Current Science

S. K. Singh ¹, A. S. Rajawat ¹, B. P. Rathore ¹, I. M. Bahuguna ¹, M. Chakraborty ¹

Affiliations
1 Geo Science and Applications Group, Space Applications Centre (ISRO), Ahmedabad 380 015, IN

Abstract

Synthetic aperture radar (SAR) signals penetrate through the dry snow and cloud providing crucial data over the Himalayan temperate glaciers and complement the optical images. In the present study, RISAT-1 C band and AWiFS images of winter/ablation period over Samudra Tapu and Gepang Gath moraine dammed lakes (MDLs) in Himachal Pradesh have been analysed. Backscattering coefficient of the lake was observed to be low throughout the year. Penetration depth of SAR into dry snowpack was calculated to vary from 4 to 22 m for a range of snow density (0.1-0.5 g/cm³), whereas it was estimated to be 1.20- 2.01 m based on ground observations for 30 January and 24 February 2013. The present study provides results of RISAT-1 C-band penetration up to ~2 m through the snowpack to detect MDLs in the Himalayan terrain. The detection of MDLs using the backscattering images of winter season was validated with synchronous AWiFS sensor images.

Keywords

Backscattering Coefficient, Glacier Lakes, Snow and Cloud, Synthetic Aperature Radar.

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B. P. Rathore ¹, S. K. Singh ¹, Rupal Brahmbhatt ², I. M. Bahuguna ¹, A. S. Rajawat ¹, Ajai ¹

Affiliations
1 Space Applications Centre (ISRO), Ahmedabad 380 015, IN
2 M. G. Science Institute, Ahmedabad 380 009, IN

Abstract

Monitoring of lakes in glaciated terrain in the Himalayan region has been recognized as one of the priority areas especially after the Kedarnath disaster. Among all types of glacial lakes, moraine dammed lakes (MDLs) are the most important from disaster point of view. Remote sensing plays a significant role in view of availability of unbiased repeated data on the expansion or contraction of MDLs located in rugged terrains of the Himalaya. Monitoring of two MDLs, associated with Katkar and Gepang-gath glaciers in Zanskar and Chandra sub-basins respectively was done using satellite images of 1965, 1976, 1989, 2001, 2006-07, 2012 and 2014. Survey of India (SOI) topographical maps of 1962 were also referred to monitor the respective glaciers lakes. SOI maps show the presence of only one lake associated with Gepang-gath glacier. Areal extent of the MDLs had increased from 21 to 57 ha between 1965 and 2014, and from 27 to 80 ha between 1962 and 2014 for the Katkar and Gepang-gath glaciers respectively. Increase in peak discharge of the two lakes was also estimated using different empirical models in case of outbursts of these lakes. The lake outburst probability for both these lakes was found to be very low (less than 1%), however, possibility of outburst of lakes due to natural calamity like cloud burst, landslide or earthquake cannot be ignored. The rate of retreat of these two glaciers was observed to be high due to the presence of MDLs in comparison to surrounding glaciers in the valley.

Keywords

Glacier, Moraine Dammed Lake, Peak Discharge, Retreat.

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A. S. Rajawat ¹, H. B. Chauhan ¹, R. Ratheesh ¹, S. Rode ¹, R. J. Bhanderi ¹, M. Mahapatra ¹, Mohit Kumar ¹, R. Yadav ², S. P. Abraham ³, S. S. Singh ², K. N. Keshri ², Ajai ¹

Affiliations
1 Space Applications Centre, Indian Space Research Organisation, Ahmedabad 380 015, IN
2 Central Water Commission, Ministry of Water Resources, New Delhi 110 606, IN
3 Central Water Commission, Ministry of Water Resources, Kochi 682 020, IN

Abstract

The long stretch of coastline on either side of the Indian peninsula is subjected to varied coastal processes and anthropogenic pressures, which makes the coast vulnerable to erosion. There is no systematic inventory of shoreline changes occurring along the entire Indian coast on 1 : 25,000 scale, which is required for planning measures to be taken up for protecting the coast at the national level. It is in this context that shoreline change mapping on 1 : 25,000 scale for the entire Indian coast based on multidate satellite data in GIS environment has been carried out for 1989-1991 and 2004-2006 time frame. The present communication discusses salient observations and results from the shoreline change inventory. The results show that 3829 km (45.5%) of the coast is under erosion, 3004 km (35.7%) is getting accreted, while 1581 km (18.8%) of the coast is more or less stable in nature. Highest percentage of shoreline under erosion is in the Nicobar Islands (88.7), while the percentage of accreting coastline is highest for Tamil Nadu (62.3) and Goa has the highest percentage of stable shoreline (52.4). The analysis shows that the Indian coast has lost a net area of about 73 sq. km during 1989-1991 and 2004-2006 time frame. In Tamil Nadu, a net area of about 25.45 sq. km has increased due to accretion, while along the Nicobar Islands about 93.95 sq. km is lost due to erosion. The inventory has been used to prepare a Shoreline Change Atlas of the Indian Coast.

