Abstract
Introduction. Doppler spectra of signals which are scattered from sea surface and received by radar is used in oceanology and ecological monitoring applications. Existing models of Doppler spectra have the limitation of application because they are based on empirical data in changing conditions. Variability of the observation conditions critically influence on microwaves scattering by sea surface at low grazing angles which is typical for marine radiolocations. Objective. The goal of investigation proposed in this article is to develop the mathematical model of Doppler spectra at low grazing angles for microwave frequency range. Materials and methods. The two-dimensional problem of the scattering of an electromagnetic field on a cylindrical deterministic surface is considered. For generating of sea surface realizations is used linear model with spatial sea spectrum Elfohaily. The solution of the scattering problem is obtained for the case of vertical polarization of the incident electromagnetic field by the method of an integral equation with the control of the error of the solution. The mathematical modeling of the Doppler Spectrum of signal scattered by sea surface is produced by method of statistical trial. The case where the direction of the observation of the sea surface by radar is perpendicular to the direction of the wind is considered. The electromagnetic filed scattered in the direction of the radar receiver as a function of time is calculated for each generated sea surface realizations. Further, the set of variables of the implementation of scattered field is calculated for implementation of the Doppler spectrum. Results. The set of implementations of the Doppler spectrum provided its mathematical model with consist of deterministic and random component. The approximation of each aforesaid component is suggested and mathematical expressions for value component calculation are presented. The analyze of modeling result is produced. Conclusion. The developed mathematical model is offered to use for the design of algorithm sea surface condition estimation and pollutant detection using the signal which received by radar.
Highlights
Doppler spectra of signals which are scattered from sea surface and received by radar is used in oceanology and ecological monitoring applications
Improved numerical simulation of electromagnetic wave scattering from perfectly conducting random surfaces // IEE proc. – microwave antennas propagation. 1997
High-Efficiency numerical computing in low-grazing scattering from sea surface using resistive tapering and forward-backward method // 3rd Asia-Pacific Conference on Antennas and Propagation
Summary
Вид шероховатой поверхности и характеризующие задачу геометрические характеристики показаны на рис. 1. Источник и приемник электромагнитной волны расположены в точке A. Ось 0Z системы координат перпендикулярна плоскости падения электромагнитной волны. Выбор вертикальной поляризации падающего поля обоснован тем, что работа РЛС на указанной поляризации обеспечивает большее по сравнению с горизонтальной поляризацией значение удельной эффективной площади рассеяния морской поверхности при скользящем облучении и наиболее часто используется в морских РЛС, выполняющих океанологические исследования [16]. Для построения численного решения интегрального уравнения оно сводится к системе линейных алгебраических уравнений (СЛАУ) с неизвестными, представляющими собой коэффициенты разложения искомого решения по выбранным базисным функциям [17]–[18]. При решении сгенерированная реализация морской поверхности разбивается на N сегментов, в пределах каждого из которых для представления искомого решения (плотности поверхностного тока) используется кусочно-постоянная базисная функция. В настоящей статье для решения задачи рассеяния использовано интегральное уравнение (2); аналогичное решение можно также получить, используя (1). Элементы матрицы импеданса при вертикальной поляризации вычислялись по формулам [17], [20]
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