Effect of the Coriolis force and slowly varying flow on the Kelvin-Helmholtz instability     

D. N. Vyas  R. Singh  Krishna M. Srivastava 《Astrophysics and Space Science》1983,90(2):337-350

The effect of the Coriolis force on the Kelvin-Helmholtz instability has been investigated, in which basic velocities of fluid are varying slowly with lateral coordinatey. The problem is solved by J.W.K.B. approximation method. Parabolic and other types of profiles for wide long channel flow have also been studied in detail.  相似文献   

Comparison of ERS-SAR and spot data for sugar beet crop cover assessment     

S. P. Vyas  M. D. Steven  K. W. Jaggard 《Journal of the Indian Society of Remote Sensing》2005,33(2):315-321

The present work was aimed to compare the abilities of radar and optical satellite data to estimate crop canopy cover, which is a key component of productivity estimates. Three ERS-1 SAR images were obtained of East Anglia (UK) in 1995 and one ERS-2 SAR image in 1996. The images covered a study area around the IACR Brooms Barn Sugar Beet Research Institute. Field data comprising radiometric and biophysical measurements of the crop canopy were collected in two fields from June 22 to August 3, 1995 to coincide with ERS-1 SAR overpass dates. In 1996, field data were collected in two fields from June 11 to July 29 on a weekly basis. A previously calibrated version of the water cloud model was inverted to estimate Leaf Area Index (LAI) from ERS-1 and ERS-2 SAR backscatter and soil moisture samples. Canopy cover was estimated from the radar-estimated LAI using a standard exponential relationship that has a well-established coefficient for sugar beet. Radio-metrically and atmospherically corrected data from three SPOT images in 1995 and one SPOT image in 1996 were used to calculate the Optimised Soil Adjusted Vegetation Index (OSAVI), from which crop canopy cover was estimated using a relationship determined previously by canopy modelling. The crop cover values estimated by satellite were in good agreement with those measured on ground with the Parkinson radiometer. Radar data may be able to provide useful estimates of canopy cover for crop production modelling, especially in the case of loss of optical data due to cloud.  相似文献   

Identification of Suitable Natural Calibration Test Site for the Calibration of IRS Optical Sensors     

Shailendra S. Srivastava  Yogdeep Desai  K. S. S. Sekhar  V. R. Bhavsar  Shambhu Singh Tak  Maneesha Gupta  N. K. Vyas  K. V. S. Badarinath  B. Kartikeyan 《Journal of the Indian Society of Remote Sensing》2016,44(3):307-319

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Air photo approach to inventory of urban land use in central area case study — Kanpur     

B. Ramesh  E. A. Bueno  Anjana Vyas  J. A. Mhando 《Journal of the Indian Society of Remote Sensing》1989,17(3):115-125

The case study of Kanpur demonstrates the use of air photo approach to collect physical data, mainly landuse in central area. The study reveals that very less percentage of vacant land exists in central area for future development. Though this area consist CBD, even then commercial landuse accounts to be only 10% of total area. Selective landuse inventory analysis was carried out for the landuse categories, commercial, industrial and vacant. Reliability of aerial photo-interpretation of over all landuse map found to be 91–95% and each sub-class of landuse reliability for omission and commission error found to be within limits for planning and design purpose.  相似文献   

Effect of thermal conductivity on the gravitational instability of a magnetized rotating plasma through a porous medium in the presence of suspended particles     

R. K. Chhajlani  M. K. Vyas 《Astrophysics and Space Science》1988,145(2):223-240

The self-gravitational instability of an ionized, thermally-conducting, magnetized, rotating plasma flow through a porous medium has been studied in the presence of suspended particles. The ionized gas-particle medium has been considered rotating along and perpendicular to the vertical magnetic field. Propagation of the plasma waves has been studied for the longitudinal and the transverse modes for both the cases of rotation. A general dispersion relation has been derived with the help of relevant perturbation equations, using the method of normal mode analysis. The Jeans criterion determines the condition of gravitational instability in all the cases with some modifications introduced by the various parameters considered. Thermal conductivity replaces the adiabatic sonic speed by the isothermal one. Considering the longitudinal mode of propagation with perpendicular rotational axis, for an inviscid plasma with adiabatic behaviour the effect of both, the rotation and the suspended particles has been removed by the magnetic field. For the transverse mode of propagation with the axis of rotation parallel to the magnetic field, the viscosity removes the effect of both, the rotation and the suspended particles. Porosity reduces the effect of both, the rotation and the magnetic field, whereas the concentration of the suspended particles reduces the rotational effect.  相似文献   

