Analysis of 2-axis pencil beam sonar microbathymetric measurements of mine burial at the Martha’s Vineyard Coastal Observatory

Abstract

The changing state of warfare has driven the US Navy's area of operations closer to shore into littoral coastal waters. Mine Warfare has been proven as an extremely effective means of battlespace control in these waters. Mines can be inexpensively mass produced and rapidly deployed over large areas. The most common type of mine in use is the bottom placed mine, an object with simple geometry that sits on the seafloor. These mines often exhibit scour induced burial below the seafloor, making detection through traditional mine hunting methods difficult or impossible, while the mines themselves remain lethal. The Office of Naval Research (ONR) has developed a computer model that predicts the extent of mine burial to aid mine hunting and mine clearing operations. Investigations under ONR's Mine Burial Program are presently being conducted to calibrate and validate this model. This thesis uses data from the deployment of an acoustically instrumented model mine near the Martha's Vineyard Coastal Observatory in part of a larger, 16 total object investigation. A 2-axis pencil beam sonar was deployed concurrently with the mine to obtain microbathymetric measurements of the scour pit development and the progression of mine burial. Data correction techniques to correct for beam pattern induced bathymetry errors and a transformed coordinate system are detailed within. An analysis of scour pit dimensions includes scour depth, area, and volume as well as a look into percent burial by depth as a characteristic measurement important for operational mine hunting. The progression of mine burial is related to the wave climate, unsteady flow hydrodynamic forcing, and bed-load transport. The analysis examines the relative roles of these mechanisms in the scour-infill-bury process.