# The EGNOS Augmentation in Maritime Navigation +
## 1 Introduction  
The Global Navigation Satellite System (GNSS) has a key role in different sectors, from vehicular, marine and air navigation, to \"social\" location-based services, using satellite positioning in non-professional applications such as in tourism or sport [1]. In the maritime sector, GNSS has become the primary way to obtain Position, Navigation, and Timing (PNT) information at sea. Since 1995, with the full operational capability of the Global Positioning System (GPS), the use of GNSS became a revolution in this field. Consequently, the maritime community is going to rapidly adopt new performance standards for shipborne GPS receiver equipment, and the International Maritime Organization (IMO) recognized GPS and GLONASS (GLObal NAvigation Satellite System) as part of the World-Wide Radio Navigation Systems (WWRNS) for ocean water navigation [2]. In 2015 and 2016 Galileo and Beidou also joined the WWRNS [3, 4]. The International Maritime Organization (IMO) is an agency of the United Nations responsible for improving the safety and security of international shipping, as recalled in the Safety of Life at Sea (SOLAS) Convention of 1974 [3]. The SOLAS Convention was updated and amended through Resolutions issued by the IMO Assembly, the IMO Maritime Safety Committee (MSC), and other IMO bodies. In addition, another objective of IMO is to prevent maritime and atmospheric pollution by maritime vessels. Summarizing, all the standards used in the maritime sector for safety, security and environment are set by the IMO [5]. As recently reported by the EMSA (European Maritime Safety Agency) up to 60% of maritime navigation errors are human made; so, the people steering the ships can make mistakes that can have catastrophic consequences [6]. Accurate and reliable navigationsolutions can prevent most of these accidents. In fact, today all cargo ships in the world with a capacity more than 500 GT are equipped with GNSS receivers (transport requirement of the International Convention for the Safety of Life at Sea (SOLAS)). Furthermore, IMO MSC, in 2015 resolution MSC.401 [7], requires the use of at least two independent constellations of GNSS to calculate a reliable estimate of Position Velocity Time (PVT) solution. Regarding the required level of resilience and integrity in the PVT solution, MSC.401 recommends that on-board equipment is able to provide augmentation data to enhance the performance of the PVT solution in terms of accuracy, availability, continuity and integrity [8; 9; 10; 11]. Using GNSS alone in critical maritime operations; e.g., navigating near ports, is not sufficient to carry out these operations safely. To guarantee the required performance of the PVT solution, the augmentation systems are required during these critical operations. Three types of augmentation systems (AS) for GNSS are available: Satellite Based Augmentation Systems (SBAS), Ground Based Augmentation Systems (GBAS) and Aircraft Based Augmentation System (ABAS). SBAS and GBAS provide integrity information and differential corrections by satellite and ground infrastructures, respectively. ABAS is able to obtain integrity information, using only measurements available on-board; Receiver Autonomous Integrity Monitoring (RAIM) is a common ABAS realization, only making use of redundant GNSS measurements. The current study focuses on SBAS. The SBAS systems broadcast supplementary data to GNSS users via Geostationary Earth Orbit (GEO) satellites. SBAS consists of a network of Reference Stations (RS) covering a large area. These RSs collect data from visible GNSS satellites and further relay them to master stations, computing integrity and differential information for each visible GNSS satellite. This information is uploaded, along with the navigation message, to the GEO satellites, which transmit them to users within the coverage area [8]. SBAS is used and implemented worldwide.