Estimation and validation of sediment properties by normal-incidence echosounder

Abstract

Broad implementation of normal-incidence echo sounding has generated a need for sediment characterization models. These models may utilize the magnitude, phase, and/or envelope shape of reflected acoustic waveforms to infer physical, geoacoustic, and engineering properties of ocean sediment. Normal-incidence echo soundings enable the remote survey of vast underwater areas at a fraction of the cost of ground truth sampling methods, i.e., cores and grabs. In collaboration with the Dauphin Island Sea Lab, acoustic data was collected in the Petit Bois Pass off of the Alabama coast. The magnitude, pulse width, and skew ratio of the matched filter output were measured and quantified as bottom loss, full-width at half-max, and the ratio of half-width at half-max, respectively. Bottom loss measurements were used to determine the index of impedance which, through the application of empirically based regression equations, was then used to calculate sound speed ratio, density, mean grain size, and porosity of the sediment along the survey track. The estimated values of sediment properties are generally in agreement with those measured in the laboratory by ground truth survey. [Work supported by the Office of Naval Research, Ocean Acoustics.]Broad implementation of normal-incidence echo sounding has generated a need for sediment characterization models. These models may utilize the magnitude, phase, and/or envelope shape of reflected acoustic waveforms to infer physical, geoacoustic, and engineering properties of ocean sediment. Normal-incidence echo soundings enable the remote survey of vast underwater areas at a fraction of the cost of ground truth sampling methods, i.e., cores and grabs. In collaboration with the Dauphin Island Sea Lab, acoustic data was collected in the Petit Bois Pass off of the Alabama coast. The magnitude, pulse width, and skew ratio of the matched filter output were measured and quantified as bottom loss, full-width at half-max, and the ratio of half-width at half-max, respectively. Bottom loss measurements were used to determine the index of impedance which, through the application of empirically based regression equations, was then used to calculate sound speed ratio, density, mean grain size, and porosity of the se...