Acoustic wave propagation in rivers: an experimental study
<p>This research has been conducted to develop the use of passive acoustic monitoring (PAM) in rivers, a surrogate method for bedload monitoring. PAM consists in measuring the underwater noise naturally generated by bedload particles when impacting the river bed. Monitored bedload acoustic sig...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-06-01
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| Series: | Earth Surface Dynamics |
| Online Access: | https://www.earth-surf-dynam.net/7/537/2019/esurf-7-537-2019.pdf |
| Summary: | <p>This research has been conducted to develop the use of
passive acoustic monitoring (PAM) in rivers, a surrogate method for bedload
monitoring. PAM consists in measuring the underwater noise naturally
generated by bedload particles when impacting the river bed. Monitored
bedload acoustic signals depend on bedload characteristics (e.g., grain size
distribution, fluxes) but are also affected by the environment in which the
acoustic waves are propagated. This study focuses on the determination of
propagation effects in rivers. An experimental approach has been conducted
in several streams to estimate acoustic propagation laws in field
conditions. It is found that acoustic waves are differently propagated
according to their frequency. As reported in other studies, acoustic waves
are affected by the existence of a cutoff frequency in the kilohertz region. This cutoff frequency is inversely proportional to the water depth: larger water depth enables a better propagation of the acoustic waves at low frequency.
Above the cutoff frequency, attenuation coefficients are found to increase
linearly with frequency. The power of bedload sounds is more attenuated at
higher frequencies than at low frequencies, which means that, above the
cutoff frequency, sounds of big particles are better propagated than sounds
of small particles. Finally, it is observed that attenuation coefficients
are variable within 2 orders of magnitude from one river to another.
Attenuation coefficients are compared to several characteristics of the
river (e.g., bed slope, surface grain size). It is found that acoustic waves
are better propagated in rivers characterized by smaller bed slopes. Bed
roughness and the presence of air bubbles in the water column are suspected
to constrain the attenuation of acoustic wave in rivers.</p> |
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| ISSN: | 2196-6311 2196-632X |