• 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

      ABHINAV VERMA AMIT KUMAR KANHAIYA LAL

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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.

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