Imaging Spectropolarimeter for the Multi-Application Solar Telescope at Udaipur Solar Observatory: Characterization of Polarimeter and Preliminary Observations     

Alok Ranjan Tiwary  Shibu K. Mathew  A. Raja Bayanna  P. Venkatakrishnan  Rahul Yadav 《Solar physics》2017,292(4):49

The Multi-Application Solar Telescope (MAST) is a 50 cm off-axis Gregorian telescope that has recently become operational at the Udaipur Solar Observatory (USO). An imaging spectropolarimeter is being developed as one of the back-end instruments of MAST to gain a better understanding of the evolution and dynamics of solar magnetic and velocity fields. This system consists of a narrow-band filter and a polarimeter. The polarimeter includes a linear polarizer and two sets of liquid crystal variable retarders (LCVRs). The instrument is intended for simultaneous observations in the spectral lines 6173 Å and 8542 Å, which are formed in the photosphere and chromosphere, respectively. In this article, we present results from the characterization of the LCVRs for the spectral lines of interest and the response matrix of the polarimeter. We also present preliminary observations of an active region obtained using the spectropolarimeter. For verification purposes, we compare the Stokes observations of the active region obtained from the Helioseismic Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) with that of MAST observations in the spectral line 6173 Å. We find good agreement between the two observations, considering the fact that MAST observations are limited by seeing.  相似文献   

Comparison of Vegetation Indices from Two Ground Based Sensors     

S. Pradhan  V. K. Sehgal  K. K. Bandyopadhyay  R. N. Sahoo  P. Panigrahi  C. M. Parihar  S. L. Jat 《Journal of the Indian Society of Remote Sensing》2018,46(2):321-326

The best and commonly used ground-based sensor to monitor crop growth, ASD FieldSpecPro Spectroradiometer (Analytical Spectral Devices, Boulder, CO, USA) is a passive sensor, which can be used under adequate light condition. However, now-a-days active sensors such as GreenSeeker? (GS) handheld crop response (Trimble Agriculture division, USA) are used for monitoring crop growth and are flexible in terms of timeliness and illumination conditions besides being cheaper than the ASD. Before its wide use, the suitability and accuracy of GS should be assessed by comparing the NDVI measured by this instrument with that by ASD, under diverse wheat growing conditions of India. Keeping this in view, the present experiment was undertaken with the following objectives: (1) to find out the temporal variation of NDVI measured both by ASD and GS treatments, (2) to find out relationship between the NDVI measured through ASD and GS and, (3) to evaluate the suitability of GS for NDVI measurements. It was observed that the numerical value of NDVI as measured by GS was always significantly (P < 0.05) lower than that measured by ASD for all the experiments under study. The NDVI-ASD and NDVI-GS were significantly positively correlated (P < 0.01) with the correlation coefficients being +0.94, +0.88 and +0.87 for irrigation and nitrogen experiment, irrigation and cultivars experiment, and tillage, residue and nitrogen experiments, respectively. Further, the regression equation developed between the NDVI-ASD and NDVI-GS: [NDVI-GS = 1.070 × (NDVI-ASD ? 0.292] can be successfully used to compute the NDVI of ASD from that computed by GS.  相似文献   

Exact solutions in (2+1)-dimensional anti-de Sitter space-time admitting a linear or non-linear equation of state     

Ayan Banerjee  Farook Rahaman  Kanti Jotania  Ranjan Sharma  Mosiur Rahaman 《Astrophysics and Space Science》2015,355(2):353-359

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Non-existence of five dimensional string cosmological models in Riemannian and Lyra geometries     

G. Mohanty  R. R. Sahoo  B. K. Bishi 《Astrophysics and Space Science》2009,319(1):75-79

In this paper, we have attempted to construct five dimensional string cosmological models in Riemannian and Lyra geometries. It is found that cosmic string models do not survive in both the theories. Subsequently, the vacuum cosmological models are constructed and discussed.  相似文献   

GIS-based vulnerability mapping of the coastal stretch from Puri to Konark in Odisha using analytical hierarchy process     

Behera  Rashmisikha  Kar  Abhipsa  Das  Manas Ranjan  Panda  Prachi Prava 《Natural Hazards》2019,96(2):731-751

Natural Hazards - The 485-km-long coastline of Odisha, a state in the northeastern part of the Indian peninsula, is potentially vulnerable to several disaster events that take place frequently. In...  相似文献   

A geomorphology‐based integrated stream–aquifer interaction model for semi‐gauged catchments     

Soumyaranjan Sahoo  Bhabagrahi Sahoo 《水文研究》2019,33(9):1362-1377

Many of the existing stream–aquifer interaction models available in the literature are very complex with limited applicability in semi‐gauged and ungauged catchments. In this study, to estimate the influent and effluent subsurface water fluxes under limited geo‐hydrometeorological data availability conditions, a simple stream–aquifer interaction model, namely, the variable parameter McCarthy–Muskingum (VPMM) hillslope‐storage Boussinesq (hsB) model, has been developed. This novel model couples the VPMM streamflow transport with the hsB groundwater flow transport modules in online mode. In this integrated model, the surface water–groundwater flux exchange process is modelled by the Darcian approach with the variable hydraulic heads between the river stage and groundwater table accounting for the rainfall forcing. Considering the exchange fluxes in the hyporheic zone and lateral overland flow contribution, this approach is field tested in a typical 48‐km stretch of the Brahmani River in eastern India to simulate the streamflow and its depth with the minimum Nash–Sutcliffe efficiency of 94% and 88%; the maximum root mean square error of 134 m³/s and 0.35 m; and the minimum index of agreement of 98% and 97%, respectively. This modelling approach could be very well utilized in data‐scarce world‐river basins to estimate the stream–aquifer exchange flux due to rainfall forcings.  相似文献   

