# The EGNOS Augmentation in Maritime Navigation +
## 2 EGNOS Background
#### EGNOS in Maritime  
The ongoing initiatives for the implementation of EGNOS services for the maritime sector start from the consideration that the corrections may be available from different transmission means, such as EGNOS SiS, or through existing radio beacon stations and Automatic Identification System (AIS). The EGNOS SiS is considered the simplest solution and the most used approach since it is based on the transmission of an EGNOS message by the GEO satellites that can be directly received and applied to the onboard vessel receiver to increase the accuracy and integrity of the navigation solution. The messages are available at 1 Hz and are transmitted at GPS L1 frequency. Corrections from EGNOS GEO satellites are available via the EDAS FTP service. This service is an EGNOS terrestrial data service for authorized users of the service [15]. These corrections are provided in EMS file format for each hour of the day. Each line in the EMS file corresponds to an EGNOS message. The EGNOS correction messages include long- and fast-term corrections. Satellite position and clock corrections are considered long-term corrections, while fast-term corrections are pseudorange corrections. Ionospheric corrections and integrity information are also provided by EMS. Once calculated, these corrections are transmitted as \"differential corrections\" by at least two EGNOS geostationary satellites, covering Europe. Consequently, the service provided by EGNOS SiS fits well with marine applications, so that ships can collect these SBAS corrections from SBAS GEO satellites and apply them to obtain an improved navigation position compared to GPS standalone. In addition, the  
Figure 1: EGNOS architecture [12]. ships could benefit from the integrity provided by EGNOS, which warns users of situations that could affect positioning error. Different studies showed the ability of EGNOS to meet the accuracy and availability requirements for general maritime navigation established in the IMO resolution A.1046 (27) [7]. The performance objectives for maritime applications are generally broken down into ocean, coastal, inland-water, harbour navigation; the IMO Resolution A.1046 (27) requirements for these four generic cases are shown in Table 1[7]. The satisfaction of IMO requirements in maritime is deeply detailed in [8; 18]. In [8], the EGNOS performance was evaluated while considering IMO Resolution A.1046 (27) requirements. The results showed a signal availability of 99.999%, a horizontal accuracy of 0.91 m at the 95 th percentile, and the regions where the IMO requirements on service availability and service continuity are met. The authors concluded that EGNOS was suitable for maritime navigation in coastal and oceanic waters. Also, in [10], a GNSS data collection campaign of 10 days along the Norwegian coast was carried out with the aim of assessing EGNOS performance at user level in the maritime domain at high latitudes in Europe. The performance obtained with the receiver has been compared with the requirements of the IMO Res. A.1046 (27), showing good agreement. In [11], the EGNOS availability and continuity have been evaluated within the area comprised between longitudes 13\({}^{\circ}\) W to 19\({}^{\circ}\) W and latitudes 27\({}^{\circ}\) N to 30\({}^{\circ}\) N with spatial resolution of 0.1\({}^{\circ}\) per 0.1\({}^{\circ}\). The EGNOS Maritime Service met all IMO requirements in the geographic area of latitudes more northern than 28\({}^{\circ}\) N and longitudes more eastern than 16\({}^{\circ}\) W after reaching a Signal Availability of 99.999%, a Service Availability in 99.90% of the predefined rectangular region, and 1.06 m of Horizontal Accuracy at the 95 th percentile. In contrast, the Service Continuity requirement (only required for coastal waters) was met in 62.50% of the predefined region. The authors concluded that the continuity risk was the most limiting factor for expanding the EGNOS Maritime Service in the EGNOS south-west border of coverage. The coverage problem can be also verified in other regions.