Modern multibeam echosounders (MBE) employ frequency-division techniques (FDT) to ensonify multiple sectors within the same ping cycle. This leads to improved performance in coverage rate, and yaw and pitch stabilization. However, it introduces a bias among sectors because MBES systems are frequency dependent. It also reduces the maximum pulse bandwidth compared to a single-sector sonar. In this study, we consider the code-division technique (CDT) as a solution to this problem. A set of orthogonal coded pulses are received within the same frequency band, and each sector is separated with a matched filter. We assess the feasibility of the technique through two stages. 1) First, we formulate an analytical model describing the power and crosstalk budgets of any multisector MBES. The model can then be used to design transmission sequences fitting these budgets. 2) Then, we display the practical usage of the technique for MBES imaging and mapping through simulated case studies. For the same total time-bandwidth budget, we compare the performance of FDT, CDT, and multicarrier CDT (MC-CDT), a hybrid method employing CDT and FDT, which is robust to strong dynamic backscatter. This study considers only bottom detection based on signal amplitude. Our results show that it is possible to share a larger frequency bandwidth between multiple sectors while maintaining an acceptable bottom detection performance similar to FDT. Our choice of time-bandwidth product with CDT offers a crosstalk suppression of −25 dB between sectors, but may display low-magnitude residual artefacts in the water-column data. MC-CDT provides a significant gain of pulse bandwidth while it offers interband separation performance comparable to FDT and reduces significantly the water-column artefacts.

中文翻译：

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具有正交波形的多波束回声测深仪：可行性和潜在优势


现代多波束回声测深仪 (MBE) 采用频分技术 (FDT) 在同一 ping 周期内对多个扇区进行声波探测。这会提高覆盖率、偏航和俯仰稳定性方面的性能。然而，它在扇区之间引入了偏差，因为 MBES 系统与频率相关。与单扇区声纳相比，它还降低了最大脉冲带宽。在本研究中，我们考虑使用码分技术（CDT）来解决这个问题。在同一频带内接收一组正交编码脉冲，并且每个扇区用匹配滤波器分开。我们通过两个阶段评估该技术的可行性。 1) 首先，我们制定一个分析模型来描述任何多扇区 MBES 的功率和串扰预算。然后可以使用该模型来设计适合这些预算的传输序列。 2）然后，我们通过模拟案例研究展示了MBES成像和绘图技术的实际应用。对于相同的总时间带宽预算，我们比较了 FDT、CDT 和多载波 CDT (MC-CDT) 的性能，MC-CDT 是一种采用 CDT 和 FDT 的混合方法，对强动态反向散射具有鲁棒性。本研究仅考虑基于信号幅度的底部检测。我们的结果表明，可以在多个扇区之间共享更大的频率带宽，同时保持类似于 FDT 的可接受的底部检测性能。我们选择的带有 CDT 的时间带宽产品可在扇区之间提供 −25 dB 的串扰抑制，但可能会在水柱数据中显示低量级的残留伪影。 MC-CDT 提供了显着的脉冲带宽增益，同时提供与 FDT 相当的带间分离性能，并显着减少了水柱伪影。