Towards a reliable bridge collision warning system for inland vessel navigation based on RTK height determination

Inland shipping is an important pillar of the European transport system; however the challenges of inland navigation due to dense traffic, increasing ship dimension, reduced maneuver space and visibility are multifaceted and increasing. About 20 to 30 collisions per year, partially caused by carelessness, demonstrate the necessity of driving assistance systems for inland waterway applications. The project LAESSI (Guiding and assistance systems to improve safety of navigation on inland waterways) is developing efficient navigation assistance functions for inland waterway transport which aim the reduction of risk of collisions by supporting the skipper in its task. Therefore, nautical information like position, height, velocity and heading has to be determined. One focus in this contribution is a bridge collision warning system, which provides a timely alert to the skipper, whenever the vessel, particularly the wheelhouse or radar mast, will not safely pass the bridge. A feasibility study has identified Global Navigation Satellite System (GNSS) technologies as basis for the reliable height determination for such a bridge collision warning system. This approach requires information about the vertical clearance of the bridge superstructure as well as precise height information in the same height reference system at least 300 m before the vessel will pass the bridge. The high accuracy level of less than 10 cm in the vertical position necessitates the Real Time Kinematic (RTK) as suitable GNSS processing method. RTK is a phase-based differential GNSS technique and uses additional observations from permanent reference stations to mitigate or eliminate effects like tropospheric and ionospheric delays or satellite clocks and orbit errors. As bridge collision warning system is a safely critical application, this means that beside the provision of accurate height information also an integrity monitoring for the complete RTK procedure has to be introduced. The shore-based architecture is designed in such a way that correction data, based on a permanent GNSS reference station network, will be checked for their integrity before they are broadcasted (Pre-Broadcast Monitoring) to the processing computer on the vessel. Furthermore, several station dependent effects like signal interferences, signal losses or multipath effects, caused due to obstacles near the inland waterways, impact the GNSS signals, which hamper or falsify the ambiguity fixing and finally the position results. To prevent the provision of faulty results a further integrity monitoring for the shipborne architecture has to be applied. This shipborne integrity monitoring utilizes on the one hand a number of internal statistical parameters from the RTK algorithm like the conventional used fixed ratio value and on the other hand additional information from other sensors or observations. The contribution will present the derived requirements for accuracy, integrity and time to alert for different inland waterway assistance functions. Furthermore an overview about the system architecture and a communication concept based on VHF Data Exchange System (VDES) communication channels will be given. The main focus, however, is an RTK-algorithm which not only estimates position, velocity and heading, but also provides integrity information. This concept considers in a first realization internal statistical parameters from the RTK adjustment, other observations (e.g. Doppler shift) and physical information (e.g. baseline length of two GNSS antennas). A first measurement campaign was done in July 2016 in Koblenz/Germany on the river Moselle. This test area is characterized by three bridges in a relatively short distance of only 300 m which make the provision of reliable and precise RTK position data rather challenging. The preliminary analyses based on three hours GPS and GLONASS observations showed a high rate (> 85%) of evaluated position and height results, which fulfilled the required cm-level accuracies. The first implementation of the internal integrity check could detect and eliminate faulty results. The results have shown that beside a good height performance also fast provision of the heights after the vessel sailed through the bridges is recognizable. This position data between the bridges allows a provision of information to the skipper to check or adjust the wheelhouse or radar mast height before the next bridge will be passed. In the next implementation the rate of turn and acceleration data from an Inertial Measurement Unit (IMU) will be tightly coupled with the raw GNSS observations. Thereby additional information will be available to evaluate the position, height, velocity and heading results and increase the integrity validation. Furthermore it can be expected that the ambiguities after a complete signal interruption can be fixed faster

Galileo orbit determination using combined GNSS and SLR observations

The first two Galileo In-Orbit Validation satellites were launched in October 2011 and started continuous signal transmission on all frequencies in early 2012. Both satellites are equipped with two different types of clocks, namely rubidium clocks and hydrogen masers. Based on two test periods, the quality of the Galileo orbit determination based on Global Navigation Satellite System (GNSS) and Satellite Laser Ranging (SLR) observations is assessed. The estimated satellite clock parameters are used as quality indicator for the orbits: A bump at orbital periods in the Allan deviation indicates systematic errors in the GNSS-only orbit determination. These errors almost vanish if SLR observations are considered in addition. As the internal consistency is degraded by the combination, the offset of the SLR reflector is shifted by +5 cm, resulting in an improved orbit consistency as well as accuracy. Another approach to reduce the systematic errors of the GNSS-only orbit determination employs constraints for the clock estimates with respect to a linear model. In general, one decimeter orbit accuracy could be achieved

Enabling Assistance Functions for Safe Navigation in Inland Waterways

Inland navigation and shipping is an important pillar of the European Transport System. To support the skipper during safety-critical operations, precise Position, Navigation and Time (PNT) data are required. This work discusses the role of PNT information for enabling inland waterways navigation assistance functions, such as bridge collision warning, mooring aiding or automatic guidance. A Real-Time Kinematic (RTK) technique is developed to provide integrity information alongside reliable and cm-level accurate PNT data. Besides, the transmission of Global Navigation Satellite Systems (GNSS) correction data is investigated. Since Global System for Mobile (GSM) does not currently meet the availability and stability communication requirements along inland waterways, using the Automatic Identification System (AIS) for data transmission is explored. The proposed navigation solution and the communication developments were analysed in real time on challenging GNSS signal-degraded scenarios on the authorized inland waterway testbed. Despite the further developments required on the AIS communication infrastructure, it is shown that our system architecture can nearly meet the integrity and accuracy requirements for driver assistance functions on inland waterways