Keywords

Accretion, Coastal Erosion, Shoreline Changes, High and Low Tide Lines, Satellite Data.

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B. P. Rathore ¹, S. K. Singh ¹, I. M. Bahuguna ¹, R. M. Brahmbhatt ², A. S. Rajawat ¹, A. Thapliyal ³, A. Panwar ³, Ajai ¹

Affiliations
1 Space Applications Centre (ISRO), Ahmedabad 380 015, IN
2 M.G. Science Institute, Ahmedabad 380 009, IN
3 Uttarakhand Space Application Centre, Dehradun 248 006, IN

Abstract

Advance wide field sensor (AWiFS) data of RESOURCESAT-1 and 2 satellites of IRS series were used to produce snow cover products at 10-day interval from 2004 to 2012 covering October to June of consecutive years for Alaknanda, Bhagirathi and Yamuna sub-basins of Ganga basin in the Himalayan region. The snow products were generated using Normalized Difference Snow Index (NDSI) at a spatial resolution of 56 m using green (B2) and SWIR (B5) channels of AWiFS sensor. Minimum and maximum snow cover was found to be 998, 669, 141 sq. km, and 7874, 5876, 3068 sq. km for Alaknanda, Bhagirathi and Yamuna sub-basins respectively. The areal extent of snow was higher than the mean during the years 2004-2005, 2007-2008 and 2011-2012 for all sub-basins. Mean of monthly fluctuations between maximum and minimum snow cover were recorded as 3105, 2305, 1235 sq. km corresponding to variation in snow line altitude of 1613, 1770, 1440 m respectively. A subtle increase in the snow cover has been observed in these three sub-basins during 2004-2012. The results matched well with the variations in temperature taken from nearby ground weather stations. Snow cover products were analysed to understand spatio-temporal variability of accumulation and ablation of snow in the three sub-basins. Monthly fluctuations in snow cover were high during accumulation period than in ablation. This work also attributes in generation of long-term database which will be useful for understanding climatic variations over Himalayan region.

Keywords

Ablation, AWiFS, Ganga, NDSI, Snow Cover.

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K. M. Sreejith ¹, P. S. Sunil ², Ritesh Agrawal ¹, D. S. Ramesh ², A. S. Rajawat ¹

Affiliations
1 Geosciences Division, Space Applications Centre (ISRO), Ahmedabad 380 015, IN
2 Indian Institute of Geomagnetism (DST), Navi Mumbai 410 218, IN

Abstract

We present InSAR observations of the co-seismic deformation caused by the Mw 7.8 Gorkha, Nepal earthquake. Analysis of Sentinel-1 data revealed about 100 x 100 sq. km surface deformation with ~1 m upliftment near Kathmandu, and ~0.8 m subsidence towards north along the line of sight of the satellite. The maximum deformation is observed about 40 km east-southeast of the epicentre, suggesting eastward propagation of the rupture. Elastic dislocation modelling revealed that the overall rupture occurred on a 170 km long, 60 km wide fault along the strike (286°) and dipping north (dip = 15°) with large amount of slip (4.5 m) confined to the centre (95 x 22 sq. km) and less slip (0.25 m) on the surrounding part of the fault plane. The corresponding moment magnitude is M_w 7.75. The area, depth and dip of the modelled fault plane are fairly consistent and overlap with the location of mid-crustal ramp in the Main Himalayan Thrust. We infer that the earthquake was possibly caused by the release of inter-seismic strain energy accumulated in the environs of mid-crustal ramp due to plate boundary forces.

Keywords

Co-Seismic Deformation, Gorkha, Nepal Earthquake, Synthetic Aperture Radar Interferometry, Source Model.

