Raj Kumar
Articles written in Journal of Earth System Science
Volume 94 Issue 3 November 1985 pp 249-259
A study on the sensitivity of the radar scattering coefficient to oceanic winds
Sensitivity of the radar scattering coefficient to the oceanic wind vector in the midangular range for frequencies from L- to Ku- band is studied. This is based on computations of scattering coefficient via the two-scale scattering theory employing a semi-empirical model for the ocean spectrum suggested by Fung and Lee and the slope distribution by Cox and Munk. Higher frequency and incident angles of over 45 degrees seem to yield better wind sensitivity.
Volume 95 Issue 1 March 1986 pp 75-82
Quasi-specular sea scatter with modified reflection coefficient
The paper deals with the relationship between the sea surface wind speed (
Volume 96 Issue 3 December 1987 pp 259-266
Selection of optimum frequency of a wind scatterometer
Abhijit Sarkar Raj Kumar Mannil Mohan
The problem of selecting the optimum operating frequency of a scatterometer, used for remote sensing of sea surface wind speed has been addressed by applying the criteria of maximum sensitivity of backscattering coefficient to wind speed as well as its correlation with wind speed. The backscattering coefficient values for sea surface were computed by the two-scale scattering theory. To compute the atmospheric transmittance, 753 clear sky atmospheres over Indian Ocean were used. While the correlation coefficient was uniform (0.94) throughout the frequency range of 1 to 30GHz, only frequencies above 5GHz were found sensitive enough to yield a wind speed accuracy of ±2msec−1 and better, the accuracy improving with frequency.
Volume 97 Issue 2 December 1988 pp 192-192 Erratum
Volume 100 Issue 4 December 1991 pp 379-388
Static deformation of two welded half-spaces due to very long strike-slip dislocations
Raj Kumar Sharma Nat Ram Garg Kuldip Singh
Closed form analytic expressions for displacement and stresses at any point of either of the two homogeneous, isotropic, perfectly elastic half-spaces in welded contact due to very long strike-slip dislocations are obtained. Both cases of vertical and horizontal strike-slip dislocations are discussed in detail. Variation of the displacement with horizontal distance from the fault and with vertical distance from the interface for a vertical strike-slip fault is studied numerically.
Volume 101 Issue 3 September 1992 pp 255-268
The closed-form analytic expressions for the displacement and stresses at any point of an elastic layer lying over a base due to a very long vertical strike-slip dislocation are obtained. The interface between the layer and the base is assumed to be either ‘smooth-rigid’ or ‘rough-rigid’ or ‘welded’. The variations of displacement and stresses with the horizontal distance from the fault for different types of coupling of the layer with the base have been studied. It is found that the displacement for ‘welded interface’ lies between the displacements due to ‘smooth rigid’ and ‘rough-rigid’ interfaces for different positions of the observer and different values of the ratio of rigidities of the layer and half-space.
Volume 107 Issue 3 September 1998 pp 213-216
An analytical source function for a coupled hybrid wave model
M Mohan Abhijit Sarkar Raj Kumar
An analytical form for the source function is formulated by comparing the fetch-limited approximation of the Ocean Wave Transport equation and the empirical equation for the fetch-dependent wave forecast nomograms. The source function thus generated has been utilised in the numerical model based on Toba’s formulation of wave transport equation and tested for the seas around the Indian subcontinent (5°S to 25°N latitude; 45°E to 100°E longitude). The grid averaged hindcast wave heights are found to be moderately matching with the GEOSAT altimeter measured significant wave heights of the 1987–1989 period, particularly for waves higher than 1 meter.
Volume 121 Issue 2 April 2012 pp 385-392
Wave hindcast experiments in the Indian Ocean using MIKE 21 SW model
P G Remya Raj Kumar Sujit Basu Abhijit Sarkar
Wave prediction and hindcast studies are important in ocean engineering, coastal infrastructure development and management. In view of sparse and infrequent
Volume 122 Issue 4 August 2013 pp 935-946
Low level cloud motion vectors from Kalpana-1 visible images
Inderpreet Kaur S K Deb C M Kishtawal P K Pal Raj Kumar
Till now low-level winds were retrieved using Kalpana-1 infrared (IR) images only. In this paper, an attempt has been made to retrieve low-level cloud motion vectors using Kalpana-1 visible (VIS) images at every half an hour. The VIS channel provides better detection of low level clouds, which remain obscure in thermal IR images due to poor thermal contrast. The tracers are taken to be 15 × 15 pixel templates and hence each wind corresponds to about 120km × 120km at sub-satellite point. Multiplet based wind retrieval technique is followed for VIS wind derivation. However, for height assignment of VIS winds, collocated IR image is used. Due to better contrast between cloud and ocean surface, the low level atmospheric flow is captured better as compared to IR winds. The validation of the derived VIS winds is done with Global Forecast System (GFS) model winds and Oceansat-II scatterometer (OSCAT) winds.
Volume 123 Issue 5 July 2014 pp 1075-1087
An assessment of wind forcing impact on a spectral wave model for the Indian Ocean
P G Remya Raj Kumar Sujit Basu
The focus of the present study is the assessment of the impact of wind forcing on the spectral wave model MIKE 21 SW in the Indian Ocean region. Three different wind fields, namely the ECMWF analyzed winds, the ECMWF blended winds, and the NCEP blended winds have been used to drive the model. The wave model results have been compared with
Volume 130 All articles Published: 9 February 2021 Article ID 0034 Research article
JAGDISH PRAJAPATI BIPASHA PAUL SHUKLA RAJ KUMAR
An objective wavelet based algorithm has been developed to find the orientation of rolls in Synthetic Aperture Radar (SAR) imagery using Radar Imaging Satellite (RISAT-1) data. The orientation of rolls plays a very crucial role for the estimation of ocean surface wind direction. It also affects the shape and size of a tropical cyclone. In this manuscript, SAR image was decomposed using Haar Wavelet Transform (HWT) and optimal thresholding was done to delineate the direction of propagating rolls. The roll features were found oriented in the range 26$^{\circ}$–31$^{\circ}$ from the along track direction. These features are very useful to retrieve wind direction and hence the vector wind observation over the ocean surface.
$\bf{Highlights}$
$\bullet$ Development of a new algorithm to find the orientation of MABL rolls in the SAR imagery.
$\bullet$ Use of Haar Wavelet Transform due to its high computational efficiency and ease of potential operational application.
$\bullet$ The study is first of its kind over the Indian Ocean.
$\bullet$ Rolls are oriented between 26$^{\circ}$ to 31$^{\circ}$ from the along track direction.
Volume 132, 2023
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