Comparative analysis of contributing parameters for rainfall-triggered landslides in the Lesser Himalaya of Nepal   总被引：6，自引：0，他引：6  

Ranjan Kumar Dahal  Shuichi Hasegawa  Minoru Yamanaka  Santosh Dhakal  Netra Prakash Bhandary  Ryuichi Yatabe 《Environmental Geology》2009,58(3):567-586

In the Himalaya, people live in widely spread settlements and suffer more from landslides than from any other type of natural disaster. The intense summer monsoons are the main factor in triggering landslides. However, the relations between landslides and slope hydrology have not been a focal topic in Himalayan landslide research. This paper deals with the contributing parameters for the rainfall-triggered landslides which occurred during an extreme monsoon rainfall event on 23 July 2002, in the south-western hills of Kathmandu valley, in the Lesser Himalaya, Nepal. Parameters such as bedrock geology, geomorphology, geotechnical properties of soil, and clay mineralogy are described in this paper. Landslide modeling was performed in SEEP/W and SLOPE/W to understand the relationship of pore water pressure variations in soil layers and to determine the spatial variation of landslide occurrence. Soil characteristics, low angle of internal friction of fines in soil, medium range of soil permeability, presence of clay minerals in soil, bedrock hydrogeology, and human intervention were found to be the main contributing parameters for slope failures in the region.  相似文献   

Central Himalayan crystallines as the primary source for the sandstone–mudstone suites of the Siwalik Group: New geochemical evidence     

Nikesh Ranjan  D.M. Banerjee   《Gondwana Research》2009,16(3-4):687-696

Geochemistry of the Sub-Himalayan foreland basin Siwalik sediments has been used for interpreting the nature of the source rocks. This study has shown that the compositional changes are a function of stratigraphic height, demonstrated by the upward increase of P₂O₅, Na₂O, CaO, MgO and SiO₂ content from Lower to the Upper Siwalik rocks. On the other hand, K₂O, Fe₂O₃, TiO₂ and Al₂O₃ show decrease with the increasing stratigraphic height. These trends are a clear reflection of time-controlled changes in the source lithology. Ratios such as Eu/Eu*, (La/Lu)_cn, La/Sc, Th/Sc, La/Co, and Cr/Th suggest a prominent felsic source area for the Siwalik sediments. Chondrite-normalized REE pattern with LREE enrichment and moderately flat HREE pattern with sharp negative Eu anomaly are attributed to a felsic source. Contrary to the existing belief, this study has ruled out any contribution from the mafic sources and highlighted the compositional similarities of Siwalik sediments with the crustal proxies like PAAS, NASC and UCC. The geochemical data point to a significant role played by the Precambrian and early Paleozoic granitic rocks of the Himalayan tectogene in shaping the composition of the foreland sediments. The variable CIA values and marked depletion in Na, Mg and Ca exhibited by the Lower, Middle and Upper Siwalik sediments reflect variable climatic zones and variations in the rate of tectonic uplift of the source area. Our results demonstrate that in the Lower Siwalik and part of the Middle Siwalik, Higher Himalayan Crystalline sequence (HHCS) was the primary source area with minor contributions by the meta-sedimentary succession of the Lesser Himalaya. Later, during the deposition of the upper part of the Middle Siwalik and Upper Siwalik, the source terrain switched positions. These two prominent source terrains supplied sediments in steadily changing proportion through time.  相似文献   

Love waves in the fiber-reinforced layer over a gravitating porous half-space   总被引：2，自引：2，他引：0  

Ranjan Chattaraj  Sapan K. Samal 《Acta Geophysica》2013,61(5):1170-1183

This paper aims to study the propagation of Love waves in fiber-reinforced layer lying over a gravitating anisotropic porous half-space. The closed form of dispersion equation has been derived for the Love waves in terms of Whittaker function and its derivative, which are further expanded asymptotically, retaining the terms up to second degree. The frequency equation shows that the transverse and longitudinal rigidity of reinforced material, as well as gravity and porosity of the porous halfspace have significant effect on the propagation of Love waves. The study reveals that the increment in width of reinforced layer decreases the phase velocity. For a particular width of the reinforced layer, it is also observed that the phase velocity increases with increasing porosity of the half-space, but it decreases with increasing gravity.  相似文献   

PCA–based composite drought index for drought assessment in Marathwada region of Maharashtra state,India     

Prajapati  V. K.  Khanna  M.  Singh  M.  Kaur  R.  Sahoo  R. N.  Singh  D. K. 《Theoretical and Applied Climatology》2022,149(1-2):207-220

Theoretical and Applied Climatology - This paper presents a composite approach for drought characterization and monitoring using in situ and remote sensing-based drought indicators. The study was...  相似文献