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Vector Acoustic Analysis of Time-Separated Modal Arrivals From Explosive Sound Sources During the 2017 Seabed Characterization Experiment
IEEE Journal of Oceanic Engineering ( IF 4.1 ) Pub Date : 2020-01-01 , DOI: 10.1109/joe.2019.2902500 Peter H. Dahl , David R. Dall'Osto
IEEE Journal of Oceanic Engineering ( IF 4.1 ) Pub Date : 2020-01-01 , DOI: 10.1109/joe.2019.2902500 Peter H. Dahl , David R. Dall'Osto
The Intensity Vector Autonomous Recorder (IVAR) is a system that records four coherent channels of acoustic data continuously: one channel for acoustic pressure and three channels associated with a triaxial accelerometer from which acoustic particle velocity is obtained. IVAR recorded the vector acoustic field in broadband signals originating from Signal, Underwater Sound (SUS) (Mk-64) charges deployed at 5–13-km range from the fixed IVAR site (mean depth 74.4 m) as part of the 2017 Seabed Characterization Experiment (SBCEX) designed to study the acoustics of fine-grained muddy sediments. Sufficient geometric dispersion at these ranges permitted unambiguous identification of up to four modes as a function of frequency for frequencies less than 80 Hz. From time–frequency analysis of the dispersed arrivals, a single mode ($n$) and single-frequency ($f_{i})$ properties are identified at peaks in the narrowband scalar field, with time dependence corresponding to mode group speed. At these time–frequency addresses, four quantities derived from the vector acoustic measurements are formed by coherent combination of pressure and velocity channels: first, modal phase speed; second, circularity, a measure of the normalized curl of active intensity; third, depth-dependent mode speed of energy; and fourth, vertical component of reactive intensity normalized by scalar intensity. A means to compute these quantities theoretically is provided, and a comparison of model results based on a notional geoacoustic representation for the SBCEX experimental area consisting of a single low-speed mud layer over a half-space area versus a Pekeris representation based on the same half-space shows a striking difference, with the field observations also clearly at variance with the Pekeris representation. A fundamental property of mode 2, observed at the IVAR location, is a change in sign for circularity and vertical reactive intensity near 37 Hz that is posited as a constraint observation for mode 2 that must be exhibited by any geoacoustic model that includes a low-speed mudlike layer applied to this location.
中文翻译:
2017 年海底特征实验中爆炸声源时分离模态到达的矢量声学分析
强度矢量自主记录器 (IVAR) 是一种连续记录声学数据的四个相干通道的系统:一个通道用于声压,三个通道与三轴加速度计相关联,从中获得声学粒子速度。作为 2017 年海底表征的一部分,IVAR 在距固定 IVAR 站点(平均深度 74.4 m)5-13 公里范围内部署的信号、水下声波 (SUS) (Mk-64) 电荷产生的宽带信号中记录了矢量声场实验 (SBCEX) 旨在研究细粒泥质沉积物的声学。在这些范围内足够的几何色散允许明确识别多达四种模式作为频率低于 80 Hz 的频率的函数。从分散到达的时频分析,在窄带标量场的峰值处识别出单模 ($n$) 和单频 ($f_{i})$ 属性,其时间依赖性对应于模式群速度。在这些时频地址上,从矢量声学测量中导出的四个量是由压力和速度通道的相干组合形成的:首先,模态相位速度;第二,圆度,活动强度归一化卷曲的量度;第三,深度依赖模式的能量速度;第四,通过标量强度归一化的反应强度的垂直分量。提供了一种理论上计算这些量的方法,基于 SBCEX 实验区的概念地声表示的模型结果的比较(由半空间区域上的单个低速泥层组成)与基于相同半空间的 Pekeris 表示的比较显示出显着差异,其中现场观察也明显与 Pekeris 表示不同。在 IVAR 位置观察到的模式 2 的一个基本特性是在 37 Hz 附近圆度和垂直反应强度的符号变化,这被假定为模式 2 的约束观测,任何包含低-速度泥状层应用到这个位置。
更新日期:2020-01-01
中文翻译:
2017 年海底特征实验中爆炸声源时分离模态到达的矢量声学分析
强度矢量自主记录器 (IVAR) 是一种连续记录声学数据的四个相干通道的系统:一个通道用于声压,三个通道与三轴加速度计相关联,从中获得声学粒子速度。作为 2017 年海底表征的一部分,IVAR 在距固定 IVAR 站点(平均深度 74.4 m)5-13 公里范围内部署的信号、水下声波 (SUS) (Mk-64) 电荷产生的宽带信号中记录了矢量声场实验 (SBCEX) 旨在研究细粒泥质沉积物的声学。在这些范围内足够的几何色散允许明确识别多达四种模式作为频率低于 80 Hz 的频率的函数。从分散到达的时频分析,在窄带标量场的峰值处识别出单模 ($n$) 和单频 ($f_{i})$ 属性,其时间依赖性对应于模式群速度。在这些时频地址上,从矢量声学测量中导出的四个量是由压力和速度通道的相干组合形成的:首先,模态相位速度;第二,圆度,活动强度归一化卷曲的量度;第三,深度依赖模式的能量速度;第四,通过标量强度归一化的反应强度的垂直分量。提供了一种理论上计算这些量的方法,基于 SBCEX 实验区的概念地声表示的模型结果的比较(由半空间区域上的单个低速泥层组成)与基于相同半空间的 Pekeris 表示的比较显示出显着差异,其中现场观察也明显与 Pekeris 表示不同。在 IVAR 位置观察到的模式 2 的一个基本特性是在 37 Hz 附近圆度和垂直反应强度的符号变化,这被假定为模式 2 的约束观测,任何包含低-速度泥状层应用到这个位置。