Measurement of forward scattering coefficient of different water bodies at different frequencies

Abstract

The thrust of this study is to analyse the effect of scattering of electromagnetic waves on microwave links and tracking of low flying objects in the presence of strong ground bounce return from water bound areas. <span style="mso-bidi-font-weight:bold">For this purpose, a ground based bi-static forward scatterometer has been used to generate co-polarized specular data at CJ, X, and Ku bands. The measurements are carried out on three types of water surfaces, i.e. tap water, natural lake water and saline water. All the three water surfaces are assumed to be slightly rough surfaces at the frequency of interest. Therefore, small perturbation model of slightly rough surface for forward scattering is a good selection to analyse data. The scattered microwave power from the terrain measured for 25° - 70° scattering angle (<i><img src='/image/spc_char/theta.gif' border=0>_s</i>) with an interval of 5° in specular direction with transmitting antenna placed at an incidence angle (<i><img src='/image/spc_char/theta.gif' border=0>_i</i>) of 45° from nadir illuminates the terrain keeping <i><img src='/image/spc_char/phi.gif' border=0>_i</i> = <i><img src='/image/spc_char/phi.gif' border=0>_s</i> = 0° at 5.825, 9.472 and 13.4 GHz in CJ, X and KU bands, respectively for <i style="mso-bidi-font-style:normal">vv</i> and <i style="mso-bidi-font-style:normal">hh</i> polarization with different antenna heights. The forward scattering coefficient computed with the help of experimental geometry parameters, which then compared with estimated value of scattering coefficient <span style="font-family:Times-Bold;mso-bidi-font-family: Times-Bold;mso-bidi-font-weight:bold" lang="EN-GB">obtained from small perturbation model of slightly rough surface.<span style="font-family:Times-Bold;mso-bidi-font-family:Times-Bold;mso-bidi-font-weight: bold" lang="EN-GB"> A good agreement between observed and estimated scattering coefficient for horizontal (<i>hh</i>) and vertical (<i>vv</i>) polarization has been found in X and KU bands with a polarization reversal in CJ band. It is also observed that dissolved salt or impurities increase the value of scattering coefficient. The basic purpose of this study is to map and monitor the natural resources and to provide timely inputs for the planners to develop appropriate strategies for optimum utilisation of the resources.

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