Recent Field Demonstrations of the Capabilities of an Underwater Laser Line Scan Imaging System in Environmental Survey and Pipeline Inspection Applications
Authors: Coles Bryan W. 
Published: October 2008

A new, commercially available, tiled-deployable laser line Scan underwater imaging system, the LS-4096, has Recently been demonstrated under a variety of rigorous Operating conditions. The purpose of this paper is to Provide the reader with an appreciation of the current state Of these demonstrations. The paper begins with a brief Discussion of operational results obtained when the LS-4096 was deployed on ART'S XP-21 Autonomous Underwater Vehicle during recent tiled trials in San Diego. A more extensive description of a field trial in the northern North Sea, which was a cooperative effort between Applied Remote Technology of San Diego and Sub Sea Survey of Aberdeen, Scotland, is then presented. During the North Sea trials the LS-4096 was installed on the Sub Sea FOCUS ROTV and used to inspect underwater pipelines From an latitude of 8-10 meters and at speeds of 3.5-5.5 Knots. A visual inspection of one 6.5 mile long section of Pipeline was completed in approximately 90 minutes.

INTRODUCTION

The idea of using laser illuminated sensors in the Underwater environment has been an intriguing possibility ver since the first lasers were demonstrated over 30 yearsAgo. Possible architectures for laser illuminated Underwater imaging systems were discussed publicly for The first time at the initial Ocean Optics Conference Sponsored by the SPIE in 1966(1) and several programs to Develop underwater laser systems were initiated and Actively funded during the late 1960's and early 1970's. These initial programs, unfortunately, failed to meet their Technical objectives or the expectations of their sponsors And were subsequently discontinued. Supporting Technologies such as commercial lasers and digital Electronics continued to mature, however, and by the mid- 1980's it became appropriate to reevaluate the practical Reliability and operational potential of underwater laserSystems. Several underwater laser system developments Programs were initiated between 1986 and 1990 and have Been continuously supported with the result that reliable Operational systems are now becoming commercially available.

The purpose of this paper is to discuss one such system, designated the LS-4096, that is the result of the development efforts of Applied Remote Technology, Inc. ART). This system utilizes state-of-the-art technology to Provide a very user-friendly operator interface, user selectable Image resolution of 512, 1024, 2048, or 4096 Pixels across the fixed 70Â° field-of-view, a video signal Dynamic range of 84dB (14-bit), and a demonstrated useful Operating range of up to six optical beam attenuation Lengths. The underwater portion of the system, which is Built around an efficient solid-state laser, has proven itself toBe rugged, reliable, and capable of providing dependable Performance in the most demanding commercial offshore Environments.

SYSTEM DESCRIPTION

In its most basic form, the LS-4096 consists of the Underwater Optical Sensor, the topside Control Console, and the Communication Link that ties them together. A Useful operational system can be assembled by mounting The optical sensor on a deployment platform, such as an AUV or ROW, and adding several supporting components, Such as an umbilical cable and power supplies. The LS-4096 system is shown pictorially in Figure 1.