Water column imaging multibeam echo sounder systems (MBESs) are a promising technology for quantitative estimates of the gas bubble volume flow within large gas seepage areas. Considerable progress has been made in recent years toward applicable calibration methods for MBESs as well as developing inversion models to convert acoustically measured backscattering cross sections to gas bubble volume flow. However, MBESs are still not commonly used for quantitative gas flow assessments. A reason for this is the absence of published processing methods that demonstrate how MBES data can be processed to quantitatively represent bubble streams. Here, we present a novel method (echo grid integration) that allows for assessing the aggregated backscattering cross section of targets within horizontal water layers. This derived value enables quantifying bubble stream gas flow rates using existing acoustic inversion methods. The presented method is based on averaging geo-referenced volume backscattering coefficients onto a high-resolution 3D voxel-grid. The results are multiplied with the voxel volume to represent measurements of the total backscattering cross-section within each voxel cell. Individual gridded values cannot be trusted because the beam pattern effects cause the values of individual targets to “smear” over multiple grid-cells. The true aggregated backscattering cross-section is thus estimated as the integral over the grid-cells affected by this smearing. Numerical simulation of MBES data acquisition over known targets assesses the method's validity and quantify it's uncertainty for different, realistic scenarios. The found low measurement bias (< 1%), and dispersion (< 5%) are promising for application in gas flow quantification methods.

中文翻译：

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回波网格集成：一种预处理多波束水柱数据以量化水下气泡排放的新方法

水柱成像多波束回声测深系统（MBES）是一种有前途的技术，用于定量估计大型气体渗漏区域内的气泡体积流量。近年来，在适用于 MBES 的校准方法以及开发反演模型以将声学测量的反向散射截面转换为气泡体积流量方面取得了相当大的进展。然而，MBES 仍然不常用于定量气体流量评估。其原因之一是缺乏已发表的处理方法来演示如何处理 MBES 数据以定量表示气泡流。在这里，我们提出了一种新颖的方法（回波网格积分），可以评估水平水层内目标的聚合后向散射截面。该导出值使得能够使用现有的声学反演方法来量化气泡流气体流速。所提出的方法基于将地理参考体积反向散射系数平均到高分辨率 3D 体素网格上。结果乘以体素体积以表示每个体素单元内总反向散射横截面的测量值。单个网格值不可信，因为波束方向图效应导致单个目标的值“涂抹”在多个网格单元上。因此，真实聚合后向散射截面被估计为受该拖尾影响的网格单元上的积分。对已知目标的 MBES 数据采集的数值模拟评估了该方法的有效性，并量化了不同现实场景的不确定性。