BUILDING A 3D REFERENCE MODEL FOR CANAL TUNNEL SURVEYING USING SONAR AND LASER SCANNING

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Integration of TLS and sonar for the modelling of semi-immersed structures

International audienceIn this chapter, we address the topic of 3D reconstruction of semi-immersed structures from laser and sonar data. We take advantage of recent sonar technologies whose static implementation is close to that of terrestrial laser scanners and which also provide 3D point clouds. After introducing the acquisition devices and their implementation on site, we focus on the characteristics of 3D sonar data and their preprocessing. Then we introduce an original method for combining the heterogeneous data (laser and sonar), captured in different environments. The resulting model was used as a reference to evaluate a mobile mapping system developed later on. Finally, we propose a summary of the contributions and some possible improvements

The effect of external flow on the feeding currents of sessile microorganisms

Microscopic sessile suspension feeders live attached to surfaces and, by consuming bacteria-sized prey and by being consumed, they form an important part of aquatic ecosystems. Their environmental impact is mediated by their feeding rate, which depends on a self-generated feeding current. The feeding rate has been hypothesized to be limited by recirculating eddies that cause the organisms to feed from water that is depleted of food particles. However, those results considered organisms in still water, while ambient flow is often present in their natural habitats. We show, using a point-force model, that even very slow ambient flow, with speed several orders of magnitude less than that of the self-generated feeding current, is sufficient to disrupt the eddies around perpendicular suspension feeders, providing a constant supply of food-rich water. However, the feeding rate decreases in external flow at a range of non-perpendicular orientations due to the formation of recirculation structures not seen in still water. We quantify the feeding flow and observe such recirculation experimentally for the suspension feeder Vorticella convallaria in external flows typical of streams and rivers

An Image-Based Inspection System for Canal Tunnel Heritage

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