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Hrishikesh Kumar ¹, A. S. Rajawat ¹

Affiliations
1 Space Applications Centre, Indian Space Research Organisation, Ahmedabad 380 015, IN

Abstract

In the present study, we have demonstrated the potential of RISAT-1 Synthetic Aperture Radar (SAR) data to detect palaeochannels in parts of Thar Desert, India, which may be utilized as one of the guides of geoarchaeological exploration, besides forming groundwater prospective zones. Palaeochannels have been detected using RISAT-1 SAR MRS datasets in the southern parts of Jaisalmer and northeastern parts of Barmer districts, Rajasthan. These palaeochannels of length varying between 14 and 36 km and width varying between 20 and 65 m are present within parabolic sand dune complexes. Palaeochannels have been detected as distinct dark tone on RISAT-1 SAR data compared to feeble expression on corresponding LANDSAT-OLI FCC datasets. This is due to sand-filled valleys, acting as radar smooth surface and absorbing the radar energy with negligible backscatter and enhanced topography due to side-looking capability of RISAT-1 SAR. High-resolution Cartosat DEM has been utilized to prepare topographical profiles, supporting the geomorphological interpretation. Merging of RISAT-1 SAR and LANDSAT ETM datasets using PCA techniques led to enhancements of palaeochannels on merged FCC data products. Like polarization of RISAT-1, SAR data could further enhance and aid in detecting palaeochannels. The entire region was flooded in August 2006 and water had flown through these palaeochannels, which subsequently dried up and facilitated their easy detection; they are otherwise difficult to interpret using pre-flood images. Analysis of sequential post-flood images has been taken up for detailed study of the area, as there is scope to detect additional hitherto unknown palaeochannels.

Keywords

Desert, Geoarchaeological Exploration, Palaeochannels, Synthetic Aperture Radar Data.

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B. P. Rathore ¹, I. M. Bahuguna ¹, S. K. Singh ¹, R. M. Brahmbhatt ², S. S. Randhawa ³, P. Jani ⁴, S. K. S. Yadav ⁵, A. S. Rajawat ¹

Affiliations
1 Space Applications Centre (ISRO), Ahmedabad 380 015, IN
2 M. G. Science Institute, Ahmedabad 380 009, IN
3 State Centre on Climate Change, SCSTE, Shimla 171 009, IN
4 CEPT University, Ahmedabad 380 009, IN
5 Remote Sensing Applications Centre, Lucknow 226 021, IN

Abstract

The extent of snow cover on the earth is considered an important parameter for numerous climatological and hydrological applications. Snow cover dynamics in mountainous regions is a vital input for energy balance, glacier mass balance, climate change and snowmelt runoff modelling. There have been global efforts for monitoring of snow cover of earth at varying spatial and temporal scales by generation of snow products. Among these, one of the high temporal and spatial resolution datasets has been generated using advanced wide field sensor data for Western and West-Central Himalayan region at the Space Applications Centre, Ahmedabad. This is done using an algorithm developed based on normalized difference snow index. This paper discusses the trends of snow cover from 2004 to 2014 based on an input of approximately 12,600 snow cover products at sub-basin scale in Indus, Chenab, Satluj and Ganga basins. Analysis of snow cover shows high variability during accumulation than in ablation period. A subtle increase in snow cover was observed in all basins during 2004–2014.

Keywords

Ablation, Accumulation, AWiFS, Snow Cover, NDSI, Western and West-Central Himalaya.

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Hiren Bhatti ¹, Ratheesh Ramakrishnan ¹, A. K. Sharma ¹, A. S. Rajawat ¹

Affiliations
1 Space Applications Centre, Jodhpur Tekra, Ahmedabad 380 015, IN

Abstract

Extensive erosion of high tidal mudflat along the northern parts of Gulf of Khambhat (GoK) was observed from the analysis of time series satellite images during the time period from March 2014 to September 2017. Around 28.66 sq. km area of high tidal mudflat eroded within this time period. Maximum erosion rates estimated have even peaked to about 4 km/year showing the severity of erosion. The mudflats under erosion are along the outer boundary of a meandering tidal channel connecting the Gulf with Mahi river. A possible cause of the incessant erosion of mudflats is the strong tidal currents along the outer boundary of the meandering tidal channel, that have carved the mudflats and pushed the tidal channel further landward. A subtle seasonal pattern of erosion was observed with decrease in erosion rates during the summer monsoon period when the high tidal currents are weak due to the river influx. Rapid erosion of the tidal mudflats has not only destroyed the vital habitat, but has also eventually exposed the inhabited land area to tidal flooding, making it vulnerable to erosion. The study shows the importance of assessing the stability of mudflats along the GoK, where large development activities are proposed.

Keywords

DSAS, Erosion, High Tidal Mudflat, Satellite Data, Tidal Channel.

