Modeling of Barometric Altimeter Measurements to support Geodetic Altitude Navigation

Kurzfassung

Vertical Navigation is of great importance for safe aircraft navigation and guidance, which have been for decades based on standard pressure altitude to support the determination of aircrafts flight levels. This altitude is obtained from airborne pressure measurements performed by barometers and is referenced to the International Standard Aatmosphere Mean Sea Level isobar surface. Standard pressure altitude deviates from true geodetic altitude, that is the one used by GNSS and referenced to an Earth's reference ellipsoid, up to several hundreds of meters for aircrafts flying at typical civil aviation cruise altitudes. Accurate and reliable geodetic altitude navigation is necessary and critical for airport vicinities operations and for new applications like Urban Air Mobility or Alternative Positioning Navigation applications. Although Inertial Navigation Systems and Global Navigation Satellite Systems are able to provide geodetic altitude estimation, both kinds of navigation systems show normally poorer performances in vertical navigation than in the horizontal one. First, this thesis investigates the accuracy in the computation of geodetic altitude from a corrected pressure altitude computed with barometric pressure and external weather data. This computation method is herein shown to remarkably reduce the deviation of the standard pressure altitude from the true geodetic altitude. Secondly, this work derives two robust error models to support the use of barometric pressure measurements for safe geodetic altitude navigation. The first overbounding model is suitable for the use in snapshot (i.e., single-epoch) algorithms. The second dynamic overbounding model is suitable to be included in sequential estimators and in those applications where the time correlation of the pressure measurements must be properly taken into account. The evaluation of the accuracy obtained in computing geodetic altitude from the corrected pressure altitude as well as the analysis of the residual error models is obtained by the use of data gathered during more than 20 flight hours performed with the Dassault Falcon 20-E5 aircraft within a DLR flight tests campaign.