Browsing by Author "Om Pal"

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Active-Passive Approach for NISAR High Resolution Soil Moisture Products: Retrieval and Accuracy Assessment over Indian Cropland
(Institute of Electrical and Electronics Engineers Inc., 2021) Dharmendra Kumar Pandey; Srinivasa Teja Noothi; M. Shashi; Prashant K. Srivastava; Anup Das; Om Pal; Kapil Rohilla; Ravindra Prawasi; Nijbul H. Sekh; Sushma Bisht; Deepak Putrevu; Arundhati Misra; Raj Kumar
Soil moisture is an essential variable in agricultural applications for irrigation scheduling, crop water requirements and pest management etc. However, currently available global satellite microwave radiometer derived soil moisture products are inadequate due to coarse spatial resolution for such applications. In order to improve spatial resolution, SMAP (Soil Moisture Active Passive) mission has first time demonstrated the potential of combining microwave radiometer and radar data based on Active-Passive approach to produce 3-9 km soil moisture globally. However, this approach has not been well tested quantitatively at sub km (<1km) grid resolution using spaceborne observations. In this work, we adopted and tested active-passive approach to integrate radiometer derived coarse resolution soil moisture (SMAP L-band radiometer) with fine resolution radar backscatter (Sentinel-1 C-band SAR) to downscale soil moisture at multiple grid resolution (100 m, 500m and 1000 m). The impact of scale on the robustness of the algorithm is analyzed by assessing the soil moisture retrieval accuracy. Detailed validation was attempted using Multi-Scale Field Sampling Framework (MFSF) over selected agricultural cropland study site. The results obtained are very encouraging, showing the potential of Active-Passive approach for high spatial soil moisture with correlation of 0.75, 0.76 & 0.68 and ubRMSE of 4.94%, 6.07% & 7.21% for 100m, 500m and 1km respectively. Based on the above assessment as pre-cursor study, Active-Passive approach will be the potential candidate for utilizing NISAR data to deliver high spatial resolution soil moisture operational products along with radiometer. © 2021 IEEE.
Long term and electrochemical corrosion investigation of cold worked AISI 316L and 316LVM stainless steels in simulated body fluid
(Royal Society of Chemistry, 2014) Mohd Talha; C.K. Behera; Sudershan Kumar; Om Pal; Gurmeet Singh; O.P. Sinha
AISI 316L and 316LVM stainless steels in annealed (solution quenched from 1050°C) and rolled (10% and 20% cold work) conditions were assessed for their long term and electrochemical corrosion behavior in simulated body fluid (SBF) at 37°C. The techniques used for the characterization of their corrosion resistance were the weight loss method, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. Scanning electron microscopy (SEM) was used to investigate the surface morphologies of the alloys after the polarization tests. Surface analysis of the films formed on the steels in SBF was carried out using X-ray photoelectron spectroscopy (XPS). The weight loss and corrosion rate decreased with increasing degree of cold working. The resistance of a passive film is directly related to the material's corrosion resistance and increases on cold working, indicating the formation of a larger protective oxide layer on the surface of cold worked samples. The corrosion current density (Icorr) decreased with increasing degree of cold working and, simultaneously, the corrosion potentials (Ecorr) became more positive. On observing the pit morphologies using SEM, shallower and smaller pits were associated with cold worked samples as compared to annealed samples. The XPS results indicated that the main elements in the passive oxide layer were Cr, Fe and Mo. The Cr-oxide (ox):Cr-hydroxide (hy) ratio and the Fe-oxide (ox):Fe-hydroxide (hy) ratio were observed to be higher for rolled materials than for annealed materials, indicating that the passive films on rolled materials are more protective and improve the corrosion resistance. This journal is © the Partner Organisations 2014.