First Results Of A Deep Tow Chirp Sonar Seafloor Imaging System

Abstract

ABSTRACT The latest and most innovative technology has been applied towards the development of a full-ocean depth multi-sensor sonar system using linear swept-FM (Chirp) technology. The seafloor imaging system (SIS- 7000) described herein uses Chirp sidescan sonar to provide high resolution imagery at long range, and Chirp subbottom sonar to provide high resolution profiles in both the near bottom and deeper subbottom. The tow vehicle contains a suite of full-ocean depth instrumentation for measuring various oceanographic parameters and for monitoring vehicle status. Top side systems include a sonar display and data logging system as well as real-time sensor status display and tow vehicle control system. This paper will present an overview of this system, describe its technology and capabilities, and present some initial results. INTRODUCTION In June of 1989, the United States Geological Survey (USGS) identified the need for a deep ocean sea floor mapping tool in order to fulfill its charter to map the Exclusive Economic Zone (EEZ) of the United States and territorial waters. In August of 1989 a group of scientists and engineers began the task of formulating the scientific and technical goals for a deep ocean sidescan sonar and swath bathymetry system. In June of 1991 with the technical specifications completed, a request for proposal was initiated for construction and delivery of the system. The contract was awarded to Datasonics Inc., in February of 1992 and the USGS held field acceptance trials aboard the Research Vessel Oceanus in July and aboard Research Vessel Delaware II in August of 1992. There were several goals in the development of the USGS technical specifications for this next generation of sea floor mapping system. The primary goal was to provide the geological community with medium resolution sea floor images from a deep ocean towed vehicle (intermediate between GLORIA and high frequency systems). The seafloor mapping system was primarily designed as a geological mapping tool, but the design concept included a number of additional features that would allow upgrades to the system at a later date. The basic and most fundamental design criterion called for a quantitative acoustic platform with known and predictable acoustic properties. It is believed that this quantitative approach would provide scientists with the ability to classify bottom sediment physical properties from the backscatter data. System flexibility was also addressed. The USGS required the ability to add additional sensors to the vehicle that would allow a scientist the ability to conduct additional experiments. The subsea electronics were designed such that additional analog, digital or serial sensors can be added in the future. Swath bathymetric capabilities were also designed into the system by including an additional array of sonar transducers. The USGS also required the ability to remotely monitor the tow vehicle status and to diagnose problems while the system was deployed. To meet this requirement additional subsea electronics and firmware were provided to perform real-time monitoring of system parameters.