Geoacoustic parameter variations and inversion estimates with a silt-suspension theory of mud

Abstract

Marine mud sediments can be modeled by a recent silt-suspension theory [Pierce, et al., JASA, 142, 2591 (2017) (A)], in which silt particles are embedded in a suspension of flocculated clay particles. This presentation investigates the influence on attenuation predictions from uncertainties in parameters such as the effective grain density and the distribution of grain sizes. For example, the matrix of clay flocs may effectively lower the density of silt grains and cause decreased attenuation. Effects from such parameters are determined on the regime where attenuation is nearly linear with frequency. The value of porosity is critical for specifying sound speed and attenuation in the mud layer. Porosity measurements from sediment cores can have significant uncertainty, particularly in the upper region, from the core extraction process. Inversions for porosity and other physical parameters of the silt-suspension theory are performed along a WHOI AUV track from the 2017 Seabed Characterization Experiment. Characteristics of cores guide parameter modeling and ranges for the inversions. This approach produces estimates of sound speed, attenuation, and density that are related by physical constraints. In addition, the approach allows for validity assessment of current geoacoustic mud models using measured data. [Work supported by ONR.]Marine mud sediments can be modeled by a recent silt-suspension theory [Pierce, et al., JASA, 142, 2591 (2017) (A)], in which silt particles are embedded in a suspension of flocculated clay particles. This presentation investigates the influence on attenuation predictions from uncertainties in parameters such as the effective grain density and the distribution of grain sizes. For example, the matrix of clay flocs may effectively lower the density of silt grains and cause decreased attenuation. Effects from such parameters are determined on the regime where attenuation is nearly linear with frequency. The value of porosity is critical for specifying sound speed and attenuation in the mud layer. Porosity measurements from sediment cores can have significant uncertainty, particularly in the upper region, from the core extraction process. Inversions for porosity and other physical parameters of the silt-suspension theory are performed along a WHOI AUV track from the 2017 Seabed Characterization Experiment. Ch...