Five-frequency Galileo long-baseline ambiguity resolution with multipath mitigation

© 2018, The Author(s). For long-baseline over several hundreds of kilometers, the ionospheric delays that cannot be fully removed by differencing observations between receivers hampers rapid ambiguity resolution. Compared with forming ionospheric-free linear combination using dual- or triple-frequency observations, estimating ionospheric delays using uncombined observations keeps all the information of the observations and allows extension of the strategy to any number of frequencies. As the number of frequencies has increased for the various GNSSs, it is possible to study long-baseline ambiguity resolution performance using up to five frequencies with uncombined observations. We make use of real Galileo observations on five frequencies with a sampling interval of 1 s. Two long baselines continuously receiving signals from six Galileo satellites during corresponding test time intervals were processed to study the formal and empirical ambiguity success rates in case of full ambiguity resolution (FAR). The multipath effects are mitigated using the measuremen ts of another day when the constellation repeats. Compared to the results using multipath-uncorrected Galileo observations, it is found that the multipath mitigation plays an important role in improving the empirical ambiguity success rates. A high number of frequencies are also found to be helpful to achieve high ambiguity success rate within a short time. Using multipath-uncorrected observations on two, three, four and five frequencies, the mean empirical success rates are found to be about 73, 88, 91, and 95% at 10 s, respectively, while the values are increased to higher than 86, 95, 98, and 99% after mitigating the multipath effects

Global navigation satellite systems performance analysis and augmentation strategies in aviation

In an era of significant air traffic expansion characterized by a rising congestion of the radiofrequency spectrum and a widespread introduction of Unmanned Aircraft Systems (UAS), Global Navigation Satellite Systems (GNSS) are being exposed to a variety of threats including signal interferences, adverse propagation effects and challenging platform-satellite relative dynamics. Thus, there is a need to characterize GNSS signal degradations and assess the effects of interfering sources on the performance of avionics GNSS receivers and augmentation systems used for an increasing number of mission-essential and safety-critical aviation tasks (e.g., experimental flight testing, flight inspection/certification of ground-based radio navigation aids, wide area navigation and precision approach). GNSS signal deteriorations typically occur due to antenna obscuration caused by natural and man-made obstructions present in the environment (e.g., elevated terrain and tall buildings when flying at low altitude) or by the aircraft itself during manoeuvring (e.g., aircraft wings and empennage masking the on-board GNSS antenna), ionospheric scintillation, Doppler shift, multipath, jamming and spurious satellite transmissions. Anyone of these phenomena can result in partial to total loss of tracking and possible tracking errors, depending on the severity of the effect and the receiver characteristics. After designing GNSS performance threats, the various augmentation strategies adopted in the Communication, Navigation, Surveillance/Air Traffic Management and Avionics (CNS + A) context are addressed in detail. GNSS augmentation can take many forms but all strategies share the same fundamental principle of providing supplementary information whose objective is improving the performance and/or trustworthiness of the system. Hence it is of paramount importance to consider the synergies offered by different augmentation strategies including Space Based Augmentation System (SBAS), Ground Based Augmentation System (GBAS), Aircraft Based Augmentation System (ABAS) and Receiver Autonomous Integrity Monitoring (RAIM). Furthermore, by employing multi-GNSS constellations and multi-sensor data fusion techniques, improvements in availability and continuity can be obtained. SBAS is designed to improve GNSS system integrity and accuracy for aircraft navigation and landing, while an alternative approach to GNSS augmentation is to transmit integrity and differential correction messages from ground-based augmentation systems (GBAS). In addition to existing space and ground based augmentation systems, GNSS augmentation may take the form of additional information being provided by other on-board avionics systems, such as in ABAS. As these on-board systems normally operate via separate principles than GNSS, they are not subject to the same sources of error or interference. Using suitable data link and data processing technologies on the ground, a certified ABAS capability could be a core element of a future GNSS Space-Ground-Aircraft Augmentation Network (SGAAN). Although current augmentation systems can provide significant improvement of GNSS navigation performance, a properly designed and flight-certified SGAAN could play a key role in trusted autonomous system and cyber-physical system applications such as UAS Sense-and-Avoid (SAA)

CONTRIBUTION TO THE STUDY OF THE ATMOSPHERIC REFRACTION ON RADIOWAVES USED IN MODERN GEODETIC TECHNIQUES IN LONG DISTANCE MEASUREMENTS

