Distortion of acoustic wave caused by nonlinear propagation transfers acoustic energy into higher harmonics of the transmitted signal. When operating several broadband echosounders with non-overlapping frequency bands to cover a wide frequency range, higher harmonics generated by one band may interfere with the fundamental band of others. This interference (i.e., crosstalk) can adversely affect the measured backscattered amplitude frequency response and in some circumstances, appears as spurious targets above and/or below the main target in pulse-compressed echograms. The nonlinear propagation of frequency-modulated acoustic waves in a directional beam was modeled and used to assess methods to reduce the deleterious effects of harmonic components in the signal, and was also compared to field experiments using the seabed echo and a metallic target sphere, with good agreement. Two methods are shown to materially reduce crosstalk: (1) reduction in transmit power, which reduces crosstalk amplitude by a larger amount than the associated reduction in transmit power, and (2) selection of a proper Fourier window length in the processing stage. The effect of crosstalk was small (<0.4 dB or 10%) for area backscattering measurements, but could be several dB for target strength measurements at different frequencies, depending on the transmit signals and processing parameters.

中文翻译：

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宽带多通道回声测深仪中的非线性串扰

非线性传播引起的声波失真会将声能转换为传输信号的高次谐波。当使用具有不重叠频带的多个宽带回波测深仪来覆盖较宽的频率范围时，一个频带产生的高次谐波可能会干扰其他频带的基波。这种干扰（即串扰）可能会对测得的反向散射振幅频率响应产生不利影响，并且在某些情况下，在脉冲压缩回波图中显示为主要目标上方和/或下方的杂散目标。对调频声波在定向波束中的非线性传播进行了建模，并用于评估减少信号中谐波分量的有害影响的方法，并与使用海底回波和金属目标球体进行的野外实验进行了比较，吻合得很好。已显示出两种方法可从根本上减少串扰：（1）降低发射功率，与相关的发射功率降低相比，降低串扰幅度的幅度更大；（2）在处理阶段选择适当的傅立叶窗长度。对于区域反向散射测量，串扰的影响很小（<0.4 dB或10％），但是对于不同频率下的目标强度测量，串扰的影响可能是几dB，具体取决于发射信号和处理参数。（2）在处理阶段中选择适当的傅立叶窗口长度。对于区域反向散射测量，串扰的影响很小（<0.4 dB或10％），但是对于不同频率下的目标强度测量，串扰的影响可能是几dB，具体取决于发射信号和处理参数。（2）在处理阶段中选择适当的傅立叶窗口长度。对于区域反向散射测量，串扰的影响很小（<0.4 dB或10％），但是对于不同频率下的目标强度测量，串扰的影响可能是几dB，具体取决于发射信号和处理参数。