Monitoring of Snow Cover Variability in Chenab Basin Using IRS AWiFS Sensor     

B. P. Rathore  S. K. Singh  Purnesh Jani  I. M. Bahuguna  Rupal Brahmbhatt  A. S. Rajawat  S. S. Randhawa  Anjana Vyas 《Journal of the Indian Society of Remote Sensing》2018,46(9):1497-1506

Monitoring of seasonal snow cover is important for many applications such as melt runoff estimation, climate change studies and strategic requirements. Contribution of seasonal snow melt runoff of Chenab River is significant and important to meet hydrological requirement at foothills. Seasonal snow cover of Chandra, Bhaga, Miyar, Bhut, Warwan and Ravi, six major tributaries of Chenab River, becomes crucial to assess the water availability. In addition, altitudinal distribution of snow cover significantly influences the melt runoff which is highly sensitive to minor variations in atmospheric temperature. In this investigation, remote sensing based Normalized Difference Snow Index technique has been used to generate 10 daily snow cover product. Snow cover monitoring of all the sub-basins were carried out for 10 years from 2004–2005 to 2013–2014 during hydrological year (October to June) using Advanced Wide Field Sensor (AWiFS) of Indian remote sensing satellite (IRS). Accumulation and ablation patterns of snow cover have also been analyzed for the six sub-basins. Accumulation and ablation pattern of snow cover, from 2004 to 2014 which shows slightly increasing trend for all the sub-basins. Meteorological data of Kelong at Bhaga sub-basin was also analysed. Average monthly snow line altitude was estimated for all the sub-basins using hypsographic curve. Chandra and Bhaga sub-basins are at higher altitude and Ravi sub-basin is at lower altitude. It was also observed that areal extent of snow reaches to lower altitude during last 5 years, particularly in Ravi sub-basin.  相似文献   

Magnetogravitational instability of an infinite homogeneous rotating plasma through a porous medium with finite electrical and thermal conductivities     

M. K. Vyas  R. K. Chhajlani 《Astrophysics and Space Science》1988,140(1):89-104

The gravitational instability of an infinite homogenous rotating plasma through a porous medium in the presence of a uniform magnetic field with finite electrical and thermal conductivities has been studied. With the help of relevant linearized perturbation equations of the problem, a general dispersion relation is obtained, which is further reduced for the special cases of rotation, parallel and perpendicular to the megnetic field acting in the vertical direction. Longitudinal and transverse modes of propagation are discussed separately. It is found that the joint effect of various parameters is simply to modify the Jeans's condition of instability. The effect of finite electrical conductivity is to remove the effect of magnetic field where as the effect of thermal conductivity is to replace the adiabatic velocity of sound by the isothermal one. Rotation has its effect only along the magnetic field in the transverse mode of propagation for an inviscid plasma, thereby stabilizing the system. Porosity reduces the effect of both, the magnetic field and the rotation, in the transverse mode of propagation in both the cases of rotation. The effect of viscosity is to remove the rotational effects parallel to the magnetic field in the transverse mode of propagation.  相似文献   

Biodegradation Studies on Acid Violet 19, a Triphenylmethane Dye,by Pseudomonas aeruginosa BCH     

Shekhar B. Jadhav  Snehal M. Yedurkar  Swapnil S. Phugare  Jyoti P. Jadhav 《洁净——土壤、空气、水》2012,40(5):551-558

