Chain inspection at sea

On January 2015 the UdG team performed some experiments at sea for testing the final developments regarding chain inspection. We used a high resolution imaging sonar, which delivers acoustic images at near-video frame rate, in order to detect each of the links and follow the chain. In this way, the system can operate regardless of the visibility conditions and the suspended marine fouling that may arise during cleaning. However working with sonar data introduces several challenges (noisy data, insonification artifacts, narrow field of view, etc.) that had to be addressed. We have tackled the problem in two different configurations: a chain lying on the seafloor and a chain suspended vertically in the water column. For each of these configurations we have provided solutions for chain detection and for chain following using forward-looking sonar and also multibeam data in the vertical case.

Mock-up of the chain lying on the seafloor (left) and hanging vertically (middle and right), in Sant Feliu de Guixols (Girona coast). The water visibility was very reduced pointing out the benefit of using acoustic sensors.

Mock-up of the chain lying on the seafloor (left) and hanging vertically (middle and right), in Sant Feliu de Guixols (Girona coast). The water visibility was very reduced pointing out the benefit of using acoustic sensors.

After successful performance of the chain detection and following algorithms in the water tank, we attempted the same procedures at sea, thus performing a final demonstration one step closer to a real operational environment, and exposing the system to more challenging conditions (larger environment, worse visibility, water currents, etc). Finally, we have also developed a system for forward-looking sonar mapping to perform a first evaluation of the chain state at a high level. This allows seeing an overall view of the spatial layout of the links in the environment as well as provides a map of increased signal-to-noise ratio with respect to the individual frames in which features on the range of few centimeters can be appreciated.

mosaic

Search trajectory and inspection of the horizontal chain at sea. After following several waypoints, Girona 500 AUV found the links of the chain and started the inspection. Left image shows the trajectory of the AUV and right image shows the post processed acoustic mosaic of the same trajectory.

Inspection of the chain in vertical position at sea. The left image shows the point cloud representation of the chain acquired with the acoustic multibeam. The right image shows the post-processed acoustic mosaic of the chain acquired with the forward looking sonar.

Inspection of the chain in vertical position at sea. The left image shows the point cloud representation of the chain acquired with the acoustic multibeam. The right image shows the post-processed acoustic mosaic of the chain acquired with the forward looking sonar.

Watch the horizontal chain inspection:

Watch the vertical chain inspection:




Comments are closed.