Adaptive Airborne Ionospheric Gradient Monitoring for Dual-Frequency GBAS

Abstract

This work proposes a new method for detecting ionospheric activity in the context of future dual-frequency Ground Based Augmentation Systems (GBAS). We utilize measurements available to an airborne GBAS user to derive a probability for large anomalous ionospheric gradients currently present between the aircraft and the local GBAS station. For this purpose, two metrics in satellite range domain are introduced for activity detection: the first is based on the total ionospheric delay difference between ground and air and the second one uses a cumulative sum (CUSUM) based monitoring approach of the rate of change of ionospheric delay difference estimates. After introducing the new concept for this ionospheric activity monitoring, we explain the design parameters that influence the sensitivity of the test and how they can be adjusted. Based on a large simulation dataset, we evaluate the detection capability of the new approach and subsequently the potential to reduce the ionospheric protection levels under nominal conditions by ensuring the absence of harmful ionospheric disturbances. Finally, the monitoring is applied to a measurement dataset within an experimental GBAS facility to evaluate the potential to improve monitor performance and thus improve nominal availability in the presence of significant local multipath. Overall, the results indicate the potential to improve system availability, especially in situations where few satellites are available, such as when using a single constellation, while being able to detect ionospheric activity before the onset of harmful errors for an airborne GBAS user on approach.