“What’s New With CRA” Blog: Status of Underwater Investigations | 06/04/2015
By: Chris Ransome
CRA has been developing various capabilities for underwater inspection using the new generation of high resolution sonars. There are two main types of acoustic sonars for this type of work and one laser system. The laser system is very short range and very small field of view but is highly detailed. It is not widely used as yet, especially in inshore areas that have more muddy waters where it seems not to have been tested. CRA is investigating this tool, but its practical application is down the road. Of the acoustic sources, there are fixed (tripod lowered to the bottom or pole mounted from a structure) and those deployed on a pole over the side of a moving vessel.
CRA has used the tripod mounted systems and they do work well for small areas. Because they do not move (except to mechanically scan) their resolution is quite good, but they can only scan a small section at a time and for longer bulkheads for example are almost cost prohibitive. The many individual frames have to be overlapped and co-registered making it very time consuming and difficult to produce a comprehensive image and report. Field time and especially in-house processing time is significant for larger areas.
Vessel mounted systems, specifically the new multi-beam sonars are becoming very cost effective for larger areas and still offering a good resolution. CRA now owns an R2Sonic 2022 multi-beam system, which we will be using primarily for depth soundings, but which offers several abilities (beam steering and concentration and a higher operating frequency), which make it suitable for looking at vertical bulkheads also. Another piece of equipment, called an Echoscope from Coda-Octopus is a different type of multi-beam forming system that promises even more detail, but at a much higher price point. CRA is currently conducting tests with both the R2Sonic and Coda systems with the cooperation of the equipment manufacturers to fully evaluate the results.