Remote sensing applications primarily involves interpretation and analysis of electromagnetic radiations interacting with earth and its atmosphere utilising data collected by earth observation (EO) sensors on-board aerial or satellite platforms. The EO system with its ability for a synoptic view, repetitive observations at different spatial, spectral and radiometric resolutions has been widely accepted as an indispensable tool for natural resources inventory, monitoring, generating data for resource management planning, weather forecast, disaster damage assessment and climate change studies. The Indian Earth Observation Programme has been applications driven and contribution to national development has been its prime motivation. India’s EO capability has increased manifold since the launch of experimental satellite Bhaskara-I in 1979 to the recent launches of RISAT-1 in April 2012, Saral AltiKa in March 2013 and INSAT-3D in July 2013. The improvements in observation capabilities are not only in spatial, spectral, temporal and radiometric resolutions, but also in their global coverage as well as value-added products.
EO data has been extensively used in a number of earth science applications for societal benefits; and studies have been carried out at Space Applications Centre (SAC), Ahmedabad, involving scientific teams from institutions specialising in various fields of applications. Many of the projects have been sponsored by Ministry of Environment and Forests, Ministry of Water Resources and have been carried out in collaboration with Ministry of Earth Sciences. This article provides a glimpse of such work.
Remote Sensing Applications in Earth Sciences
Monitoring Snow and Glaciers of Himalayas: Remote sensing applications and GIS based techniques along with field expeditions have been developed to map and monitor snow and glaciers of the Himalayas. Glacier inventory was carried out for the Indus, the Ganga and the Brahmaputra river basins on 1:50,000 scale using images of Indian remote sensing satellite for the period 2004-2007 and a database has been prepared in a geographic information system (GIS) environment. Fig 1 shows typical glacier features like accumulation area, ablation zone, snow line, snout, glacier lake in Himalayan glaciated terrain as seen on IRS LISS-IV FCC image. The study has shown that there are 32392 glaciers covering 71182 sq. km area in the Himalayan region. Normalised Difference Snow Index (NDSI) algorithm was developed using AWiFS data and continuous monitoring of snow cover of the entire Himalayan region at basin and sub-basin level is being carried out since the year 2004 at 10 day intervals by generating snow cover maps, carrying out area estimates and analysing the data. Glacier retreat/advancement has been monitored using temporal satellite images. Monitoring of ~1800 glaciers in various parts of the Himalaya has indicated 17 per cent loss in glaciated area for the 1962-2001 time frame. It is also observed that ~2 per cent loss in glaciated area has occurred for ~480 glaciers monitored using satellite images from 1990 to 2001. Further it is also observed that for ~2000 glaciers monitored using satellite data of 2001-2011 time frame, there is < 0.2 per cent loss in glaciated area and 87 per cent of glaciers are observed to be stable. Techniques have been developed to estimate glacier mass balance. The results are being utilised to understand the variability and effect of changing climate on snow and glaciers, estimating the snow melt runoff and hydropower potential for selected watersheds in the Himalayan region.
Desertification Status Inventory: Desertification is the process of land degradation in arid, semi-arid and dry-sub-humid areas. Desertification and land degradation status mapping has been carried out for the entire country on 1:500,000 scale using the AWiFS data. The dominant processes of land degradation, viz. water erosion, vegetal degradation, wind erosion, salinisation/alkalisation, water logging, frost heaving, frost shattering, mass movement, etc. have been deciphered and mapped using satellite data. The study reveals that 105.48 m ha area of the country is undergoing processes of land degradation (32.07 per cent of the total geographic area of the country). Area undergoing desertification is 81.4 m ha. Updation of desertification status maps has been taken up using recent satellite data sets.
National Wetland Inventory: Conservation and wise use of wetlands has been given priority world over. India harbours diverse types of wetlands. National-level inventory and assessment of wetlands has been carried out using Resourcesat-1 LISS-III data of 2006–07 at 1:50,000 scale. A hierarchical system comprising 19 classes based on Ramsar definition has been used to classify the wetlands of India. The extent of wetlands has been estimated to be 15.26 m ha. Inland wetlands account for 69.22 per cent (10.564 m ha), whereas the coastal wetlands account for 27.13 per cent (4.14 m ha). The high-altitude wetlands (situated > 3000 m asl) in the Himalayan states were also mapped, comprising 126,249 ha of areal extent. The status of wetlands in terms of water spread, turbidity of open water and aquatic vegetation has shown significant variation during pre- and post-monsoon seasons.