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S. Dharumarajan ¹, M. Lalitha ¹, Rajendra Hegde ¹, N. Janani ¹, A. S. Rajawat ², K. L. N. Sastry ², S. K. Singh ³

Affiliations
1 ICAR-National Bureau of Soil Survey and Land Use Planning, Hebbal, Bengaluru - 560 024, IN
2 ISRO-Space Applications Centre, Ahmedabad - 380 015, IN
3 ICAR-National Bureau of Soil Survey and Land Use Planning, Amaravati Road, Nagpur - 440 033, IN

Abstract

Desertification is the transformation of productive land into a non-productive one due to poor resource management, and unfavourable biophysical and economical factors. Periodical assessment of desertification status is imperative for a suitable comprehensive and combating plan. In the present study, desertification status maps of Andhra Pradesh (AP), Karnataka and Telangana in South India have been prepared using remote sensing data for two time-frames (2003– 2005 and 2011–2013) and change detection analysis has been carried out. The results reveal that 14.35%, 36.24% and 31.40% of the total geographical area in Andhra Pradesh, Karnataka and Telangana were affected by desertification processes respectively, in 2011–2013. Among the desertification processes, vegetal degradation contributes 7.27% of total area in AP, followed by water erosion (4.93%) and waterlogging (0.83%), whereas in Karnataka water erosion (26.29%) is dominant followed by vegetal degradation (8.93%) and salinization (0.45%). Change detection analysis shows that desertification processes of AP and Karnataka have increased by 0.19% and 0.05% respectively, whereas in Telangana it has decreased by about 0.52% from 2003 to 2005 data. The present database will help the scientists, planners and stakeholders to prepare appropriate land reclamation measures to control the increasing trend of desertification.

Keywords

Change Detection Analysis, Desertification, Salinization, Vegetal Degradation, Waterlogging.

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Satadru Bhattacharya ¹, Hrishikesh Kumar ¹, Arindam Guha ², Aditya K. Dagar ¹, Sumit Pathak ¹, Komal Rani (Pasricha) ², S. Mondal ³, K. Vinod Kumar ², William Farrand ⁴, Snehamoy Chatterjee ⁵, S. Ravi ⁶, A. K. Sharma ¹, A. S. Rajawat ¹

Affiliations
1 Space Applications Centre, Indian Space Research Organisation, Ahmedabad 380 015, IN
2 National Remote Sensing Centre, Indian Space Research Organisation, Hyderabad 500 042, IN
3 Department of Geophysics, Indian Institute of Technology (ISM), Dhanbad 826 004, IN
4 Space Science Institute, Boulder, Colorado 80301, US
5 Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, Michigan 49931, US
6 Geological Survey of India Training Institute, Bandlaguda, Hyderabad 500 068, US

Abstract

In this article, we discuss the potential of airborne hyperspectral data in mapping host rocks of mineral deposits and surface signatures of mineralization using AVIRIS-NG data of a few important geological provinces in India. We present the initial results from the study sites covering parts of northwest India, as well as the Sittampundi Layered Complex (SLC) of Tamil Nadu and the Wajrakarur Kimberlite Field (WKF) of Andhra Pradesh from southern India. Modified spectral summary parameters, originally designed for MRO-CRISM data analysis, have been implemented on AVIRIS-NG mosaic of Jahazpur, Rajasthan for the automatic detection of phyllosilicates, carbonates and Fe–Mg-silicates. Spectral analysis over Ambaji and the surrounding areas indicates the presence of calcite across much of the study area with kaolinite occurring as well in the north and east of the study area. The deepest absorption features at around 2.20 and 2.32 μm and integrated band depth were used to identify and map the spatial distribution of phyllosilicates and carbonates. Suitable thresholds of band depths were applied to map prospective zones for marble exploration. The data over SLC showed potential of AVIRIS-NG hyperspectral data in detecting mafic cumulates and chromitites. We also have demonstrated the potential of AVIRIS-NG data in detecting kimberlite pipe exposures in parts of WKF.

Keywords

Data, Geological Provinces, Host Rocks, Hyperspectral, Mineral Deposits.

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R. Ratheesh ¹, Nandini Ray Chaudhury ¹, Preeti Rajput ¹, Mohit Arora ¹, Ashwin Gujrati ¹, S. V. V. Arunkumar ¹, Ateeth Shetty ², Rakesh Baral ³, Rakesh Patel ⁴, Devanshi Joshi ⁴, Harshad Patel ⁴, Bharat Pathak ⁴, K. S. Jayappa ², R. N. Samal ³, A. S. Rajawat ¹

Affiliations
1 Space Applications Centre, Indian Space Research Organisation, Ahmedabad 380 015, IN
2 Mangalore University, Mangalagangorti, Mangaluru 574 199, IN
3 Chilika Development Authority, Bhubaneswar 751 014, IN
4 Gujarat Ecological Education and Research Foundation, Gandhinagar 382 007, IN

