Seafloor geodesy from repeated sidescan sonar surveys

Abstract

Accurate seafloor geodetic methods are critical to the study of marine natural hazards such as megathrust earthquakes, landslides, and volcanoes. We propose digital image correlation of repeated shipboard sidescan sonar surveys as a measurement of seafloor deformation. We test this method using multibeam surveys collected in two locales: 2500 m deep lightly sedimented seafloor on the flank of a spreading ridge and 4300 m deep heavily sedimented seafloor far from any plate boundary. Correlation of these surveys are able to recover synthetic displacements in the across-track (range) direction accurate to within 1 m and in the along-track (azimuth) direction accurate to within 1–10 m. We attribute these accuracies to the inherent resolution of sidescan data being better in the range dimension than the azimuth dimension. These measurements are primarily limited by the accuracy of the ship navigation. Dual-frequency GPS units are accurate to ∼10 cm, but single-frequency GPS units drift on the order of 1 m/h and are insufficient for geodetic application.