• Amit Kumar

      Articles written in Journal of Earth System Science

    • Climatic control on extreme sediment transfer from Dokriani Glacier during monsoon, Garhwal Himalaya (India)

      Amit Kumar Akshaya Verma Dwarika Prasad Dobhal Manish Mehta Kapil Kesarwani

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      In the Himalayas, most of the glaciers are covered by thick debris, especially in the ablation zone. Supraglacial debris cover might play an important role for sediment budget of the glaciated area or for the ablation of ice masses mantled in debris. During summer season, proglacial meltwater carries considerable amount of suspended sediment. The deglaciated area provides a ready source of sediment during Indian Summer Monsoon (ISM). The heavy sediment load from the glaciers affects the hydropower generation, irrigation and drinking water supply. Therefore, to understand the sediment delivery from glaciated basins, characteristics and variation of the suspended sediment concentrations in the proglacial meltwater stream, Dokriani Glacier, have been monitored during the ablation season (May– September). Suspended sediment samples were collected near the snout of Dokriani Glacier, Garhwal Himalaya, in 2010 and 2011. Results show that mean monthly suspended sediment concentrations (SSC) were 1499, 2303, 3845 and 1649 mg/l for the months June, July, August, and September, respectively, indicating highest concentration in August followed by July. Over the period of recording, daily mean suspended concentration in the melt stream varied from 13–9798.2 mg/l, which is very high, caused due to a flash flood event during the monitoring period. The mean daily suspended sediment concentration was computed to be 2196 mg/l. The suspended sediment concentration begins to increase with discharge from May and reduces in September. Present study provides TRMM (Tropical Rainfall Measuring Mission) derived and field based hydro-meteorological insight about severe rainstorms during the years 2010 and 2011 in the study area, which transported large amounts of sediment.

    • Kharif crop characterization using combination of SAR and MSI Optical Sentinel Satellite datasets


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      In the present study, the differences in the kharif crop reflectance at varied wavelength regions and temporal SAR backscatter (at VV and VH polarizations) during different crop stages were analyzed to classify crop types in parts of Ranchi district, East India using random forest classifier. The spectral signature of crops was generated during various growth stages using temporal Sentinel-2MSI (optical) satellite images. The temporal backscatter profile that depends on the geometric and di-electric properties of crops were studied using Sentinel-1 SAR data. The spectral profile exhibited distinctive reflectance at the NIR (0.842 $\mu$m) and SWIR (1.610 $\mu$m) wavelength regions for paddy (Oryza sativa; $\sim 0.25$ at NIR, $\sim 0.27$ at SWIR), maize (Zea mays; $\sim 0.24$ at NIR, $\sim 0.29$ at SWIR) and finger millet (Eleusine coracana, $\sim 0.26$NIR, $\sim 0.31$ at SWIR) during pre-sowing season (mid-June). Similar variations in crop’s reflectance at their different growth stages (vegetative to harvesting) were observed at various wavelength ranges. Further, the variations in the backscatter coefficient of different crops were observed at various growth stages depending upon the differences in sowing–harvesting periods, field conditions, geometry, and water presence in the crop field, etc. The Sentinel-1 SAR based study indicated difference in the backscatter of crops (i.e., $\sim -18.5$ dB (VH) and $\sim -10$ dB (VV) for paddy, $\sim -14$ dB (VH) and $\sim -7.5$ dB(VV) for maize, $\sim -14.5$ dB and $\sim -8$ dB (VV) for finger millet) during late-July (transplantation for paddy; early vegetative for maize and finger millet). These variations in the reflectance and backscatter values during various stages were used to deduce the best combination of the optical and SAR layers in order to classify each crop precisely. The GLCM texture analysis was performed on SAR for better classification of crop fields with higher accuracies.The SAR-MSI based kharif crop assessment (2017) indicated that the total cropped area under paddy, maize and finger millet was 24,544.55, 1468.28 and 632.48 ha, respectively. The result was validated with ground observations, which indicated an overall accuracy of 83.87% and kappa coefficient of 0.78. The high temporal, spatial spectral agility of Sentinel satellite are highly suitable for kharif crop monitoring. The study signifies the role of combined SAR–MSI technology for accurate mapping and monitoring of kharif crops.

