Fiber laser based towed array 2006
Publish date: 2006-01-01
Report number: FOI-R--2162--SE
Pages: 26
Written in: Swedish
Abstract
For several years fiber laser sensors have been studied at FOI with the aim of developing an easily handed and lightweight towed array sonar having charateristics comparable to that of a conventional system. As a result, an operational fiber laser based sonar was recently demonstrated. The technology is found mature enough to step from research to development. We describe the demonstrated system from a technical perspective with results from the latest field trial undertaken at Bjurshagen, a site south of Stockholm. In addition, two other experimental trials made during the last year are briefly described one of which was made in the new tank laboratory at FOI in Kista and the other at the Djupviken sea trial facility. The developed fiber laser based towed array is also described in terms of its electrical, optical, and mechanical components. The main objective of the Bjurshagen trials was to characterize the flow noise. For tow velocities up to one meter per second the noise level increased at frequencies below 400 Hz. However it has not been possible to establish that the origin of this noise was due to the flow around the array. Hence, the measured level is to be regarded as an upper limit of the flow noise. A clear dependence on the velocity was not observed. In order to demonstrate the general behaviour of the towed system the recorded acoustic data was used to estimate the bearing to a target boat. The estimated direction was in good agreement with the actual relative positions and orientation of the towed array and the target boat.