A High-Resolution Survey AUV
Authors: Northcutt Jay G. , Kleiner Art A. , Chance Thomas S. 
Published: October 2008

Detailed geophysical surveys are required in deep water to avoid potential hazards and to provide for the construction and development of offshore oil leases. Unfortunately, data obtained with existing technology can be expensive and often data accuracy may be questionable. Towing cabled or tethered survey platforms, from a project perspective, can be time consuming and, as a result, costly.

To address this problem, C & C Technologies, Inc. of Lafayette, Louisiana, USA has contracted with Kongsberg Simrad for the construction of a HUGIN 3000 deep-water autonomous underwater vehicle (AUV). This survey platform will be integrated with a variety of sensors including high frequency multibeam swath bathymetry and imagery. Other survey sensors include chirp side scan sonar, chirp subbottom profiler, and magnetometer. Vehicle positioning will be provided by a SSBL (Super Short Base Line) system integrated with Doppler speed log, an inertial navigation system, and for surface operations, DGPS. AUV power will be delivered by aluminum oxygen fuel cells.

This paper will address AUV operations, platform performance, sensor specifications and integration, project milestones, and system economics.

Introduction

As the technology applied to energy exploration and production advances to meet the deepwater challenges beyond the continental shelf, Autonomous Underwater Vehicles (AUVs) will be increasingly employed. AUV technology has just reached a milestone with the first commercial purchase of an AUV for industrial use by C & C Technologies, Inc. of Lafayette, Louisiana.

The deep-towed system, the conventional deepwater mapping tool, suffers from chronic waste and inefficiency. To rectify this problem, Kongsberg Simrad has developed the HUGIN 3000 in conjunction with C & C Technologies. The HUGIN 3000 has evolved from an AUV program amassing more than one hundred missions since 1995. This AUV will be integrated with an "acoustic tether" to monitor data acquisition and optimize system performance.

Deep-Towed Systems

The deep-towed system originated as a mapping tool to accommodate large-scale academic surveying projects comprising multiple traverses of lengthy, straight lines. It was later adapted to similar applications, such as pipeline routes, fiber-optic cable routes, and block hazard surveys. Provided by manufacturers such as Klein Associates, EdgeTech, EDO Corporation, Kongsberg Simrad, and Benthos/Datasonics, the deep-towed system is the true precursor to the survey AUV and remains the standard deepwater survey tool of today. Typical deep-tow instrumentation packages include the side scan sonar and subbottom profiler.

Unfortunately, due to the massive amounts of tow cable required (10,000 meters is not uncommon), deep-towed costs are extremely high. Such cable lengths demand huge handling systems and result in a substantial drag when towed. Survey speeds are therefore limited to 2.0 to 2.5 knots and vessel turns often require 4 to 6 hours to accomplish, which devour a painful portion of a survey budget.

Positioning of deep-towed systems embodies the age-old axiom: accuracy vs. cost. Ranked according to cost (with #1 as the highest), the three primary underwater acoustic positioning alternatives are:Long Base Line (LBL).Two-Vessel Ultra Short Base Line (USBL).Single-Vessel USBL (for less than 1,000 meters of water depth).