Modified Dubois Model for Estimating Soil Moisture with Dual Polarized SAR Data     

S. Srinivasa Rao  S. Dinesh kumar  S. N. Das  M. S. S. Nagaraju  M. V. Venugopal  Prashant Rajankar  Pankaj Laghate  M. Sivaprasad Reddy  A. K. Joshi  J. R. Sharma 《Journal of the Indian Society of Remote Sensing》2013,41(4):865-872

This paper discusses a new methodology to estimate soil moisture in agriculture region using SAR data with the use of HH and HV polarization. In this study the semi empirical model derived by Dubois et al. (IEEE Transactions on Geoscience and Remote Sensing, 33(4), 915–926, 1995) was modified to work using σ _HH instead of two like polarization equations σ_HH, σ_VV so that soil moisture can be obtained for the larger area frequently. The field derived roughness correlated with the cross polarization ratio (HV/HH) to replace the one unknown parameter ‘s’ in the Dubois model and hence the dielectric constant was derived by inverting the Dubois model equation (HH). The Topp et al. (Water Resources Research, 16(3), 574–582, 1980) model was used to retrieve soil moisture using the dielectric constant. The mid incidence angle was used to overcome the incident angle effect and it worked successfully to the larger extent. The result is realistic overall, especially where surface has less variation in the roughness and vegetation since the penetration capability of C-band is limited when plant grows hence model valid in the initial period of cultivation. The derived model is having good scope for soil moisture monitoring with the present availability of Indian RISAT data.  相似文献   

The influence of negatively charged heavy ions on the kinetic Alfven wave in a cometary environment     

Venugopal Chandu  E. Savithri Devi  R. Jayapal  George Samuel  S. Antony  G. Renuka 《Astrophysics and Space Science》2012,339(1):157-164

Kinetic Alfven waves are important in a wide variety of areas like astrophysical, space and laboratory plasmas. In cometary environments, waves in the hydromagnetic range of frequencies are excited predominantly by heavy ions. We, therefore, study the stability of the kinetic Alfven wave in a plasma of hydrogen ions, positively and negatively charged oxygen ions and electrons. Each species was modeled by drifting ring distributions in the direction parallel to the magnetic field; in the perpendicular direction the distribution was simulated with a loss cone type distribution obtained through the subtraction of two Maxwellian distributions with different temperatures. We find that for frequencies w^* < w_{cH ⁺}\omega^{*} < \omega_{c\mathrm{H}^{ +}} (ω ^∗ and w_{cH ⁺}\omega_{c\mathrm{H}^{ +}} being respectively the Doppler shifted and hydrogen ion gyro-frequencies), the growth rate increases with increasing negatively charged oxygen ion densities while decreasing with increasing propagation angles, negative ion temperatures and negative ion mass.  相似文献   

Apposite of atmospheric electric parameters with the energy coupling function (ε) during geomagnetic storms at high latitude     

C.P. Anil Kumar  C. Panneerselvam  K.U. Nair  H. Johnson Jeyakumar  C. Selvaraj  S. Gurubaran  C. Venugopal 《Atmospheric Research》2009,91(2-4):201-205

In this paper we are concerned with the variation of the atmospheric electric field and the air–earth current due to the excessive power generated by the solar wind-magnetosphere dynamo during geomagnetic storms, recorded at Maitri in Antarctica during 2004. A major part of the power generated by the solar wind-magnetosphere dynamo is used in the formation of the ring current and the rest is utilized for Joule heating and auroral particle precipitation. The method adopted by Frank-Kamenetsky et al. [Frank-Kamenetsky A.V., Troshichev O.A., Burns G.B., Papitashvili V.O., 2001. Variations of atmospheric electric field in the near-pole region related to the interplanetary magnetic field. J. Geophys. Res. 106, A1, 179–190.] was utilized to delineate the variations due to the signatures of tropical thunderstorm activity from the geoelectric data; while statistical methods used in our earlier studies were used to delimit variation due to the constant buffeting of the solar wind. We find that the solar wind-magnetosphere energy coupling function (ε) to be well correlated with the atmospheric electric parameters during the onset of geomagnetic disturbances. However the correlation breaks down during minor storms and sub-storm events.  相似文献   

Differential thermal analysis and thermogravimetric studies of the Kaladgi (precambrian) argillites,Karnataka     

M J Chandrasekhara Gowda  J S Venugopal  B V Govindarajulu 《Journal of Earth System Science》1978,87(7):101-107

The Kaladgi argillites show heterogeneity in textural and physical properties. Differential thermal analysis and thermogravimetric studies have revealed that the argillites contain illite with montmorillonite, quartz and biotite. The calc-rich shale contains illite and kaolinite with total absence of montmorillonite. The mineralogical significance of the depositional environment of the Kaladgi (precambrian) sea has been discussed.  相似文献   

Interrelationship between cloud cover and sensible heat flux over land during MONTBLEX-1990     

