HydroCrawler – An innovative autonomous surface vehicle for high precision underwater measurements

Unmanned or autonomous surface vehicles (USV's/ ASV's) are an important class of vehicles for hydrological surveys in shallow waters. In contrast to a diving autonomous underwater vehicle (AUV), the surface vehicle always provides an accurate and absolute position via global navigation satellite system (GNSS). Additionally, the operator has a permanent and broadband radio connection to the surface vehicle and its sensors. These advantages make surface vehicles very popular for hydrological or mapping missions in shallow waters. With this publication, we introduce the HydroCrawler USV - an autonomous measurement platform based on a quadropod-like buoyancy structure, optimized for high floating stability and accuracy but nevertheless flexible positioning. The platform is equipped with a high frequency multibeam echosounder, a video camera, a sediment profiler as well as a multi-parameter hydrological probe. For special solutions, more than 100 kg of additional mission specific payload - like a sampler, winch or manipulator - can be attached to the HydroCrawler. The system was developed for high-resolution bottom mapping of lakes and volumetric reconstructions of underwater archeological sites (e.g. pile dwelling settlements). Its control system allows for repetitive automated grid and track missions and - with the RTK-GNSS system - a reconstruction in absolute coordinates to visualize the sedimentation changes on the seafloor and the degradation of archeological remains over time.