Variations in seafloor depth estimates under different swath-width characteristics of submarine structures in the California Borderlands

Abstract

[author abstract] The California Continental Borderland region off the coast of Southern California is home to many types of geological features on the seafloor (aka. submarine structures) that have resulted from movement along tectonic plate boundaries. Crespi Knoll, a submarine structure in this area, formed as a gentle restraining bend in association with movement along the Palos Verdes master fault. This study used Crespi Knoll as the canvas on which to experiment with the technology aboard the R/V Thomas G. Thompson from 06-07 February 2016. Depth measurements were collected using the Kongsberg EM302, and were used to compare acquisition modes of the multibeam while paring beam spacing (Equiangle, Equidistance) with beam angle (50o, 60o, 70o) in 5-minute intervals at 4 knot survey increments. Multibeam sonar backscatter was post-processed with CARIS HIPS (ver. 9.1) in both 5 meter and 25 meter resolutions, and spatial surface rugosity was calculated in ArcGIS (ver. 10.3.1). Much variation occurred in the depth estimates when comparing a single survey line of unchanging multibeam acquisition settings to one with changing settings. The unchanging acquisition settings consistently produced deeper depth estimates, and the rugosity increased using the 5m resolution surface data as the finer resolution accounted for the small-scale variations of depth at the seafloor.