Institut des Sciences de la Terre, Université Joseph Fourier, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5275, 1381 Rue de la Piscine, Saint-Martin d'Hères, France.
J Acoust Soc Am. 2011 Sep;130(3):1232-41. doi: 10.1121/1.3621271.
Acoustic tomography in a shallow ultrasonic waveguide is demonstrated at the laboratory scale between two source-receiver arrays. At a 1/1,000 scale, the waveguide represents a 1.1-km-long, 52-m-deep ocean acoustic channel in the kilohertz frequency range. Two coplanar arrays record the transfer matrix in the time domain of the waveguide between each pair of source-receiver transducers. A time-domain, double-beamforming algorithm is simultaneously performed on the source and receiver arrays that projects the multi-reflected acoustic echoes into an equivalent set of eigenrays, which are characterized by their travel times and their launch and arrival angles. Travel-time differences are measured for each eigenray every 0.1 s when a thermal plume is generated at a given location in the waveguide. Travel-time tomography inversion is then performed using two forward models based either on ray theory or on the diffraction-based sensitivity kernel. The spatially resolved range and depth inversion data confirm the feasibility of acoustic tomography in shallow water. Comparisons are made between inversion results at 1 and 3 MHz with the inversion procedure using ray theory or the finite-frequency approach. The influence of surface fluctuations at the air-water interface is shown and discussed in the framework of shallow-water ocean tomography.
在实验室规模上，在两个源-接收器阵列之间演示了浅层超声导波中的声层析成像。在 1/1000 的比例下，该波导代表了千赫兹频率范围内 1.1 公里长、52 米深的海洋声通道。两个共面阵列记录了波导中每对源-接收器换能器之间的传递矩阵的时域。在源和接收器阵列上同时执行时域双波束形成算法，将多反射声回波投影到等效的特征射线集合中，这些射线的特征是它们的传播时间以及它们的发射和到达角度。当在波导中的给定位置产生热羽流时，每 0.1 秒测量每个特征射线的传播时间差异。然后使用基于射线理论或基于衍射灵敏度核的两个正向模型进行传播时间层析成像反演。空间分辨距离和深度反演数据证实了浅水中声层析成像的可行性。在 1 和 3 MHz 之间比较了使用射线理论或有限频率方法的反演结果。在浅海海洋层析成像的框架内，展示和讨论了空气-水界面处表面波动的影响。