Estimation of satellite antenna phase center offsets for Galileo

Satellite antenna phase center offsets for the GalileoInOrbitValidation(IOV) and FullOperationalCapability (FOC) satellites are estimated by two different analysiscenters based on tracking data of a global GNSS network. The mean x- and y-offsets could be determined with a precision of a few centimeters. However, daily estimates of thex-offsets of the IOV satellites show pronounced systematic effects with a peak-to-peak amplitude of up to 70 cm that depend on the orbit model and the elevation of the Sun above the orbital plane. For the IOV y-offsets, no dependence on the orbit model exists but the scatter strongly depends on the elevation of the Sun above the orbital plane. In general, these systematic effects are significantly smaller for the FOC satellites. The z-offsets of the two analysis centers agree within the 10–15 cm level, and the time series do not show systematic effects. The application of an averaged Galileo satellite antenna model obtained from the two solutions results in a reduction of orbit day boundary discontinuities by up to one third—even if an independent software package is used

Driver assistance functions for safety inland vessel navigation

Inland shipping is an important pillar of the European transport system, however due to dense traffic, reduced visibility and increasing ship dimensions it is very challenging. About 20 to 30 collisions per year, mainly caused by carelessness, lead to damages on waterway infrastructures like bridges, damages on the vessel or even injured people. This fact demonstrates the necessity of driving assistance functions for inland vessels. This contribution will give an overview about the concluded project LAESSI which includes the require-ments for accuracy, integrity and time to alert for the different assistance functions as well as the de-scription of the complete overall system setup like shore-based and board equipment. A main topic in this project was the first realization of the new communication concept based on VHF Data Exchange System (VDES) the next generation of the AIS communication which will also present here. A challenge in this communication concept was the limited data capacity for transmitting all necessary phase and code corrections for every observation in every epoch

Driving Assistance Systems for Inland Vessels based on High Precision DGNSS

Inland shipping is an important pillar of the German transport system; however the challenges of inland navigation due to dense traffic, increasing ship dimension, reduced manoeuvre space and visibility are multifaceted and increasing. About 20 to 30 collisions per year, partially caused by carelessness, demonstrate the necessity of driving assistance systems for inland waterway applications. The project LAESSI (Guiding and assistance systems to improve safety of navigation on inland waterways) aims to develop efficient navigation assistance functions for inland waterway transport. Therefore, nautical information like position, height and heading has to be determined. One main task of the project is the development of a bridge collision warning system, which could provide a timely alert to the skipper, whenever the vessel will not safely pass the bridge. The paper will inform about the derived requirements and will give an overview about the overall system architecture. In addition the paper provides information about a high accuracy positioning system, based on RTK technology. Further a new com-munication concept based on VDES standards will be described. Finally the paper will report about first results gained in demonstration areas at the rivers Moselle and Main

Galileo Orbit and Clock Quality of the IGS Multi-GNSS Experiment

The Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS) aims at the data collection and analysis of all available satellite navigation systems. In particular the new global and regional satellite navigation systems are of interest, i.e., the European Galileo, the Chinese BeiDou, the Japanese QZSS as well as satellite based augmentation systems. This article analyzes the orbit and clock quality of the Galileo products of four MGEX analysis centers for a common time period of 20 weeks. Orbit comparisons of the individual analysis centers have a consistency at the 5–30 cm level. Day boundary discontinuities range from 4 to 28 cm whereas 2-day orbit fit RMS values vary between 1 and 7 cm. The accuracy evaluated by satellite laser ranging residuals is on the one decimeter level with a systematic bias of about −5 cm for all analysis centers. In addition, systematic errors on the decimeter level related to solar radiation pressure mismodeling are present in all orbit products. Due to the correlation of radial orbit errors with the clock parameters, these errors are also visible as a bump in the Allan deviation of the Galileo satellite clocks at the orbital frequency

Towards an Automatic Entering of Inland Waterway Locks

For the development of autonomous inland water shipping two main approaches can be distinguished: a) the more revolutionary way, the development of a fully autonomous vessel from the scratch and ii) the more evolutionary way, the step by step introduction of advanced driver assistant functionalities. The second approach has the advantage, that all subsystems can be introduced and tested in the market at an early stage, while still having the driver on board. The SCIPPPER project (2018-2021) follows this approach and targets the development driver assistant functionality enabling an automatic entering of waterway locks, which is one of the most challenging tasks within inland navigation. Often large vessels have just some decimeters space available to enter the lock chamber. The visibility of the bow of the vessel is limited, the skipper is about 100 m away and often cargo like containers block the direct line of sight. The maneuvers during lock approach and entering of the lock chamber require very high concentration of the skipper and a good knowledge about the ships behavior. Typically all the propulsion and steering units of the vessel, main engine, rudder and bow thruster have to be operated in parallel. One lockage takes about 30 minutes and ships may pass up to 15 locks a day. Thus a skipper may spend a lot of time of his day with this very demanding task. It is the aim of the project SCIPPPER to enhance this situation and disburden the skipper from this demanding task. The aim is to realize an automatic entering and leaving of a lock by a typical inland vessel. To reach this goal several tasks are addressed: -Advanced GNSS processing techniques are used to provide accurate and integrity monitored information about the ships position and heading. GNSS processing will be based on PPP technology (precise point positioning). -The transmission capabilities of the new VDES system will be used to transmit GNSS corrections. In addition also information about the actual state of the lock will be provided to the assistance system on the vessel. -Close range sensors will provide information about relative position of the vessel when approaching and entering the lock cambers. This information will be fused with the GNSS results. -Advanced control algorithms will control work with all propulsion and steering devices of the vessel. -Measurements and the actual state of the vessel and its actuators will be presented to the skipper in a nautical display. -Entering of a lock chamber will be tested in detailed simulations before full scale trials are carried out. The proposed presentation will explain the different tasks in the project and present the designed setup for the overall system