing, Survey of India toposheet and NATMO maps were used. The data collected from different sources was used as ground truth information for preparation of various thematic maps. Detailed ground truthing has been carried out in some selected areas of study. The ground truthing includes resistivity and magnetic surveys and drilling by Down the Hole Hammering (DTH) rig. The process involved following steps:
- Interpretation of data available (geophysical, geological, geochemical, soil texture and drilling) for locating suitable groundwater exploration points.
- Interpretation of IRS, Resourcesat, SPOT, and Landsat data for demarcation of groundwater zone including its quality.
- Digital Elevation Model generated Shuttle Radar Terrain Mission (SRTM) were used to identify the structural control of an area.
- Interpretation of lineament and fracture system in the NCR region.
- Collection of samples for detailed geochemical and petrological analysis.
- Confirmation of recently identified groundwater zone based on distinct vegetation anomaly and lineament fabrics depicted on satellite images.
- Identification of possible groundwater zones based on drilling data.
- Identification of groundwater quality based on NDVI attributes.
Remote sensing and GIS: Remote sensing has been found to be very useful in this study. These tools and techniques were useful for water resource management in the following ways.
- Homogenisation of data – This enabled to bring all the old and new data on common platform and on uniform scale. This uniformity of scale is the prime need for any analysis on one common platform. In this process entire data has been organised in the common projection system, scale and on common GIS format.
- Updation of information by using remote sensing, field verification and laboratory analysis. The information has been updated and correlated with each other.
Field Observation: The interconnected fracture in Aravalli quartzite was found to have potential for groundwater exploration. Within Aravalli quartzite, the ferruginous variety was found to be more fracture prone. Pegmatite, aplite and quartz vein intercalated with schistose rocks have multiple fracture system. Thin section analysis of rocks from different depth zones showed that the grade of metamorphism has relevance with groundwater quality and potentiality. It was observed that from Aravalli quartzite to river Yamuna, there are three prominent watershed boundaries in existence. The buried pediment plains and alluvial plain boundary is demarcated by a very thick layer of fine grained sediments. Hydrogeomorphologically this boundary is not suitable for groundwater exploration. Elemental composition (rock analysis) of the selected rock samples were analysed by ICPAES. The rock sample represents potential fracture zones encountered during groundwater exploration. The analytical data revealed the following features:
- In all drilling sites, silica content increased with depth which is suggestive of good to excellent groundwater quality at depth.
- Concentration of Al2O3 decreased with depth which is also suggestive of excellent groundwater quality.
- Concentration of Zirconium (Zr) was found higher in upper zone (245ppm) and reduced to bare (20ppm) at greater depth which suggests that emplacement of pegmatities are near the surface and is overlying on fractured quartzite at greater depth.
The conclusions inferred from the research work suggested that wherever the lineament density was high, there was resistivity and magnetic anomaly with lower values. At all these places, groundwater available is in large quantity. If NDVI is high, the vegetation is thick due to high moisture laden lineament which is suggestive of high mineral availability and hence, the availability of groundwater. Wherever there has been excessive use of land, it is difficult to find out the contours of the lineaments. However the lineaments of the unperturbed lands can easily be determined. Resistivity survey threw light on different levels of availability of water. One could infer from photomicrograph of rock shreds obtained during drilling that high grade metamorphism has not disturbed the aquifers. Since all the aquifers are situated at great depth, they are beyond anthropogenic perturbations. On the other hand, alluvial aquifers are more prone to anthropogenic pollution as they are shallow and therefore not potable. Further, it was found that wherever there has been change in the land use, the natural recharge potential has also declined. DEM tells us the course of water run-off and that can help in recharging the aquifer. The study also concluded that wells may not be directly recharged. There can be indirect method of recharging them. Recharging the lateral dry wells can be done by the lateral homogeneity.
