Investigations of decorrelation effects on the performance of DGNSS systems in the Baltic Sea

Differential Global Navigation Satellite Systems (DGNSS) are a commonly applied technique for safety critical (Safety-of-Life) navigational operations. Since the nineties an augmentation system following the IALA Beacon DGNSS standard has been employed in the maritime sector. As main components the system comprises a reference station and an integrity monitoring station. With the help of the reference station code based corrections are calculated. Simultaneously the reference station and integrity monitoring station run tests regarding the performance of the system to inform the user within a specified time when the system should not be used for navigation. The gained corrections and integrity information are transmitted in the RTCM format via a medium frequency antenna and can be received by users in the surroundings of almost 300 kilometres. The provided corrections represent one of the two key functions of the DGNSS and allow the user to mitigate errors falsifying the own received pseudoranges. The calculated corrections are generated at the reference station site at a certain time. Due to this fact the longer the distance between the reference station and the user is and the more delayed the corrections are the less they are valid. The IALA has specified the accuracy degradation with 0.4 to 1m for each 100nm. Based on measurement activities in the Baltic Sea the paper discusses the performance of the current maritime DGNSS regarding the spatial and temporal decorrelation effects.