Abstract Remote sensing is a desirable method for measuring ocean currents on various spatial and temporal scales. Coastal acoustic tomography (CAT) can measure current velocity in coastal and shallow seas, but the application of this method in stratified shallow estuaries has not been sufficiently tested. This study revisits the acoustic transmission data obtained from the 2013 Hiroshima Bay CAT experiment and investigates what information could be obtained from acoustic data when a relatively strong southward wind blew in the bay. We determined path-averaged currents of the first arrival rays and compared the temporal variations in this path-averaged current with those in the wind, water temperature, and detided sea level. When the southward wind was intensifying, the sea level at the northern coast of the bay decreased and then recovered when the southward wind subsided. These sea level variations must be accompanied by net volume transport variations. When sea level was recovering, the path-averaged current exhibited a positive bias, reflecting an increase of volume transport toward the inner part of the bay. In contrast, the path-averaged current did not show a noticeable variation when the sea level was decreasing although the surface layer current was expected to be intensified southward. This is because the first arrival ray did not propagate through the surface layer during the period, and therefore, the path-averaged current from the first arrival rays did not contain surface current velocity information. CAT is promising method for measuring variations in current velocity fields associated with winds; however, in the application to stratified and shallow estuaries such as Hiroshima Bay, it is crucial to consider acoustic ray-path variations when analyzing and interpreting travel time data time series.

中文翻译：

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重温广岛湾沿海声学断层扫描实验：路径平均海流的时间变化及其与风的关系

摘要 遥感是测量各种时空尺度洋流的理想方法。海岸声层析成像 (CAT) 可以测量沿海和浅海的流速，但该方法在分层浅海河口中的应用尚未得到充分测试。本研究重新审视了从 2013 年广岛湾 CAT 实验中获得的声学传输数据，并调查了当相对强的南风吹过海湾时，可以从声学数据中获得哪些信息。我们确定了初至射线的路径平均电流，并将该路径平均电流的时间变化与风、水温和确定的海平面的时间变化进行了比较。当南风渐强时，海湾北部海岸的海平面下降，然后在南风减弱后恢复。这些海平面变化必须伴随着净运输量变化。当海平面恢复时，路径平均电流表现出正偏差，反映了向海湾内部输送的体积增加。相比之下，尽管预计表层电流会向南加强，但当海平面下降时，路径平均电流并没有表现出明显的变化。这是因为在此期间，初至射线没有传播穿过表层，因此，初至射线的路径平均电流不包含表面流速度信息。CAT 是一种很有前途的方法，用于测量与风相关的当前速度场的变化；然而，在应用于广岛湾等分层和浅水河口的应用中，在分析和解释旅行时间数据时间序列时考虑声射线路径变化至关重要。