In our total area of study at JNU which is approximately 5sqkm, the number of tube wells were restricted to seven based on the delineation of micro-watershed. As per the National Water Policy, there should not be more than one tube well in one micro-watershed. The research work concluded that there should not be further drilling in JNU for sustainable performance of the aquifers. Although the discharge of the tube wells range from 24,475Lt/hr to 34,125Lt/hr with less than 10mts draw down in 72hrs of pumping, it is recommended that groundwater should be pumped from tube wells for 8 hrs and then it should be allowed to recover for the next 5 hrs. In this area, most of the drilling site fractures are interconnected with high transmissibility, and it has been observed that 80 per cent recovery of draw down takes place within 1hr, if surrounding tube wells are also stopped. Remaining 20 per cent recovery takes 4hrs due to elastic nature of the aquifer. Hence, it would be safer if the tube wells are not pumped together with more than 8hrs.
Similar work was carried out from Remote Sensing Laboratory, SES, JNU in Humanyun Tomb, IGNOU and Research and Referral Hospital areas. Based on the study, it was possible to identify suitable location for water resource management in the whole of Delhi. It was calculated that the cost of satellite data and other GIS layer generation is more scientific and cost effective for a large area. However, it is essential to generate and analyse the data by qualified and experienced scientists and engineers only.
Remote sensing and GIS applications in early warning of natural hazards
A sudden l drop in Kp and electron flux is an indication of atmospheric disturbance before occurrence of earthquakes in earthquake prone areas. This hypothesis was supported by the event of erratic rainfall and snowfall before earthquake in India-Pakistan border on October 8, 2005. Due to low electron flux, the local drop in temperature in the upper part of atmosphere leads to condensation of clouds on the affected part of the earth. Further, on December 25, 2004 and February 23, 2005, hailstorms and snowstorms were reported in the northern hemisphere, while in the tropics a sudden drop in temperature led to foggy and smoggy conditions. An earthquake measuring 9.0 of Richter scale on 26 December followed the sudden changes in the environment. An earthquake measuring 6.4 on the Richter scale occurred on 22 February in Zarand, Kerman Province (750 KM south-east of Tehran) at 05:55 local time. Weather condition in this region was bad as there had been heavy snowfall, resulting in a number of road blockades.
There is a theoretical correlation between starbursts, solar minimum, sun-earth environment, snowfall and earthquake. The permanent component of cosmic radiation comes from the galaxy. It consists of very highly charged particles ejected by the gigantic explosions of supernova, massive stars that have reached the end of their days. These particles are atoms, which have been stripped of their electrons because of the temperatures within these giant stars. We see that during periods of high solar activity, the cosmic radiation is less intense, as the cosmic effect suppresses the formation of sunspots. When cosmic rays come in contact with the atmosphere of the Earth, ionisation takes place. During this ionisation, thermal energy is utilised to produce a regional fall in the temperature of the earth, which may lead to sudden snowfall in higher latitude and altitudes of the planet. The magnetic field around the Earth protects the planet from cosmic rays. This field is stronger when Sun is more active, that is, emitting more ultraviolet radiation and displaying more sunspots. During this time, fewer cosmic rays can penetrate Earth’s atmosphere. A direct influence of cosmic rays with the fall in temperature was observed during the years of starburst. A correlation between the global average of low cloud cover and the flux of Galactic cosmic rays (GCRs) in the atmosphere has been observed. International Satellite Cloud Climatology Project (ISCCP) and ground based diffuse solar radiation data provide a new evidence for a non-linear effect of GCRs on environment of the earth. It has been observed that during Forbush events, simultaneous decrease occurs in the diffuse fraction. Thus, it is possible to correlate cosmic ray variations with geomagnetic storms, which changes the ionospheric currents and triggers seismic activities in earthquake prone areas. ROI and TCO of early warning are not calculated so far; however it is important to note that terrestrial as well as extraterrestrial satellite data along with the GIS attribute changes, in geocoordinate specific PIXEL changes, can be done on global scale. The potential of the change detection in atmospheric and geospheric level has a very promising impact on the geospatial technology in corporate sector.