Geoacoustic inversion for gassy sediment parameters using reflection and scattering of acoustic signals

Results of experimental study and theoretical modeling of acoustic propagation and reverberation in Lake Kinneret (Israel) with gassy sediments are presented. The presence of methane bubbles in sediments significantly influences reflection and scattering of sound signals from the bottom, which in turn allows estimating properties of sediment using acoustic sensing. Experiments were carried out using R/V Hermona with sound source located at a 7 m depth radiating 1 s-long 0.3–7 kHz LFM sweeps with intervals from 1 to 20 s. Acoustic pressure time series were received on a single hydrophone at ∼1 m from the source and two vertical arrays fixed in the lake center at either 40 m or 10 m from each other. Analysis of both monostatic and bistatic experimental data (including long range propagation) was aimed to estimate acoustic characteristics of the bottom and then to infer the related gas content and its spatial and temporal variability. The sound speed in sediments at different locations (with different depth of water layer, maximal depth 40 m) was estimated to be ∼170–250 m/s that corresponds to gas volume concentrations ∼1%, which is in accordance with direct measurements made using non-acoustic probes. [Work was supported by BSF grant 2018150.]