O.N. Kiselev - Ph.D. (Eng.), Associate Professor, Senior Research Scientist, Tomsk State University of Control Systems and Radioelectronics G.S. Sharygin - Dr.Sc. (Eng.), Professor, Tomsk State University of Control Systems and Radioelectronics M.V. Krutikov - Head of Laboratory, Tomsk State University of Control Systems and Radioelectronics E-mail: gssh@mail.tomsknet.ru

Estimation of VHF-signals characteristics beyond the radio horizon using meteorological data is one of most important problems of passive radar exploitation. Solving this problem is necessary for operative and perspective planning of activity at the particular regions of the ocean. TUCSR Radio System Research Institute performed many years research meant to work out the procedure of VHF signals characteristics diagnosis and prognosis a priory using known and measured parameters of troposphere in the central part of the Pacific ocean. In particular, there was worked out the regional procedure of the statistical multiplier of signals, received by ship and costal radars, estimation. The results of the activity are presented by maps in «Radio climatic troposphere atlas of the Pacific ocean», published in 2000. The maps allow to make the a priory prognoses of the average monthly signal level correcting the standard function of attenuation averaged over all seasons and all regions of the Ocean. In order to take into account the season variation at some particular regions the standard function of attenuation is added with the region-time correction shown in the maps by isolines over the whale surface of the Pacific Ocean. Study of the mesoscale signal fluctuations allowed to suggest the procedure of shorted prognoses by taking into consideration the statistical relation between the attenuation factor hour averaged and corresponding parameters of atmosphere heterogeneity measured by the existing meteo- and aero-devices. Radio physical and meteorological processes under consideration are presented as a sum of non-random functions describing a priory variation of the signal and meted parameters and random correction with zero average. Distribution of this correction probability is Gaussian with diminished influence of cyclic variations. In order to take into account the meteorological dependence of the attenuation factor there is used apparatus of multiplied regress analysis. The attenuation factor is presented as a sum of the non-random function (the norm), describing the month average function for some particular season and ocean region, and the deviation, depending on the meteorological condition of the moment. Such estimation describes well hour average attenuation factor and is calculated using a priory known norms of the signal and meteorological parameters, known coefficients of regression and the measured meteorological parameters. The efficient estimation of the attenuation factor hour average, found by this method, can have the root-mean-square error from 7-11 dB to 4-5 dB depending on the region of the Ocean and the number of meteorological parameters used. A priory data, concerning the attenuation factor (the norms), needed for the prognoses ate given in the Atlas of the Pacific Ocean (mentioned above). There is no information for other regions. Still these norms can be found using ground or water based data for troposphere refraction index. Using the Atlas data and the suggested procedure for calculation the attenuation function in the far troposphere propagation zone, as well as the known procedure for calculation in the zones of interference and diffraction, one can calculate the distance to the working source of illumination if one knows the calculated dependence of the received signal on the distance. In addition to the distance one can estimate characteristics of the illuminated signal source and in case of the active radar the maximal distance of the target with known effective dispersion surface detection.

 

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