GAST-D Monitoring Results from Post-processed Flight Trial Data - Performance Evaluation of DLR's GBAS Testbed

Thomas Dautermann, Michael Felux, Anja Grosch, Boubeker Belabbas

Abstract:	The German Aerospace Center (DLR) implemented an experimental GBAS test bed at Braunschweig-Wolfsburg Research Airport. Its compliancy with respect to accuracy, integrity, and availability requirements of CAT-I precision approach has been demonstrated in several flight trails in 2009. The research ground station consists of three Topcon Net G3 dual frequency GNSS receivers with multipath suppressing choke ring antennas, which deliver correlation results for navigation at a rate of up to 20 Hz. However, in the current stage only the certified L1 range and carrier data is used. The high sampling rate was chosen in order to effectively detect cycle slips in the phase data. Stations are separated by baselines between 740 and 770 meters. Due to its high modularity, the station is fully accessible and can be easily reconfigured for research purposes. Currently, reconfiguration to an enhanced infrastructure is taking place to comply with the more stringent requirements of CAT-III / GAST-D approaches. In preparation for this reconfiguration, we post-processed the data collected during the 30 approaches of the 2009 flight trials (flown with DLR’s VFW614 research aircraft) with respect to the GAST-D parameters and requirements defined in the ICAO draft SARPs and RTCA DO-253C. These requirements include a second smoothing filter and pseudorange correction processing with 30s smoothing time on both, ground and aircraft subsystem as well as a battery of new monitors on the airborne side. These monitors include the dual solution ionospheric monitoring architecture, differential correction magnitude check, bias approach monitor, reference receiver fault monitor and fault detection and exclusion. We show the outputs of these monitors during the flight trials and evaluate their performance with the one expected theoretically. We overbound the output of the DSIGMA monitor in order to obtain inflated parameters sV=0.24 m and sL=0.17 m for the reference receiver fault monitor. We evaluated integrity, availability and continuity performance during the flight trials. For this we used dual frequency carrier phase positioning in a combined forward and reverse solution as a truth reference. At no time misleading information or hazardously misleading information occurred and the service was never interrupted or unavailable during any of the approaches. Position accuracy was below 1,86 m vertically and 0.91 m laterally at all times within the GBAS service area. Moreover, we have optimized the location of ground station antennae to fulfill the ICAO requirement of detecting absolute ionospheric gradients above 300 mm/km with the monitoring architectures under the assumption of a worst case placement of the reference station 5 km away from the threshold as suggested by Khanafseh et al. (2010). The optimized configuration for four receivers is linearly distributed along the runway with a maximum baseline of 220 m and allows an increase of allowable carrier phase noise by 20% and therefore to a standard deviation of 8 mm.
Published in:	Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011) September 20 - 23, 2011 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	2985 - 2992
Cite this article:	Dautermann, Thomas, Felux, Michael, Grosch, Anja, Belabbas, Boubeker, "GAST-D Monitoring Results from Post-processed Flight Trial Data - Performance Evaluation of DLR's GBAS Testbed," Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011), Portland, OR, September 2011, pp. 2985-2992.
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