Habitat Mapping

Wed, 31 Aug 2011 16:14:23 +0200

In July 2008 several experiments were carried out upstream of the Mequinenza dam on the Ebro river in Spain. This was part of a collaboration project with Ecohydros, a Spanish company that offers aquatic ecosystems consulting services. The purpose of the experiments was to produce several geo-referenced photo-mosaics of the bottom. This was to provide visual validation for a sonar-based system being developed by the company to detect zebra mussel colonies.
During the test trials, the Ictineu vehicle together with the USBL system was mounted outboard of a boat and performed small surveys in some areas of interest. The water turbidity forced navigation close to the bottom to ensure sufficient image quality. This made it difficult to control the vehicle and reduced the performance of the DVL measurements (our device is unable to provide reliable velocity estimates under 1m altitude). Moreover, the harsh environment, with big slopes and large rocks, made the autonomous operation of the vehicle impossible. For this reason, the Ictineu was set to ROV mode and operated from the boat with the help of the real time feedback from the imaging sonar, the vehicle cameras and the position estimate from the USBL.
The results of the different dives were irregular. The unreliable DVL data and the multipath affecting the USBL measurements made it difficult to obtain a good position estimate. The quality of the captured images was also irregular. It was necessary to perform manoeuvres to avoid hitting large rocks present on the scenario and as a consequence, the camera suffered abrupt changes in the altitude, sometimes losing sight of the bottom because of the turbid waters. However, despite all the commented issues, it was still possible to generate some photo-mosaics of sufficient quality.

Dam Inspection

Sun, 7 Aug 2011 16:44:46 +0200

Civil engineers of the hydroelectric companies, carry out periodic visual inspections of the state of the concrete. Commonly this is achieved through a careful visualization of a video recorded by a professional diver or a ROV. Our approach to this problem consist on the use of an AUV which follows a pre-programmed path facing the wall while snapping images. A localisation system based on a moored buoy equipped with a DGPS receiver, an USBL transceiver and a MRU is used to georeference the AUV position. Onboard, a navigation system based on a DVL and a MRU-FOG is used for the AUV navigation. After the mission, the set of gathered images together with the localisation data obtained in the buoy are combined and used to setup an image mosaic of the wall of the dam using an image mosaicking system which has been also developed in our lab.

During February 2009 the final experiments about Visual Dam inspection took place in the Pasteral Dam in Girona (Spain). During the experiment the ICTINEU-AUV followed a survey trajectory while keeping a relative pose (heading and distance) with respect to the wall. Using artificial illumination and a forward looking the camera the robot grabbed images along the trajectory. For real time navigation the robot relied exclusively on DVL-FOG navigation while a USBL-DGPS-MRU system mounted on a floating buoy was used for robot tracking as well as for geo-referencing the images through post-processing. Finally a geo-referenced image mosaic of the dam wall was setup.