Equatorial Plasma Bubble Threat Parameterization to Support GBAS Operations in the Brazilian Region

Abstract

The Brazil ionospheric study project aims to develop a new ground-based augmentation system (GBAS) ionospheric threat model to better reflect Brazil's low-latitude conditions. Data processing from the global navigation satellite system for 123 active ionospheric days identified 1017 anomalous ionospheric gradients caused by nighttime equatorial plasma bubbles (EPBs). A significant number of gradients, including the largest verified gradient of 850.7 mm/km, exceed the upper bound (375-425 mm/km) of the conterminous United States (CONUS) threat model. This paper defines a series of parameters to model the geometry of EPBs. A maximum ionospheric delay drop of 35 m and a transition zone between 20 and 450 km are estimated for EPBs that move roughly eastward and parallel to the geomagnetic equator with speeds between 40 and 250 m/s. These parameters are key to the development of a GBAS ionospheric mitigation and safety case for operational approval in Brazil and other lowlatitude locations.

Assessment and mitigation of equatorial plasma bubble impacts on category I GBAS operations in the Brazilian region

“…This process lays the worst‐case parameters on top of each other and does not consider any probabilistic averaging among threat model parameter combinations. Ionospheric observations from Brazil, like those presented in Yoon et al, demonstrate that EPB characteristics are significantly different from those of ionospheric storms in mid‐latitude regions. Thus, we modified the worst‐case impact scenarios (ie, previous CONUS procedure) based on the characteristics of EPBs analyzed in Yoon et al…”

“…The assessment of the Brazilian GBAS ionospheric spatial gradient was carried out by an international and interagency team composed of experts on the ionosphere and GBAS starting in October 2013 . This study utilized dual‐frequency GNSS data collected on 123 active ionospheric days during the peak of Solar Cycle #24 (April 2011‐March 2014).…”

“…Almost all of these points were discovered in the presence of an equatorial plasma bubble (EPB) with plasma depletion . Unlike the ionospheric storms observed in mid‐latitude regions, this ionospheric phenomenon is known to occur during nighttime and has a band‐like spatial structure elongated in a south‐north direction moving eastward .…”

“…In addition to assessing EPB‐induced gradients, the Brazilian ionospheric study also developed a new threat model of EPB characteristics in Brazil based on the analysis of data collected in that region . As illustrated in Figure , threat model parameters describing the three‐dimensional geometry of EPBs, including gradient, transition zone length, maximum depletion, propagation speed, and tilt angle, were defined and estimated.…”

“…Note that an EPB tilt angle is known to have latitudinal variation (see Kelley et al), and thus the tilt angle defined in the simplified EPB threat model is a local tilt angle as a part of large‐scale structure of the plasma bubble. In addition to those parameters, the occurrence time of the observed gradients was also investigated …”