THE THREE MAIN EFFECTS OF THE ATMOSPHERE ON RADIOWAVE PROPAGATION ARE: ATTENUATION, TIME DELAY AND ANGULAR BENDING. THE TIME DELAY CAN BE SEPARATED INTO HYDROSTATIC AND WET DELAY. DEVELOPED HERE ARE MODELS FOR THE ZENTH WET DELAY ESTIMATION AND FOR THE ELEVATION DEPENDENCE OF THE HYDROSTATIC AND WET DELAY AND THE REFRACTION ANGLE. FOR THE DEVELOPMENT OF THESE MODELS (GLOBAL, SITE AND CLIMATE)RADIOSOUND DATA HAVE BEEN USED WHILE IN MODEL APPLICATION ONLY SURFACE METEROLOGICAL DATA ARE NEEDED. A SEPARATE STUDY HAS BEEN DONE FOR THE FIVE AVAILABLE MEDITERRANEAN STATIONS AND DEVELOPED ARE MODEL, (SITE AND CLIMATE) FOR USE ONLY IN THIS AREA.ΟΙ ΤΡΕΙΣ ΚΥΡΙΕΣ ΕΠΙΔΡΑΣΕΙΣ ΤΗΣ ΑΤΜΟΣΦΑΙΡΑΣ ΣΤΗ ΔΙΑΔΟΣΗ ΤΩΝ ΜΙΚΡΟΚΥΜΑΤΩΝ ΕΙΝΑΙ: ΕΞΑΣΘΕΝΗΣΗ, ΧΡΟΝΥΣΤΕΡΗΣΗ ΔΙΑΔΟΣΗΣ ΚΑΙ ΚΑΜΠΥΛΩΣΗ ΤΗΣ ΤΡΟΧΙΑΣ ΤΟΥ ΡΑΔΙΟΚΥΜΑΤΟΣ. ΗΧΡΟΝΥΣΤΕΡΗΣΗ ΔΙΑΔΟΣΗΣ ΧΩΡΙΖΕΤΑΙ ΣΕ ΥΔΡΟΣΤΑΤΙΚΗ ΚΑΙ ΥΓΡΗ. ΑΝΑΠΤΥΣΣΟΝΤΑΙ ΜΟΝΤΕΛΑΓΙΑ ΤΗΝ ΕΚΤΙΜΗΣΗ ΤΗΣ ΖΕΝΙΘΙΑΣ ΥΓΡΗΣ ΥΣΤΕΡΗΣΗΣ ΚΑΙ ΤΗΝ ΕΞΑΡΤΗΣΗ ΑΠΟ ΤΗ ΓΩΝΙΑ ΥΨΟΥΣ ΤΗΣ ΥΔΡΟΣΤΑΤΙΚΗΣ ΚΑΙ ΥΓΡΗΣ ΥΣΤΕΡΗΣΗΣ ΚΑΙ ΤΗΣ ΓΩΝΙΑΣ ΔΙΑΘΛΑΣΗΣ. ΓΙΑ ΤΗΝ ΑΝΑΠΤΥΞΗ ΑΥΤΩΝ ΤΩΝ ΜΟΝΤΕΛΩΝ (ΓΕΝΙΚΩΝ, ΤΟΠΙΚΩΝ, ΚΛΙΜΑΤΙΚΩΝ) ΧΡΗΣΙΜΟΠΟΙΗΘΗΚΑΝ ΜΕΤΕΩΡΟΛΟΓΙΚΑ ΔΕΔΟΜΕΝΑ (ΜΕ ΤΗ ΜΟΡΦΗ ΡΑΔΙΟΒΟΛΙΣΕΩΝ) ΕΝΩ ΣΤΗΝ ΕΦΑΡΜΟΓΗ ΤΟΥΣ ΧΡΕΙΑΖΟΝΤΑΙ ΜΟΝΟ ΜΕΤΕΩΡΟΛΟΓΙΚΕΣ ΠΑΡΑΤΗΡΗΣΕΙΣ ΣΤΗΝ ΕΠΙΦΑΝΕΙΑ ΤΟΥ ΕΔΑΦΟΥΣ. ΛΟΓΩ ΤΗΣ ΙΔΙΑΙΤΕΡΟΤΗΤΑΣ ΤΟΥ ΜΕΣΟΓΕΙΑΚΟΥ ΚΛΙΜΑΤΟΣ ΚΑΙ ΧΩΡΟΥ ΟΙ ΔΙΑΘΕΣΙΜΟΙ ΣΤΑΘΜΟΙ ΑΥΤΗΣ ΤΗΣ ΠΕΡΙΟΧΗΣ (ΠΕΝΤΕ ΤΟΝ ΑΡΙΘΜΟ) ΜΕΛΕΤΗΘΗΚΑΝ ΞΕΧΩΡΙΣΤΑ ΚΑΙ ΑΝΑΠΤΥΧΘΗΚΑΝ ΜΟΝΤΕΛΑ (ΤΟΠΙΚΑ ΚΑΙ ΚΛΙΜΑΤΙΚΑ) ΓΙΑ ΕΦΑΡΜΟΓΗ ΜΟΝΟ Σ'ΑΥΤΗ ΤΗΝ ΠΕΡΙΟΧΗ