Using observations of commercial shipping from horizontal arrays deployed close to a shipping lane to map seabed properties

Abstract

Several horizontal arrays were deployed on the seabed off the coast of Florida, outside Port Everglades. This is a busy site for cruise and container ships, commercial shipping obligated to transmit Automatic Identification System (AIS) information, indicating own latlongs, as well as other parameters of their identity and motion. Acoustic data from these arrays and AIS transmissions were recorded for several days, capturing many passing ships that could then be used as sources at known locations for inversion of seabed properties. One of the arrays had geophones sensing three orthogonal vector components of particle velocity, as well as omni-directional pressure. This area is known to have a distressingly range-dependent seabed, making it difficult to successfully perform matched field processing, for example. We will present our processing of this data, including adaptive beamforming of the geophone data and methods that exploit beam migration patterns (in angle and time difference of arrival) to help isolate multipath arrivals, which are mapped via back-propagating rays to specific grazing angles and locations on the sea floor to provide measurements of bottom loss. The complete set of such observations from ship tracks at multiple frequencies, are incorporated into an inversion for seabed properties.