Acoustic propagation in gassy intertidal marine sediments: An experimental study

Abstract

The need to predict acoustic propagation through marine sediments that contain gas bubbles has become increasingly important for civil engineering and climate studies. There are relatively few in situ acoustic wave propagation studies of muddy intertidal sediments, in which bubbles of biogenic gas (generally methane, a potent greenhouse gas) are commonly found. We used a single experimental rig to conduct two in situ intertidal acoustical experiments to improve understanding of acoustic remote sensing of gassy sediments, eventually including gas bubble size distributions. In the first experiment, we measured sediment sound speed and attenuation between four aligned hydrophones for a quasi-plane wave propagating along the array. The second experiment involved a focused insonified sediment volume created by two transducers emitting coincident sound beams at different frequencies that generated bubblemediated acoustic signals at combination frequencies. The results from sediment core analyses, and comparison of in situ acoustic velocity and attenuation values with those of water-saturated sediments, together provide ample evidence for the presence of in situ gas bubbles in the insonified volumes of sediments. These datasets are suitable for linear and non-linear inversion studies that estimate in situ greenhouse gas bubble populations, needed for future acoustical remote sensing applications.

Probing the pressure dependence of sound speed and attenuation in bubbly media: Experimental observations, a theoretical model and numerical calculations

“…For imaging applications β 0 would be 3.6-7.2×10 −7 inside blood. In our study the concentration of MBs was 6.3×10 4 MBs/mL with β 0 of ≈ 5.1 ×10 −6 . Thus, the void fraction in our work is relevant to clinical therapeutic applications of the UCAs in blood.…”

“…Each R 0i has a number density of N i . These 63 MBs were distributed randomly in a cube of diameter 0.1cm to simulate the total concentration of 6.3×10 4 MBs/mL in the experiments. The total gas volume in the experiments was ≈5.1×10 −12 m 3 /mL.…”

“…This provides important advantages to applications in underwater acoustics and acoustic characterization of contrast agents. In the measurements related to the gassy intertidal marine sediments, pressures in the range of 15-20kPa are used 4 . The bubble size range is between 80µm to 1mm 2,4,100 .…”

“…Acoustically excited microbubbles (MBs) are present in a wide range of phenomena; they have applications in sonochemistry 1 ; oceanography and underwater acoustics [2][3][4] ; material science 5 , sonoluminescence 6 and in medicine 7,8,[10][11][12][13][14] . Due to their broad and exciting biomedical applications, MBs have many emerging applications in diagnostic and therapeutic ultrasound 14 .…”

Size quantification of non-spherical bubbles by ultrasound

“…1 引言 液体中气泡在生物应用、渔业科学、工业选矿、纸浆生产及声空化等工程和 环境应用中至关重要. 如在深水盆地和大陆边缘等地质环境中进行水下甲烷气 体泄露监测 [1,2] , 工业选矿中利用气泡大小分布监测浮选过程 [3,4] , 复合材料 [5,6] 或 推进剂 [7] 生产中对气泡是否混入及气泡含量进行监测以提高质量; 造纸工序中 O 2 泡大小分布是决定纸浆脱木素环节是否顺利进行 [8] 的关键. 气泡表征常用方法有光学和声学两类.…”