HYDRO 2016 Paper 8A3
Thomas Artz, Annette Scheider, Marc Breitenfeld, Thomas Brüggemann, Volker Schwieger, Harry Wirth
Surveying vessels on German federal waterways are equipped with Global Navigation Satellite System (GNSS) receivers or GNSS-INS (Inertial Navigation Systems) coupled systems respectively to determine their position. By receiving and processing a correction signal which is provided by a network of continuously operating reference stations (CORS), they determine a precise GNSS real time kinematic (GNSS-RTK) solution. Thereby, the data being captured by multibeam echo-sounders can be georeferenced, and a map of the channel bottom can be produced.
One crucial point of the entire workflow is the quality of the vessel positions, i.e., the GNSS-RTK solution, which is highly influenced by the surrounding topography. For instance, bridges, buildings, vegetation or narrow valleys can cause multipath effects, refraction or even a complete loss of signal reception (shadowing). In many cases, it is also not possible to receive the correction signals. Then, no RTK solution can be determined. To mitigate such gaps in the GNSS-RTK trajectory, the Integrated Hydrographic Positioning System (HydrOs) was developed, which consists of hardware components on the vessel as well as of software being able to record and analyse dedicated measurements.
The hardware component represents an adjustable multi-sensor system, which includes one or multiple redundant GNSS receivers and an Inertial Measurement Unit (IMU). In addition, a compass, and a Doppler Velocity Log (DVL) are installed. Furthermore, information about the turning rates and the direction of the rudder propellers, as well as a model of water gauge can be connected to the system. For processing the measurements of the sensors and the model data, a software component has been implemented by using an Extended Kalman Filter and complementary outlier tests.
The investigations presented in this paper lead to an actual installation of a HydrOs prototype on vessel. The position could then be derived with a maximal deviation of less than 1 dm for the height component and less than 2 dm for the horizontal component, although GNSS measurement gaps of up to 60 s occurred.