• P C Pandey

      Articles written in Journal of Earth System Science

    • Capability ofBhaskara SAMIR to distinguish atmospheric water vapour and liquid water contents

      P C Pandey A K Sharma B S Gohil

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      An environmental model to compute microwave brightness temperatures for downward looking radiometers on board satellite is described. The effects of water vapour, oxygen and clouds on the brightness temperature have been studied for frequencies from 5 to 50 GHz for a standard tropical atmosphere. The effect of look angle on brightness temperture has also been investigated. Based on the model it has been shown that while the radiometers on boardBhaskara at 19·35 and 22·235 GHz are capable of giving the atmospheric water vapour and liquid water contents, the ability to distinguish these quantities is more for the combination of the frequencies 22·235 and 31 GHz.

    • A simulation technique for the determination of atmospheric water content with Bhaskara satellite microwave radiometer (SAMIR)

      P C Pandey A K Sharma B S Gohil

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      A simulation technique has been developed to estimate the integrated atmospheric water content over oceans using the 19·35 and 22·235 GHz brightness temperature data from satellite microwave radiometer (SAMIR) on board the Indian satellite Bhaskara. The results obtained have been compared with those from linear statistical regression and empirical methods as well as from the nearest radiosonde observations. Based on the simulation method, a map of total precipitable water for some of the Bhaskara passes in July 1980 over Bay of Bengal is given. The possible applications of such maps in the study of Indian summar monsoon and boundary layer characteristics have been pointed out.

    • Atmospheric temperature profile for a tropical region from TIROS-N microwave sounding unit

      B S Gohil A K Sharma P C Pandey

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      Atmospheric temperature profiles have been derived using 53·74 GHz, 54·96 GHz and 57·95 GHz channels data from the Microwave Sounding Unit onboard TIROS-N. For this purpose regression coefficients have been derived using MONEX-79 radiosonde data during the period May to July 1979. The temperature profiles derived at a few selected places were closer to radiosonde profiles than the profiles derived using standard regression coefficients for the tropical region supplied by NOAA.

    • The effect of whitecaps and foam on wind speed extraction with a pulse limited radar altimeter

      R M Gairola P C Pandey

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      The effect of whitecaps and foam on wind speed extraction with a pulse limited radar altimeter has been studied using a specular point model. By modelling foam and water as a two-layer media, we have investigated the changes in reflectivity as a function of thickness using electro-magnetic field theory. Our analysis indicated a change of reflectivity from a value of 0.617 at 13.9 GHz normal incidence to a value of 0.10 for a foam thickness of less than 1 cm. The values of reflectivity computed from a two-layer model compared fairly well with these derived using an emissivity model.

      The modified specular point model gave an improved relationship between σo and wind speed in comparison to Brown’s model. The Seasat altimeter’s data analysis over the Arabian sea and the Bay of Bengal gave an rms difference of 2.2 m/sec in wind speed retrieval using the present modified model and Brown’s model.

    • The variational technique of data assimilation using adjoint equations in a shallow water model

      Sujit Basu V Subramanian P C Pandey

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      The variational technique of data assimilation using adjoint equations has been illustrated using a nonlinear oceanographic shallow water model. The technique consists of minimizing a cost function representing the misfit between the model and the data subject to the model equations acting as constraints. The problem has been transformed into an unconstrained one by the use of Lagrange multipliers. Particular emphasis has been laid on finite difference formulation of the algorithm. Several numerical experiments have been conducted using simulated data obtained from a control run of the model. Implications of this technique for assimilating asynoptic satellite altimeter data into ocean models have been discussed.

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