Empirical Predictions of Seafloor Properties Based on Remotely Measured Sediment Impedance
NAVAL RESEARCH LAB STENNIS SPACE CENTER MS MARINE GEOACOUSTICS DIV
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Numerous acoustic systems have been developed over the past 25 years for remote classification of the seabed. Many systems use inversions of echo returns to estimate seafloor impedance and then use empirical relationships to predict other seabed properties from values of impedance. New regressions are presented, separately for siliciclastic and carbonate sediments, which allow prediction of sediment grain size, porosity, bulk density, percent sand and gravel, and sound speed ratio and attenuation from values of an index of impedance product of sound speed ratio and bulk density. This index is independent of pore water temperature and salinity and water depth. The regressions are based on nearly 800 cores collected from 67 shallow water sites around the world 12 carbonate and 55 siliciclastic sites. Data are typically restricted to the upper 30 cm of sediment. The regressions based on the nearly 4,500 common data points from core measurements 3,922 for siliciclastic and 621 for carbonate sediments do not vary significantly from the regressions for siliciclastic sediments first presented by Richardson and Briggs 1993 or between carbonate and siliciclastic sediments, suggesting the empirical predictions universally apply to coastal sediments. Sound speed dispersion, sediment disturbance during core collection and measurement, inequalities between sample size acoustic footprint vs. core diameter, spatial variability, and regression error all affect the accuracy of sediment property predictions. 5 tables, 3 figures, 7 refs.
- Physical and Dynamic Oceanography
- Fluid Mechanics