    • Geoecological integrity index for assessment and prioritisation of watersheds in the Indian northwestern Himalayan region using geoinformatics


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      Biotic, abiotic and anthropogenic factors are considered in isolation for prioritisation of watersheds. Instead, it requires a multidisciplinary geoecolocical approach. The geoecology based prioritisation provides opportunities to assess the region by evaluating these multiple factors in combination. Thus, Geoecological Integrity Index (GII) was developed for prioritisation of Baner River watersheds of Indian northwestern Himalayan region by integrating biotic, abiotic and anthropogenic factors as the region is facing geological and ecological instability. Forest cover density and net primary productivity were used as biotic factors and drainage morphometry, soil erosion, and patches were used as abiotic factors. Population density of the watershed was considered as an anthropogenic factor. Weighed overlay analysis was carried out to understand the influence of each of these factors on watershed prioritisation. These factors were integrated to arrive at cumulative weights (GII) for micro-watersheds. With the help of GII, out of 110 micro-watersheds, 11 were prioritised as very high actionable, 32 as high actionable, 52 as moderately actionable and 15 as of minimal action, requiring suitable actions in a prioritised manner to conserve and manage. The study presents an approach for geoecological assessment of watersheds that can be replicated in watersheds of other Himalayan regions or areas having similar geoecological conditions.


      $\bullet$ Geoecological Integrity Index (GII) was developed for prioritisation of watersheds in Indian north-western Himalaya.

      $\bullet$ GII was developed considering biotic, abiotic and anthropogenic factors, which are generally treated in isolation.

      $\bullet$ Geoecological factors were integrated to arrive at cumulative weights (GII) for micro-watersheds.

      $\bullet$ Out of 110 micro-watersheds, 11 were prioritised as very high actionable, 32 as high actionable, 52 as moderately actionable and 15 as of minimal action, requiring suitable actions for its conservation and management.

      $\bullet$ Study provided an approach for geoecological assessment of watersheds that can be replicated in any other watersheds having similar conditions.

    • Dimensionality and directionality analysis of magnetotelluric data by using different techniques: A case study from northern part of Saurashtra region, India


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      Magnetotelluric (MT) data has been collected along 32 stations along E–W profile in northern part and eight LMT (long period MT) stations in north-central part of Saurashtra region. Dimensionality analysis is carried out prior to MT modelling for obtaining the subsurface dimension as well as the direction of the underlying substructures. To estimate the subsurface dimensionality from MT data, different techniques Swift skew, Bhar’s skew, normalized weights, phase tensor (PT) analysis and Wall’s rotational invariant approach have been applied. These results suggest 1D structure for lower periods (0.01–1 s) and 3D structure for higher periods (1–10000 s) along two different profiles indicating that the study area is highly heterogeneous. Regional strike has been estimated through phase tensor (PT) and Groom–Bailey (GB) techniques suggests N40$^{\circ}$ E regional strike direction that correlates well with the Delhi–Aravalli tectonic trend. 2D modelling of MT/LMT data sets brings out different resistivity and conductivity blocks. Basaltic magmatic intrusion and its recrystallization have resulted in resistivity blocks with conductivity anomalies (trapped fluids) in between them. It has been reflected as 3D structures at higher periods. Different sedimentary basins at shallow depth are observed as 1D structure in dimensionality analysis.


      $\bullet$ Magnetotelluric (MT)/long period Magnetotelluric (LMT) survey is carried out in northern part of Saurashtra. Different dimensionality techniques were used to assess the structural dimensionality of the electrical conductivity of the earth and were compared.

      $\bullet$ Analysis of MT sites by using various methods indicates the electrical conductivity structure is less complex at the shallowest depths with mixed 1D and 2D cases that are affected by galvanic distortion. Both MT/LMT denote complex 3D nature from middle and lower depths.2D inversion of MT/LMT data brings out large-scale heterogeneities in the crust. This is attributed to different resistive and conductive blocks present at mid-crustal depths and extending up to lower crustal depths and correlates with dimensionality analysis.

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