[J07-1] Tracking the sea floor in motion I

[J07-1-06] Refining ship navigation with precise point positioning to measure seafloor displacement using repeated sidescan sonar surveys

^○John DeSanto, David Sandwell, David Chadwell (University of California San Diego, San Diego, United States of America)

Accurate seafloor geodetic methods are critical to the study of marine natural hazards such as megathrust earthquakes, landslides, and volcanoes. Digital image correlation of repeated sidescan sonar surveys has been demonstrated as a technique for measuring seafloor displacement that is both economical and capable of obtaining measurements accurate to the meter scale regardless of seafloor depth. However, previous studies have been performed using ship navigation accurate to 0.5-0.7 meters and may drift on the scale of 1 meter per hour; these biases are likely expressed as noise in the displacement measurements. Precise point positioning is a GPS processing technique whereby satellite parameters are solved for using a pre-existing network of stations; these parameters can then be used to quickly and accurately solve for the position of additional GPS receivers. This technique is particularly well suited for processing ship GPS systems in very remote locations that may make differential GPS processing difficult. We perform precise point positioning using the kfPANDA package to improve our knowledge of the ship position during sets of repeated multibeam sonar surveys from two cruises, the May 2016 RR1605 cruise south of Palau and the February 2017 SR1704 cruise offshore San Diego, California. Using the improved navigation, we assess the accuracy of seafloor displacement measurements made from digital image correlation of repeated sidescan surveys for ship speeds of 4-6 knots and sonar frequencies of 12 kHz and 70 kHz.