Monitoring Indian Coastal Zone: Indian coast has been monitored using EO satellites for last three decades. Under these studies, methodologies have been evolved to study the coast using satellite data, generate baseline data, map the critical and vital habitats (coral reefs and mangroves), etc. Recently coastal landuse maps showing ecologically sensitive areas (ESAs) and high tide and low tide lines on 1:25, 000 scale using LISS-IV data of 2004-06 have been prepared and put in GIS mode. Coastal Zone Information System (CZIS) has been developed which includes baseline thematic data generated so far for all the maritime states and union territories of India. Shoreline change mapping of the entire Indian coast on 1:25,000 scale using satellite data of 1989-91 and 2004-06 time frame is completed and an atlas has been prepared showing areas under erosion and accretion and status of coastal protection works in an GIS environment. The coastal thematic information derived from EO satellites and put in GIS environment as CZIS is widely utilised for several applications such as zoning the coast, based on Coastal Regulation Zone (CRZ) or Coastal Management Zone (CMZ) and in particular identifying ecologically sensitive areas, monitoring implementation of CRZ, site selection of mangroves and shelter belts, conservation of coral reefs and mangroves, site selection of any developmental activities, identification of eroding coast, understanding coastal processes, understanding the role of keystone coastal ecosystems in global climate change and identifying vulnerable zones due to predicted sea level rise etc.
Marine Lithosphere: Gravity, geoid and magnetic data provide the unique opportunity of seeing below water and thick sediments to understand the structure and dynamics of the Indian Ocean lithosphere. Altimeter derived geoid undulation and free-air gravity anomalies over oceans are important data to understand plate tectonic processes relating to oceanic ridges, subduction zones, formation of marine sedimentary basins and the evolution of continental margins. Geoid-topography and gravity anomaly-topography relations in spectral domain have been used to understand long-term mechanical properties of oceanic lithosphere under seamounts, oceanic ridges, fracture zones and subduction zones.
Techniques for the retrieval of geoid and gravity anomaly data from satellite altimetry and generate improved high resolution (1´×1´) geoid and gravity anomaly maps (accuracy~5 to 7 m Gal) of the northern Indian Ocean have been developed (Fig 2). Further, the geoid and gravity data have been utilised to understand the deep structure and evolution of Indian Ocean lithosphere and associated geodynamics. SAC is currently working towards further improvements in the geoid and gravity retrieval using Saral AltiKa data.
Early Warning of Disasters: Research and development activities related to developing techniques for early warning of some of the disasters under Disaster Management Support Programme (DMSP) of Department of Space have been taken up. Real-time cyclone track prediction algorithms using INSAT data have been developed and predicted in real-time with a lead time of 48 hours. Prediction of cyclone track and landfall has been made operational and technology has been transferred to India Meteorological Department (IMD). Technique was developed to detect cyclogenesis over the Indian Ocean based on pattern matching and use of OSCAT winds; and for automated estimation of cyclone position and intensity using INSAT imager data. An operational web-server ‘SCORPIO’, for real time monitoring and prediction of cyclones is developed.
Early warning research towards identification of precursors to earthquakes has been taken up. Earthquake precursors such as sudden rise in land surface temperature, crustal deformation changes, ionospheric perturbations have been studied for selected seismically active regions. Methodology for assessing coastal vulnerability to storm surges and tsunami are developed and demonstrated for Andhra Pradesh and Tamil Nadu coasts. Rainfall threshold based early warning models of landslides in Sikkim Himalayas have been developed.
For geospatial data generation and dissemination SAC has been analysing EO data from a host of sensors (e.g., hyperspectral spectrometers, altimeters, scatterometers, radiometers, imagers, sounders, synthetic aperture radars) along with a large number of partner institutes and generating geophysical and bio-physical data products useful for understanding and modelling various earth system science applications. This has led to demonstration of newer applications as well capacity building in the country.
Meteorological and Oceanographic Satellite Data Archival Centre (MOSDAC) is established by SAC as a single window interface (www.mosdac.gov.in) to provide satellite and in-situ data and value added products to the scientific community in the fields of meteorology and oceanography and earth sciences for their research work.
Remote Sensing Applications – Way Forward
In order to cater to the needs of societal applications there is requirement for development of new sensors as well as run a continuity in the existing missions. A constellation of satellites is required for early warning of disasters. The new EO systems planned for launch in the near future are GISAT and INSAT-3D(R) missions. The need of the hour is to work on process models considering Earth as an integrated system. The concept of Earth System Science needs to be strengthened and space based observations needs to be integrated with numerical process models. The inter-institutional partnership has been developed as a part of work carried out so far, it will enable such an effort.