模垂直波束传输损失分析

海底反向散射矩阵的计算需要先知道模衰减系数和模函数．从实际数据中计算各阶模的衰减系数很困难且无必要．本文讨论了从模垂直波束(MVB)分析中提取分组平均模衰减系数的方法．波束形成输出谱由两部分组成：一部分是模能量加权求和，另一部分是模干涉和．如果模干涉项可以忽略，则分组平均模衰减系数可以从两个不同距离的波束形成器输出谱中求得．数值模拟导出了减小模干涉项的有效方法，并仿真了不同条件下分组平均模衰减系数的提取．同时还利用在2001年亚洲海实验(ECS)期间，由57m长垂直线阵采集的传输实验数据进行了分组平均模衰减系数的提取，模衰减系数的量级为10^-4,由此计算得到的Q值为1．4，对应于Hamilton分类的第6类海底，与实际测量的结果相符．

The modal-vertical-beam(MVB) transmission loss analysis

It is neccessary to know model attenuation and model function before the bottom back_scattering matrix is calculated.Extracting every modal attenuation from real data is difficult and unnecessary. In this paper, a method of extracting the group-averaged modal attenuation coefficient from the Modal-Vertical-Beam (MVB) analysis is discussed. The beamformer output spectrum consists of two parts: one is the modal energy weighted sum and another is the intermode interference sum. If the intermode term can be ignored, group-averaged-modal attenuation coefficient can be obtained from the beamformer output at two different ranges. Numerical simulations have been conducted to investigate the effective approaches for reducing the intermode term. Transmission loss data collected by a 57m VLA during the 2001 ASIAEX is also performed to extract the coefficient whose quantity is 10~(-4). Q calculated from the coefficient is 1.4, which is consistent with the measured result,corresponding to 6~(th) bottom of Hamilton.Now, Guest professor of the State Key Lab. of Ocean Acoustics