Acid violet 19 (AV) belongs to the triphenylmethane (TPM) class of dyes which are potentially mutagenic or carcinogenic. However, very little studies on biodegradation of AV were reported as compared to other TPM dyes such as malachite green and crystal violet. In this study, AV was decolorized up to 98% within 30 min by Pseudomonas aeruginosa BCH. The decolorization depends on the initial dye concentration, pH, and temperature. However, the dye was decolorized under wide pH and temperature ranges with an optimum of pH 7 and 30°C. Up to 250 mg L^?1 of dye was found to be tolerated and decolorized by this strain. It showed decolorization ability for seven repeated dye addition cycles. The effect of additional carbon sources on dye decolorization was studied in which mannitol containing medium showed decolorization in 15 min. Induction in the enzyme activities of laccase, NADH‐DCIP reductase, and veratryl alcohol oxidase (VAO) indicates their involvement in AV degradation. Various analytical studies viz. UV–VIS, HPTLC, HPLC, and FTIR confirmed the biodegradation of AV by the bacterium. Based on GC‐MS analysis, a possible degradation pathway for AV was proposed. The phytotoxicity studies using Phaseolus mungo and Sorghum vulgare revealed the less toxic nature of metabolites formed after AV degradation.  相似文献   

Spatio-Temporal Coherence Based Technique for Near-Real Time Sea-Ice Identification from Scatterometer Data     

Sandip R. Oza  R. K. K. Singh  N. K. Vyas  B. S. Gohil  Abhijit Sarkar 《Journal of the Indian Society of Remote Sensing》2011,39(2):147-152

The identification of sea-ice has frequently been cited as one of the most important tasks for deriving the sea-ice parameters and to avoid erroneous retrieval of wind vector over sea-ice infested oceans using space-borne scatterometer data. Discrimination between sea-ice and ocean is ambiguous under the high wind and/or thin/scattered ice conditions. The pre-launch technique developed for Oceansat-2, utilizes the dual-polarized QuikSCAT scatterometer data by using the spatio-temporal coherence properties of sea ice in addition to backscatter coefficient and the Active Polarization Ratio. Results were compared with the operational sea-ice products from National Snow and Ice Data Center. The threshold API value of −0.025 was found optimum for sea-ice and ocean discrimination. The overall sea-ice identification accuracy achieved was of the order of 95 per cent, ranging from 92.5% (during December in Southern Hemisphere) to 98% (during March in Northern Hemisphere). The applicability of the algorithm for both the Arctic as well as Antarctic makes it suitable for its operational use with the Oceansat-2 scatterometer data.  相似文献   

Evaluation of classifiers for processing Hyperion (EO-1) data of tropical vegetation     

Dhaval Vyas  N.S.R. Krishnayya  K.R. Manjunath  S.S. Ray  Sushma Panigrahy 《International Journal of Applied Earth Observation and Geoinformation》2011

There is an urgent necessity to monitor changes in the natural surface features of earth. Compared to broadband multispectral data, hyperspectral data provides a better option with high spectral resolution. Classification of vegetation with the use of hyperspectral remote sensing generates a classical problem of high dimensional inputs. Complexity gets compounded as we move from airborne hyperspectral to Spaceborne technology. It is unclear how different classification algorithms will perform on a complex scene of tropical forests collected by spaceborne hyperspectral sensor. The present study was carried out to evaluate the performance of three different classifiers (Artificial Neural Network, Spectral Angle Mapper, Support Vector Machine) over highly diverse tropical forest vegetation utilizing hyperspectral (EO-1) data. Appropriate band selection was done by Stepwise Discriminant Analysis. The Stepwise Discriminant Analysis resulted in identifying 22 best bands to discriminate the eight identified tropical vegetation classes. Maximum numbers of bands came from SWIR region. ANN classifier gave highest OAA values of 81% with the help of 22 selected bands from SDA. The image classified with the help SVM showed OAA of 71%, whereas the SAM showed the lowest OAA of 66%. All the three classifiers were also tested to check their efficiency in classifying spectra coming from 165 processed bands. SVM showed highest OAA of 80%. Classified subset images coming from ANN (from 22 bands) and SVM (from 165 bands) are quite similar in showing the distribution of eight vegetation classes. Both the images appeared close to the actual distribution of vegetation seen in the study area. OAA levels obtained in this study by ANN and SVM classifiers identify the suitability of these classifiers for tropical vegetation discrimination.  相似文献