International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 5

Number 2

June 2011

213

1 INTRODUCTION

EPISOL has been operated in two Phases: Phase 1 in

2008 before Athens RIMS installation and Phase 2

in 2010 after its deployment and integration in

EGNOS ground station network. It has been de-

signed and operated in the Aegean Sea to provide

important information about EGNOS performance at

the edge of the system's service area.

Figure 1: Concept of EPISOL project.

More specifically, EPISOL main objective is the

validation of EGNOS relative position accuracy

achieved in the Aegean Sea and, in the sequel, the

demonstration of alternative methods for redistribu-

tion of EGNOS messages in order to overcome

EGNOS SiS coverage limitations. In this frame, re-

sults from both phases concerning system perfor-

mance and conclusions for system improvement and

future applications in the area, have been drawn.

2 EXPERIMENTS DESIGN

As noted, EGNOS performance is mainly related to

the achieved accuracy on the position domain.

Therefore, the project has included a significant

number of trials and collection of a large amount of

data on vessels that sail towards very popular island

destinations of the national cabotage, tactically. All

routes were carefully chosen in reference with the

highly demanding environment of the Aegean Sea

and designed for trials in the open sea, as well as for

trials for canal, coast and port approach navigation.

Additionally, EPISOL analysis presents the achieva-

ble system integrity performance in Greece adapting

EGNOS standards to International Maritime Organi-

sation (IMO) requirements.

EGNOS Performance Improvement in Southern

Latitudes

L. Panagiotopoulou & K. Frangos

Geotopos S.A., Athens, Greece

ABSTRACT: This paper intends to provide results from “EGNOS Performance Improvement in Southern

Latitudes” (EPISOL) project. EPISOL is performed by the Greek company GEOTOPOS S.A. under a con-

tract with the European Space Agency (ESA). EPISOL project aims at analysing, testing and validating the

European SBAS EGNOS (European Geostationary Navigation Overlay Service) performance, by outpointing

advantages and limitations. It has been designed and operated in a very complicated and demanding environ-

ment, the Aegean Sea (Greece, Southern Europe), in which a huge amount of commercial and cruise vessel

routes are scheduled daily. Technically, EPISOL also exploits the possibility of EGNOS data collection

through other means than the direct Signal in Space (SiS), such as SiSNet (Signal in Space through interNet).

Results from this project will form a solid basis towards navigation service improvements and safety en-

hancements for highly demanded maritime applications, providing important information about EGNOS per-

formance at the edge of the system's service area. In this frame, EPISOL includes a significant number of tri-

als and collection of a large amount of data on coasting vessels in the Aegean before and after the operation of

EGNOS Ranging and Integrity Monitoring Station (RIMS) in Athens. As EGNOS data analysis illustrates the

European SBAS performance, arguably well-established GNSS navigation techniques, such as GPS RTK, of-

fer reference trajectories for direct comparisons on the position domain.

214

EPISOL analysis also illustrates the continuity of

EGNOS SiS and the need to complement with other

means of signal transmission. SiSNet combines the

powerful capabilities of SBAS navigation and web

technologies and thus, EGNOS SiS messages are

transmitted via the internet in real time. Figure 1

shows the concept of EPISOL project.

To validate EGNOS performance, the recently es-

tablished Hellenic Positioning System (HEPOS) has

provided GPS RTK reference trajectories with re-

spect to HEPOS network coverage and HEPOS

NTRIP RTCM corrections transmission due to the

local GPRS network coverage limitations.

Map 1: EPISOL trials in the Aegean Sea.

Considering these limitations and in accordance

with the project's demands, Map 1 shows seven

routes to famous Greek islands, that cover a major

part of the Aegean Sea, selected to carry out EPI-

SOL trials.

3 DATA COLLECTION PLATFORM

ARCHITECTURE

EPISOL data collection platform is described in

Figure 2:

Figure 2: System Architecture.

Two individual Septentrio Polarx2e_SBAS

GNSS dual frequency (L1/L2) receivers were in-

stalled on board. The first receiver was logging

SBAS messages transmitted from both PRN 120 and

PRN 126 EGNOS geostationary satellites. PRN 120

broadcasts EGNOS Operational Signal which pro-

vides the fully tested system service and PRN 126

broadcasts EGNOS Test Signal, including the latest

healthy Athens RIMS data in the system's status

configuration. Currently, Athens RIMS is gradually

integrated in the system network and the latest sys-

tem status is continuously tested before its official

broadcast. The second receiver accessed EGNOS

messages exclusively through SiSNet and the SBAS

PVT (Position – Velocity – Time) solution was be-

ing internally calculated by the receiver's software.

In order to avoid lever-arm effects, both receivers

were receiving satellite data from one antenna and

an antenna splitter was splitting the signal to the re-

ceiver antenna ports. Finally, two laptops connected

to a 3G/GPRS modem were offering internet access,

providing HEPOS RTCM corrections for the refer-

ence trajectories and EGNOS messages through

SiSNet server when GPRS network was available.

The data collection period of Phase 1 opened at early

May 2008 and it was closed at mid July 2008, of

Phase 2 opened at May 2010 and it was closed at

mid October 2010 while in each Phase almost 70

hours of GNSS/SBAS measurements at 1 Hz rate

have been recorded.

4 PERFORMANCE ANALYSIS AND

EVALUATION

For the scope of this paper, positioning results using

EGNOS from three different routes are displayed,

considering the criterion of the equal geographical

distribution along the Aegean Sea. Thus, the north-

ernmost Route I, the Route G at the central latitudes

of the Hellenic sea area and the southernmost Route

A are selected. The performance analysis is focused

on different evaluation objectives on the position

domain. The main objective that is common to all

selected routes, is the comparison of the perfor-

mance of the achieved position accuracy for both

EGNOS Operational Signal and EGNOS Test Signal

as transmitted from PRN 120 and PRN 126 respec-

tively. The reference trajectory is the provided

HEPOS RTK PVT solution, as long as the vessel

was sailing within the limits of HEPOS and local

GPRS network coverage. All positioning results

from the selected data sets are compared with IMO

requirements for both accuracy alone and accuracy /

integrity, as well.