Abstract

This article highlights major scientific outcomes of the studies carried out using Airborne Visible/Infrared Imaging Spectrometer-Next Generation (AVIRIS-NG) airborne data over the coastal regions of Mangaluru, Gulf of Kachchh (GoK) and Chilika lagoon. Various hyperspectral remote sensing techniques involving bio-optical models and spectral classification algorithms are used to achieve different objectives related to coastal ecosystem monitoring. AVIRIS-NG airborne data are used to estimate particle size of suspended solids along the coastal waters of Mangaluru using an analytical optical model. The spatial distribution of particle size of the suspended solids in the coastal waters is brought out, while along the coastal land of Mangaluru, the beaches are classified based on uniform sediment characteristics using spectral matching algorithm. AVIRIS-NG data for Pirotan reef in GoK is analysed and species-level identification of the dominant brown macroalgae is carried out. Species-level distribution of brown macroalgae is mapped and used to study the microhabitat preference of different species. At Chilika lagoon, the AVIRIS-NG data are analysed to map the abundance of submerged seagrass using bio-optical model, which provides vital information to the coastal management community. The study asserts the importance of hyperspectral data and various advanced data analysis techniques related to the estimation of geophysical parameters of the coastal waters and monitoring the vital coastal ecosystems.

Keywords

Brown Macroalgae, Coastal Regions, Suspended Sediment Properties, Submerged Seagrass.

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R. P. Singh ¹, Shard Chander ¹, Ratheesh Ramakrishnan ¹, Ashwin Gujrati ¹, Rohit Pradhan ¹, Chirag Wadhwa ¹, A. S. Rajawat ¹, Raj Kumar ¹

Affiliations
1 Space Applications Centre, Indian Space Research Organisation, Ahmedabad 380 015, IN

Abstract

In this study we identify a region of submarine groundwater discharge (SGD) near Okha coast, Gujarat, India using thermal infrared remote sensing technique. Observations of brightness temperature (BT) in the thermal infrared spectral region (10.6–11.19 μm) from Landsat-8 satellite in the coastal region showed unique localized cooling in the Arabian Sea during winter. We observed lowering of BT in the range 0.6°– 2.3°C in the coastal region associated with SGD in comparison to sea surface temperature of the ocean during low-tide conditions. Consistent geographical pattern of thermal contrast was observed near the same location (lat. 22°26′54.43″N, long. 69°00′41.67″E) when multi date (11 datasets) thermal data were analysed between 2015 and 2019 in winter. Generally, low-tide conditions show more cooling of ocean surface at the SGD site compared to high-tide conditions, which indicates the process of SGD. Satellite-based assessment was further validated using field- and ship-based measurements.

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R. Ratheesh ¹, Preeti Rajput ¹, H. Bhatti ¹, A. S. Rajawat ¹, D. Ram Rajak ¹

Affiliations
1 Geo Sciences Division, GHCAG, Space Applications Centre, Indian Space Research Organisation, Ahmedabad 380 015, IN

Abstract

The coastal region of India is highly vulnerable to various threats, including coastal erosion, due to natural processes enhanced by anthropogenic influences. Shoreline change inventories are the pre-requisite for identifying the coastal stretches subjected to erosion. In this study, the shoreline of the entire Indian coast was delineated at a scale of 1 : 25,000 using IRS LISS-IV images of 2004–06 and 2014–16 time frames. The spatial shift between the shoreline of two time frames was estimated in the GIS platform and a database of shoreline changes was prepared. The eroding, accreting and stable length of the shoreline were calculated for the Indian coast along with the area of erosion and accretion. This study discusses the imperative results of shoreline mapping and the status of shoreline changes on the Indian coast. The shoreline changes in terms of erosion and accretion were assessed for 7549 km of the Indian coast. It was found that the coast is eroding along 1144 km and accretion of the coast is along 1084 km, while 5321 km of the coastline shows no changes between the two time frames. The coastal land area lost due to erosion was 3680 ha; however, the increase in land area as a result of coastal deposition was 4042 ha. The regional coastal processes and the associated shoreline changes and coastal issues related to anthropogenic impacts are also discussed in this study. The inventory of shoreline changes has been used to prepare six volumes of Shoreline Change Atlas covering the entire Indian coast. The shoreline change database forms the baseline data for planning any coastal development activity by the maritime authorities apart from the potential use by the scientific community.

Keywords

Coastal Erosion and Accretion, High Tide Line, Remote Sensing, Shoreline Changes.

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