Variability in normal-incidence acoustic response in shallow-water marine sediments

• Acoustic variability at 30 kHz is similar for all sediments in this data set.
• Acoustic coefficient of variability (CoV) at 50 kHz is quite distinct from 30 kHz.
• Sediment textural variability correlates with changes in acoustic CoV
• Silt variability correlates with CoV for high-percent sands.
• Sand and water content variability correlates with CoV for silty-clay.

Lateral variations in mass properties of sediments (grain density, porosity, and composition) occur at many spatial scales in all types of sediments. Sediment bulk properties determine elasticity and density and, therefore, the degree of acoustic response. Variations in properties and processes limit the potential of using acoustic response to differentiate sediment types. Small changes in one or more properties can produce a wide variation in the acoustic response, and empirical curve fitting most often serves as models for these relationships. Sedimentary data and acoustic variability at 30 and 50 kHz from three sites in the Mississippi Sound (Lambert et al., 2002) have been further analyzed and compared for the available Shepard sediment classes. Initial observations revealed trends in acoustic variability based on sediment classification. Clustering techniques were used to estimate the central tendency of the sparse set of geoacoustic measurements based on selected combinations of geotechnical parameters. The group-averaged sediment properties (geotechnical, granulometric, and geoacoustical) partially correlate with the acoustic coefficient of variation of the normal-incidence ping-ensemble 50 kHz response. Changes in acoustic fluctuations at 30 and 50 kHz strongly correlate with water content and compositional variations, and are consistent with volume variability and scattering.