Establishment of a Joint Governmental Differential GPS Service for Marine Use in the Baltic Sea

This paper attempts to establish that there is an operational requirement for a very accurate radio navigation system in Fimrish and Swedish waters. This is done by describing the specific climatic and geographical conditions in Scandinavia that mnkes Differential GPS the only feasible choice for general marine radionavigation use. The idea about DGPS hadattracted the authors for quite some time but put 011 hold until a sufficient number of satellites was available. Only the specific requirement from a numberof majorshipowners. toget a more precise radionavigation system for their new ferries, initiated a more rapid development. The authors from Sweden and Finland are also members of the IALA Radionavigation Committee ch‘arged with the task of producing a World Differential GPS standard. Hence it was decided to do the project as a joint effort, ie. on one hand produce the level of radionavigation service the ferry companies desired and on the other hand perform real life testing to support the efforts of the IALA Radionavigation Committee. Parallel to this development also ship transponder (for ship-to-ship as well as ship-to-shore traffic) and integrated navigation systems developments are pursued, on the icebreaker fleets of respective governments, both based upon the use of DGPS. The task of producing a system with two DGPS-stations and monitoring stations was aw‘arded to Magnavox Ltd. Conventional marine radiobeacons are used as data links. The system design is presented in the paper by Magnavox Ltd. Section 7 predicts the annual availability of the DGPS/ radiobeacon broadcasts as a function of location. It also comments on some signal field and noise field measurements which have been taken during the sum- mer of 1991. However, a full evaluation of DGPS/radiobeacon coverage requires data collected over all the seasons of the year, and will not be available for some time. The system covers the ship routes between the Finnish and Swedish capitals, Helsinki and Stockholm. The calculations regarding anticipated coverage and network planning wnsdone by Prof. PerEnge. Analysis of the Radioheacon Broadcast is presented in the paper. The DGPS-system in Finland became operative 3-16199 1 with onereferencestation,andan identical Swedish station shortly thereafter. Tests ‘are made with varying bit rates and so far without error detection and correction. Preliminary results are presented in the paper. If the system works as anticipated and a worldwide standard is accepted a network a DGPS-station is going to be rapidly extended to cover all Finnish and Swedish ship routes, both at the coast and in the inland system.