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<p>Free gas in natural aquatic sediments exists within discrete bubbles, which contribute to sediment destabilization and have implications for global warming. In this study, a micro-scale bubble model is used to characterize the shapes and sizes of methane bubbles in muddy aquatic sediments, governed by the mechanical properties of these muds. Building on this, a macro-scale bubble size distribution model was developed to determine the maximum equivalent spherical bubble size and cumulative gas content. An acoustic methodology, which examines the frequency-dependent reflection coefficient of sound from gassy sediments and reveals resonant behavior, was used to test the proposed model. Five acoustic measurements were conducted in Lake Kinneret, Israel, – one in 2016 and four in 2022 – at water depths ranging from 23 to 37&#xa0;m. The transmitted chirp signal swelling from 300&#xa0;Hz to a maximum of 15,000&#xa0;Hz, was received by a nearby vertical line array consisting of up to seven hydrophones positioned near the source. Frequency analysis of the recorded signal components – including both bottom and surface reflections as well as the reverberant coda – revealed a spectral notch around 2584&#xa0;Hz in 2016 and between 3027 and 4373&#xa0;Hz in 2022, depending on the measurement location. These notches correspond to a maximum equivalent spherical bubble diameter of 7.95&#xa0;mm in 2016 and 4.50–6.54&#xa0;mm in 2022. These results are consistent with direct measurements of bubble size distributions obtained through X-ray computed tomography of frozen sediment cores collected in Lake Kinneret in 2016 by another research group, at locations matching the acoustic experiment sites.</p>

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Determining bubble size in aquatic sediments using wideband acoustic resonance and a bubble size distribution model: testing and application in Lake Kinneret, Israel

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年9月26日

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  • E. Uzhansky,
  • R. Katsman,
  • A. Lunkov,
  • B. Katsnelson

摘要

Free gas in natural aquatic sediments exists within discrete bubbles, which contribute to sediment destabilization and have implications for global warming. In this study, a micro-scale bubble model is used to characterize the shapes and sizes of methane bubbles in muddy aquatic sediments, governed by the mechanical properties of these muds. Building on this, a macro-scale bubble size distribution model was developed to determine the maximum equivalent spherical bubble size and cumulative gas content. An acoustic methodology, which examines the frequency-dependent reflection coefficient of sound from gassy sediments and reveals resonant behavior, was used to test the proposed model. Five acoustic measurements were conducted in Lake Kinneret, Israel, – one in 2016 and four in 2022 – at water depths ranging from 23 to 37 m. The transmitted chirp signal swelling from 300 Hz to a maximum of 15,000 Hz, was received by a nearby vertical line array consisting of up to seven hydrophones positioned near the source. Frequency analysis of the recorded signal components – including both bottom and surface reflections as well as the reverberant coda – revealed a spectral notch around 2584 Hz in 2016 and between 3027 and 4373 Hz in 2022, depending on the measurement location. These notches correspond to a maximum equivalent spherical bubble diameter of 7.95 mm in 2016 and 4.50–6.54 mm in 2022. These results are consistent with direct measurements of bubble size distributions obtained through X-ray computed tomography of frozen sediment cores collected in Lake Kinneret in 2016 by another research group, at locations matching the acoustic experiment sites.