Sediment types determination using acoustic techniques in the Northeastern Gulf of Mexico

Normal incident acoustic techniques were used to determine values of sediment properties (acoustic impedance, sound speed, bulk density, porosity, shear strength, water content, and mean grain size) and map those (acoustic impedance and grain size) in the northeastern Gulf of Mexico. The acoustic data were acquired using a 11 kHz normal incident echo sounder over approximately 2000 km of track line. A calibration factor for echo strength was determined by the comparison of acoustic data to measured impedance from five core samples (ground truth data). This echo strength calibration was used for the entire data set. Values of sediment properties were calculated from sediment impedance using the regressions compiled from the historical core database. Comparison of ground truth and echo strength to data from 20 additional core locations shows close agreement. Discrepancies are probably due to navigation errors or weak returns in deeper water. In addition, sediment disturbance and frequency dispersion can be considered. Using acoustic derived sediment properties, four sediment provinces of the study area are defined as the following types: sandy/silty clay (impedance, 1.6–2.0 106 kg/m2 s), sand-silt-clay and/or clayey sand (impedance, 2.01–2.40 106 kg/m2 s), silt or fine sand (impedance, 2.41–2.90 106 kg/m2 s), medium/coarse sand (impedance, 2.91–4.0 106 kg/m2 s). The areal distributions of the four types coincide with the previous reports based on sediment sampling. Therefore, the acoustic technique can effectively be used to define and classify sediments and map sediment provinces.