摘要:
从声波扰动介质中的电波波动方程出发，使用时域有限差分(FDTD)方法，结合声波传播的FDTD模型，构建了描述声波和电波相互作用的数值模型，并运用该模型分析风场和温度对无线电声波探测系统的探测高度的影响。数值模拟结果表明：温度与风场剖面的存在改变声波和电波散射回波的传播轨迹；温度梯度剖面主要影响声波的传播速度，风场剖面导致作为电波散射体的声波波阵面的偏移，降低电波散射回波的强度并改变回波路径，使得接收数据减少，限制无线电声波探测系统的探测高度；在强风背景下，若降低声波散射体高度，电波散射回波“聚束点”的偏移会有较大的改善，但同时意味着探测高度的降低。为了改善风场背景下无线电声波探测系统的探测高度，可以使用双基地雷达或者增大接收天线面积等方法来实现。
Abstract:
Radio acoustic sounding system (RASS) is a detection technique using the interaction between radio wave and acoustic wave to remotely measure vertical profiles of the atmospheric temperature, and usually composed of a Doppler radar with fixed beam (monostatic or bistatic) and an acoustic source with high power. By combining acoustic propaga-tion equation and radio wave propagation equation in a disturbance medium and using a finite-difference time-domain method, a numerical model describing the interaction between acoustic wave and electric wave is constructed, and the model is used to analyze the effects of wind and temperature on detection height of RASS. In the atmospheric tem-perature background, the propagations of a single frequency acoustic wave packet under different wind conditions are simulated, and the scattering propagation of electric wave packets corresponding to the acoustic scatterer are analyzed and compared. Besides, the entire physical process are described from the angle of energy density. The numerical simulation results show that the propagation trajectories of both acoustic wave and radio wave backscattering echo are changed due to the existence of wind field and temperature profile. The presence of wind field results in an offset of acoustic wave front, reducing the strength and changing the trajectory of radio wave backscattering echo, so that the detection height is limited due to the reduction of receiving data. The simulation results of the acoustic wave reveal that the temperature profile mainly affects the propagation velocity of acoustic wave, while the presence of wind field may result in shifts of propagation trajectory and acoustic wave front, and the greater the wind speed, the more the horizontal shift of acoustic wave front is. The numerical analyses of scattering propagations of radio wave with the acoustic scatterer at the same height under different background atmospheric conditions manifest that the stronger the wind speed, the more the deviation of electric wave echo from the receive antenna is, and the smaller the echo intensity is when the scattering echo propagates to the same position. The theoretical calculations with the acoustic wave scatterer at different heights under the same atmospheric wind field (strong wind) background demonstrate that if the height of scattering point is reduced, the offset of the scattering echo “bunching point” at the same altitude will be greatly improved and the intensity will be enhanced, but it also means the decline of detection height. In order to improve the detection height under the background of wind field, some methods are adopted, such as using a bistatic radar antenna or increasing the reception antenna area.
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