All posts tagged sonar

NTUA and UdG teams working towards chain following

During the last week of November NTUA and UdG members put their efforts together to push forward the autonomous chain cleaning task of the PANDORA Project. To this end it is required to detect the chain links and follow them accurately.

NTUA and UdG teams working at CIRS for the chain following task

NTUA and UdG teams working at CIRS for the chain following task

UdG team provided a module that performs detections of chain links on the sonar imagery. The chain link detector has been designed to overcome the difficulties of performing object recognition on sonar data (such as the presence of noise, moving shadows or intensity alterations due to viewpoint changes). Taking as input the link detections, NTUA team developed a module that fits a curve through the multiple detections and groups them to obtain a waypoint at the center of each link. The last step that must be performed consists in concurrently follow the identified waypoints while performing new detections. Here, two problems were identified. First, the insonification area of the forward-looking sonar lies always several meters ahead of the vehicle, so the AUV must point on the direction of the last link while keeping its position over the current one. Second, if this two movements are not well coordinated the chain can easily drop off the sonar’s field of view since it is very narrow (30ยบ).

ROS visualization while performing chain following

ROS visualization while performing chain following

These algorithms were tested in the UdG water tank using Girona 500 AUV equipped with the ARIS3000 sonar, over a mock up of a chain of 7 meters. Successful results were obtained in the link detection and path generation stages. For the following algorithm new strategies are under development.

Girona 500 AUV equipped with ARIS sonar over the chain scenario

Girona 500 AUV equipped with ARIS sonar over the chain scenario

Sonar mosaicing of chain scenario

After the first successful tests with the ARIS sonar, the UdG team worked towards reproduction of the chain scenario of PANDORA project. A chain of 13 links and a total length of about 7 meters has been built simulating a real mooring chain.

chain scenario

Reproduction of the chain scenario at UdG’s water tank.

Before the first year review of the project, we conducted some experiments inside the UdG water tank to simulate inspection of the chain by means of sonar.

Girona-500, equipped with ARIS, was manually teleoperated along the chain gathering images at a short range to generate afterwards an acoustic mosaic of high resolution.

The following video summarizes the mosaicing process of the sonar images:

The figure below shows the obtained full chain mosaic:

chain mosaic