High resolution structural inspection offlooded tunnel using BlueView T2250 360°Multibeam Profiling Sonar and Teledyne PDS
OVERVIEW
Acquiring accurate data on the structural integrity of submerged tunnels, as well as shafts and underwater caverns, has long been a challenging and costly problem for water companies, hydroelectric schemes and mine operators alike. While dewatering of tunnels is one option this can cause additional stress which can cause harm to such assets thereby compounding the problem. Dewatering can also be a costly process to undertake and may also lead to loss of productivity in some circumstances. While Remotely Operated Vehicles (ROVs) have been used for some years to gather visual and sonar data inside tunnels, visual (camera) data is often incomplete or inconclusive due to poor visibility caused by turbidity.
The collection of 3D data using sonar technology is often more beneficial as it allows accurate profile data of the tunnel to be acquired. Single beam scanning sonars are typically used to provide line profiles at periodic intervals. To do this the ROV must be held in position while each discrete scan is conducted. Additionally a continuous spiral/corkscrew profile may be obtained if the sonar is continuously moved through the tunnel however coverage is limited and there is a risk that areas of interest may be missed.
Where high resolution multibeam echo sounders have occasionally been used, their size and cost has often been prohibitive as several multibeam heads have to be integrated to give full 360 degree coverage. This in turn means a larger vehicle must be employed often introducing new challenges of its own.
Enter BlueView’s T2250 multibeam profiling sonar, a compact turnkey system specifically designed to produce high density 3D data to centimetric accuracy. Utilizing high frequency, low power acoustic multibeam technology, the system uses 2100 overlapping narrow beams to create a continuous 360° profile which is streamed to Teledyne PDS software at a frequency of over 20Hz creating a dense 3D point cloud from which a truly detailed analysis of the health of a structure can be made. Designed for use on ROVs but with a built in data logger making AUV deployment equally straight forward, the T2250 allows inspection companies to use existing ROV technologies to map tunnels in fine detail without the risks associated with dewatering. One such company, Loxus Technologies of Finland put their new 360 degree multibeam profiler to the test.
