EDAS (EGNOS Data Access Service): Differential GNSS Corrections for Land Applications

J. Vázquez, E. Lacarra, M.A. Sánchez, Pedro Gómez

Abstract:	EDAS (EGNOS Data Access Service) is the EGNOS ground-based service (through the Internet), which provides free of charge access to all the data generated and collected by the EGNOS infrastructure. EDAS gathers all the raw data coming from the GPS, GLONASS and EGNOS GEO satellites collected by all the receivers located at the EGNOS stations, which are mainly distributed over Europe and North Africa. Once the data are received, EDAS disseminates them over the Internet in real time and through an FTP archive, resulting in the different services depending on the protocol and on format used, along with the type of information available to users. In addition to the aforementioned data, EDAS is also delivering its own products. Among those EDAS products, this paper will investigate the potential use of EDAS Differential GNSS corrections to support land-based applications such as mapping, transportation and emergency services, with special attention to precision agriculture. EDAS service provision is performed by ESSP, as EGNOS Services Provider, under contract with the European GNSS Agency (GSA), the EGNOS program manager. The European Commission (EC) is the owner of EGNOS system (including EDAS) and has delegated the exploitation of EGNOS to the GSA. ESSP also manages the EGNOS Helpdesk, which provides technical support to users answering any potential question or clarification about EDAS, along with the registration of new EDAS users. Firstly, the paper will introduce the EDAS system and its architecture, presenting the main types of data disseminated through its different services and the online information available to the users. As part of this introduction, special attention will be put on the description of the EDAS Ntrip service, which will be the main enabler for the study to be conducted in the scope of this paper. As already mentioned, EDAS is providing differential corrections to the GPS and GLONASS satellites in RTCM format using the Ntrip protocol, taking the EGNOS stations as reference stations. Using this service, GNSS receivers can improve the accuracy of satellite-based positioning systems up to sub-meter level applying Differential GNSS (DGNSS) techniques. Ntrip is an RTCM standard widely adopted for disseminating differential corrections and GNSS streaming data to stationary or mobile users over the Internet. It supports wireless Internet access through Mobile IP Networks, allowing simultaneous mobile devices or receiver connections to a broadcasting host (caster). In order to provide some valuable elements to assess the EDAS DGNSS corrections ability to support land applications, a performance analysis in terms of accuracy and availability has been done, which shows the achieved performance results for different locations in Europe. The EDAS DGNSS corrections have been applied to the GNSS measurements from public reference stations at selected locations in real-time to obtain statistics depending on the baseline distance between rover and reference station and the location over Europe. The results have been assessed, identifying in which conditions and baseline restrictions the EDAS DGNSS Service could provide an enhanced navigation position with respect to GNSS stand-alone and position errors lower than 1 meter. In addition, focusing on the potential added value of the EDAS DGNSS corrections for precision agriculture, the positioning results from the previous exercise have been post-processed to compute the pass-to-pass accuracy according to ISO 12188-1 (Tractors and machinery for agriculture and forestry - Test procedures for positioning and guidance systems in agriculture - Part1: Dynamic testing of satellite-based positioning devices). The pass-to-pass accuracy is a common indicator of the repeatability of measurements specific to agriculture, which is used for assessing the precision of the guidance equipment. The pass-to-pass corresponds to a short-term dynamic performance determined from off-track errors along straight segment passes occurring within a 15 minute time frame. Considering that, for applications like seeding, planting, spreading and spraying, a pass-to-pass accuracy (15 minutes, 95th percentile) below 20 cm is typically required, the obtained results have been analysed to identify the maximum distance from the EDAS reference stations to still meet this performance level. Finally, based on the baseline restrictions from EGNOS stations driven by the previous performance assessment, estimated coverage maps is provided for at least these performance levels: • Sub-metric EDAS DGNSS accuracy performance: understanding that this performance level could be enough for a variety of applications in the mapping, transportation and emergency services domains. • EDAS DGNSS performance improving GNSS only solution: This could be an alternative to improve the GNSS standalone solution for compatible receivers that do not use EGNOS or for users working in challenging environments (e.g. no GEO visibility). • EDAS DGNSS pass-to-pass accuracy (15 minutes, 95th percentile) below 20 cm: This performance could be sufficient for some precision agriculture applications, such as seeding, planting, spreading and spraying. With regards to the coverage maps, the GPRS/GSM coverage within Europe will be considered to take into account the fact that EDAS Ntrip service requires Internet access. In conclusion, the paper provides an indication of the positioning performance supported by the EDAS DGNSS corrections, including the associated coverage areas under different performance criteria which could be of interest for different land applications in the agriculture, mapping, transportation or emergency services domains.
Published in:	Proceedings of the 29th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2016) September 12 - 16, 2016 Oregon Convention Center Portland, Oregon
Pages:	3550 - 3561
Cite this article:	Vázquez, J., Lacarra, E., Sánchez, M.A., Gómez, Pedro, "EDAS (EGNOS Data Access Service): Differential GNSS Corrections for Land Applications," Proceedings of the 29th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2016), Portland, Oregon, September 2016, pp. 3550-3561. https://doi.org/10.33012/2016.14660
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