Sea-trial results indicate that a stable interference structure can be observed in low frequency continuous spectra sound field. The equation of the interference striation is derived by using the concept of waveguide invariant and shows that the striations are a set of quasi hyperbolas. Some parameters, such as heading angle (ψ), waveguide invariant β and r0/V ( r0 is the range of the closest point of approach and v is the target velocity) can be estimated after image processing of the LOFAR gram and bearing-time history using Hough transform. Furthermore, four methods of passive ranging based on double elements model are proposed. The simulation results show that the first algorithm should be adopted in the target heading angle less than 10°; otherwise, the latter three algorithms have to be used to range, and the larger the heading angle is, the higher the ranging accuracy is. The relative ranging errors of four methods are all less than 10％.%海试验证了低频连续谱声场确实存在稳定可观察的干涉结构,结合波导不变量的概念推导了低频连续谱干涉条纹方程,干涉条纹为一族类双曲线.采用Hough变换对LOFAR图和瀑布图进行了图像处理,实现了目标航向角Φ、波导不变量β、r0/v(r0为目标最近通过距离,v为目标航行速度)等参数的估计;进而,基于双阵元模型,理论推导了4种被动测距算法.仿真研究表明:在航向角小于10°时,须采用算法1;航向角大于10°时,应采用后3种测距算法,并且测距精度基本随航向角增大而增高,相对测距误差均小于10%.
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