T. Venugopal  P. Seetaramayya  A. R. Dhakate 《Journal of Earth System Science》2005,114(4):421-426

Micro-meteorological tower observations of MONTBLEX (Monsoon Trough Boundary Layer Experiment)-1990, combined with routine surface observations at Jodhpur in the dry convective sector of Indian summer monsoon trough are used to examine the interrelationship between total cloud cover (TCC) and surface sensible heat flux (SHF) during the summer monsoon of 1990. A significant inverse relationship between TCC and SHF is found during various Intensive Observation Periods of the experiment. This relationship holds for the various methods of estimation of SHF.  相似文献   

An experimental investigation of hydrodynamic coefficients for a vertical truncated rectangular cylinder due to regular and random waves     

V. Vengatesan  K. S. Varyani  N. Barltrop   《Ocean Engineering》2000,27(3)

The research into hydrodynamic loading on ocean structures has concentrated mostly on circular cross-section members and relatively limited work has been carried out on wave loading on other cross-sections such as rectangular sections. These find applications in many offshore structures as columns and pontoons in semi-submersibles and tension-leg platforms. The present investigation demonstrates the behaviour of rectangular cylinders subject to wave loading and also supplies the hydrodynamic coefficients for the design of these sections.This paper presents the results of wave forces acting on a surface piercing truncated rectangular cylinder set vertically in a towing tank. The experiments are carried out in a water depth of 2.2 m with regular and random waves for low Keulegan–Carpenter number up to 6. The rectangular cylinder is of 2 m length, 0.2 m breadth and 0.4 m width with a submergence depth of 1.45 m from still water level. Based on Morison equation, the relationship between inertia and drag coefficients are evaluated and are presented as a function of KC number for various values of frequency parameter β, for two aspect ratios of cylinders, equals to 1/2 and 2/1. Drag and inertia coefficients obtained through regular wave tests are used for the random wave analysis to compute the in-line force spectrum.The results of the experiments show the drag and inertia coefficients are strongly affected by the variation in the aspect ratios of the cylinder. The drag coefficients decreases and inertia coefficients increases with increase in Keulegan–Carpenter number up to the range of KC number tested. The random wave results show a good correlation between measured and computed force spectrums. The transverse forces in both regular and random waves are found to be small compared to in-line forces.  相似文献   

Spectral ultraviolet radiation instrument and preliminary measurements in Mountainous terrain     

Inge Dirmhirn  C. R. Sreedharan  G. Venugopal 《Theoretical and Applied Climatology》1993,46(4):219-228

Summary Measurements of spectral ultraviolet irradiance require spectroradiometers with high resolution and stability, and well known behavior of the instrument. A UV-spectrophotometer is described and methods of calibrations are shown. A set of measurements in the Utah Rocky Mountains (Snowbird-Hidden Peak, in 3300 m elevation) compared to those at the Wasatch Front (Logan, 1400 m) is discussed. Several sets of measurements are used to show the effect of solar zenith angle, elevation and cloudcover on direct solar and diffuse irradiance.At the time of the instrument design and measurements all were at Utah State University, Department of Soil Science and Biometeorology, Logan, Utah.With 11 Figures  相似文献   

The effect of wave period filtering on wave power extraction and device tuning     

Vengatesan Venugopal  George H. Smith 《Ocean Engineering》2007,34(8-9):1120-1137

The variations in the quantity of wave power available to a wave energy converter by filtering out short-period waves have been examined in this paper. Ocean wave data recorded at three different locations and water depths around northern Europe are used for this purpose along with numerically synthesized wave time series. A wave power ratio, defined as the ratio between the wave power for the filtered and unfiltered data, is calculated for each data set, and the variation of this quantity with the degree of filtering is investigated. Two new parameters namely, R and S are defined to quantify the effect of this filtering on the variation of wave-to-wave period and height. It is shown that removing the shorter period waves has little effect upon the power available for extraction but may significantly reduce the rate at which the wave energy converter must retune to achieve optimum power conversion.  相似文献   

Proceedings of the Workshop on Mineral Sector of India – Post MMDR Amendment Act, 2015     

T. N. Venugopal  Subhajyoti Das 《Journal of the Geological Society of India》2018,91(4):512-512

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Evidence for inherent nonlinearity in temporal rainfall     

Stéphane G. Roux  V. Venugopal  Kurt Fienberg  Alain Arneodo  Efi Foufoula-Georgiou 《Advances in water resources》2009

We examine the underlying structure of high resolution temporal rainfall by comparing the observed series with surrogate series generated by a invertible nonlinear transformation of a linear process. We document that the scaling properties and long range magnitude correlations of high resolution temporal rainfall series are inconsistent with an inherently linear model, but are consistent with the nonlinear structure of a multiplicative cascade model. This is in contrast to current studies that have reported for spatial rainfall a lack of evidence for a nonlinear underlying structure. The proposed analysis methodologies, which consider two-point correlation statistics and also do not rely on higher order statistical moments, are shown to provide increased discriminatory power as compared to standard moment-based analysis.  相似文献