Browsing by Author "B. Verma"

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Development of a new vegetation modulated soil moisture index for the spatial disaggregation of SMAP soil moisture data product
(Elsevier Ltd, 2024) J. Sharma; R. Prasad; P.K. Srivastava; S.A. Yadav; S.K. Singh; B. Verma
Microwave remote sensing serves as a complementary tool for soil moisture mapping and monitoring in comparison to the optical and the infrared remote sensing. The key advantage of microwave remote sensing lies in its ability to estimate soil moisture irrespective of weather or atmospheric conditions. However, existing microwave passive soil moisture products are currently available only at a coarse spatial resolution, limiting their utility for various regional hydrological applications. Various studies have introduced different approaches to downscale these satellite soil moisture data products but the modulation of vegetation present on the soil surface is still a challenging task in the field of downscaling satellite soil moisture data products. Therefore, this study presents a novel vegetation modulated soil moisture index developed by incorporating the MODIS (MODerate resolution Imaging Spectroradiometer) NDVI (Normalized Difference Vegetation Index), and LST (Land Surface Temperature). This newly derived index is then used to downscale the coarse resolution SMAP (Soil Moisture Active Passive) soil moisture data product. The proposed downscaling method has been validated using ground - measured soil moisture and compared with conventional downscaling approaches. It is found that the newly developed method, which has a bias error of −0.004 m3/m3 an Unbiased Root Mean Square Error (ubRMSE) of 0.068 m3/m3 of the downscaled soil moisture and demonstrates more intricate spatial variations. © 2024 Elsevier Ltd
Experimental study on thermal performance of pulsating heat pipe with al2o3-deionizedwater nanofluid at different orientations
(2013) B. Verma; V.L. Yadav; K.K. Srivastava
Thermal resistance as a function of heat load and start-up temperature with respect to time have been investigated for a pulsating heat pipe (PHP) at different inclination angles. PHP was made of 1.45 mm inner diameter copper tubes having 6 turns. Al2O3 nanofluid (concentration 0.25%, 0.5, 1.0, 1.25, 1.5, and 2.5% by wt.) with particle size 45 nm at an optimum filling ratio of 50% was used. It is found that as the concentration increases from 0.25% to 1.0% there is considerable decrease in thermal resistance as compared to that of the base fluid but as the concentration increases from 1.25% to 2.5% the thermal performance deteriorates. Optimum concentration of nanoparticles was 1.0% by wt. in base fluid with respect to start-up and thermal resistance for PHP in vertical orientation and 45. inclination, while in horizontal orientation 0.5% by wt. concentration showed the best results. Maximum decrease in thermal resistance with respect to deionized (DI) water was observed at 50Wfor 1.0% nanofluid concentration by wt. at 45. inclination, which was 33.6%. Heat transfer coefficients at evaporator and condenser are also investigated at vertical mode of operation. © 2013 by Begell House, Inc.