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Communication Dans Un Congrès Année : 2017

Acoustic measurement of suspended sediments in rivers: potential impact of air micro-bubbles?

Mesure acoustique des sédiments en suspension dans les rivières : impact potentiel des micro-bulles d'air?

A. Vergne
  • Fonction : Auteur
Céline Berni
J. Le Coz
  • Fonction : Auteur

Résumé

Following the success of Acoustic Doppler Current Profiler (ADCP) technology for measuring river discharge, there has been a growing interest in the last decade in extracting information on river suspended sediment fluxes from acoustic backscatter data. Despite the efforts to find a relationship between suspended sediment concentration (SSC) and backscatter, an inversion technique applicable to vertical river backscatter profiles is still missing. The theoretical and empirical bases of such techniques have been originally developed for ocean bottom suspended sediment monitoring. As a first step in our attempt to adapt these models to rivers, we measured the acoustic response of a usual glass beads suspension in a tank. Unsurprisingly, the acoustic model agrees quite well with the measurements as soon as the effect of air micro-bubbles is limited. As a second step, we deployed an acoustic backscatter profiler in the Rhône River (France) in very clear water conditions (SSC < 10 mg/l). The recorded acoustic intensities were stronger than expected at low frequency, suggesting that other scatters may contribute to the recorded echo. Typical river sediment suspensions are expected to produce weak backscatter signal, especially at common ADCP frequencies, due to small particle sizes (Rayleigh regime) and relatively low concentrations. In such conditions, the impact of air micro-bubbles - generally neglected at the bottom of the ocean - could be relevant in rivers. This preliminary work calls for further investigation to assess the potential impact of nonsediment scatterers on acoustic backscatter when trying to measure SSC with sonar technologies in rivers.
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Dates et versions

hal-01768427 , version 1 (17-04-2018)

Identifiants

Citer

A. Vergne, Céline Berni, J. Le Coz. Acoustic measurement of suspended sediments in rivers: potential impact of air micro-bubbles?. Underwater Acoustics Conference and Exhibition 2017, Sep 2017, Skiathos, Greece. pp.749-754. ⟨hal-01768427⟩

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