Investigation of GBAS usability in Brazil

Author(s)

Vinícius Amadeu Stuani Pereira

• Document type: Doctoral Thesis
• Press: Presidente Prudente. 2018-11-23.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências e Tecnologia. Presidente Prudente
• Defense date: 2018-09-13
• Advisor: Paulo de Oliveira Camargo; João Francisco Galera Monico

Abstract

Among the methods of GNSS (Global Navigation Satellite System) positioning used by the aviation in the support of the phases of approach and precise landing of aircraft, stand out the SBAS (Satellite-Based Augmentation System) and the GBAS (Ground-Based Augmentation System). GBAS has the ability to correct most of the errors involved in pseudorange from DGNSS (Differential GNSS), provided that the ionospheric layer exhibits undisturbed behavior in the airport region. However, depending on the flow of solar ionization, geomagnetic activity, sunspot cycle, zenith angle of the sun and geographic location, the ionosphere can suffer severe disturbances, posing a threat to the integrity of the GBAS, since the ionospheric effects may be different at small distances. Thus, investigations of systematic errors due to the ionospheric layer in GBAS have been the subject of studies for some years. In this sense, ionospheric threat models, which seek to determine the maximum existing spatial ionospheric decorrelation between the GBAS station and the aircraft approaching an airport, have been developed or evaluated, especially for the northern hemisphere, more precisely to the US territory, which highlights the CONUS (Conterminous United States) Threat Model. In this area, the ionosphere behavior is more stable compared to that observed in Brazil, located in the equatorial and low latitude ionospheric region, which presents the occurrence of Equatorial Ionization Anomaly (EIA), ionospheric bubbles, ionospheric irregularities, ionospheric scintillation and South Atlantic Magnetic Anomaly (SAMA). The implementation of a GBAS in Brazil, through the Department of Airspace Control (DECEA), aroused the interest of its use with safety. Therefore, the research proposed to investigate the applicability of the CONUS Threat Model to GBAS in the Brazilian territory, using the station-pair method, besides estimating the parameters for the main international airports of Brazil, considering the seasonal variation, as well as investigating the benefits of using the GLONASS (Global’naya Navigatsionnaya Sputnikovaya System), Galileo and GPS (Global Positioning System) L5 carrier in the model. For this purpose, GNSS data from several active networks were used between 2000 and 2016, as well as data from GBAS installed at Rio de Janeiro International Airport (Galeão). For the determination of the parameters of the threat model and the σvig (vertical ionospheric gradient sigma) integrity parameter, the latter used to estimate the aircraft horizontal and vertical protection levels, a system called MoR_Ion was implemented. The parameters of the CONUS model estimated for Brazil, using GPS signals for the combination of L1/L2 carriers, showed that it is impracticable to use a GBAS considering the entire national territory. An alternative was a local and temporal estimate for the airports of interest. The values obtained indicate that the GBAS can probably be used in the international airports of São Paulo/SP (Cumbica), Rio de Janeiro/RJ (Galeão), Brasília/DF (President Juscelino Kubitschek) and Recife/PE (Gilberto Freyre) with some restrictions on the season, time of day and satellite elevation. At the international airport of Porto Alegre/RS (Salgado Filho) it is the only one, among the analyzed ones, in which no restriction to the installation of the GBAS in the place was identified from the data set processed. Results using the GPS and Galileo signals for the L1/L5 combination were better than the L1/L2 combination. Regarding GLONASS, it was found that there is a similarity with the GPS results. The determination of the real time σvig for each available satellite was presented as an interesting alternative, since it transmits to the aircraft the actual ionospheric condition at the time of approach and landing, unlike the current GBAS configuration of transmitting a fixed value of σvig which theoretically covers all possible ionospheric disturbances. Estimates of protection levels for approach in Galeão indicated that there is the possibility of performing a CAT-I procedure, using GPS or GLONASS satellites (L1/L2 combination), provided that previously established local-temporal restrictions are applied. It was also verified that the use of GLONASS satellites in concomitance with GPS allows obtaining values that meet the thresholds for a CAT-III landing, since a larger number of satellites and, consequently, a better geometric configuration, is made available. A case study using the time-step method for the airport region of São José dos Campos/SP, where five stations are located within a 10 km radius, indicated that gradients of this method can be used to estimate the parameter values. However, this method has little resemblance to the architecture of a GBAS station and an aircraft approaching and additionally does not solve the temporal decorrelation. Finally, an alternative method that may indicate whether or not the landing is carried out is to monitor ionospheric irregularities in real time in the surrounding region of a given airport. A real-time experiment using GPS and GLONASS data from March 2014 (near the peak of the solar cycle 24) showed strong irregularities for the Galeão region, with the ionospheric front moving from southwest to northeast. Thus, one way that can be used to estimate protection levels is to not use satellite signals that cross such irregularities. (AU)

• FAPESP's process: 15/20522-7 - ASSESSMENT AND USABILITY OF GBAS IN BRAZIL
• Grantee: Vinícius Amadeu Stuani Pereira
• Support Opportunities: Scholarships in Brazil - Doctorate