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Session D6: Navigation Using Environmental Features

Navigation Augmentation for Landing on Vertipads Utilizing Optical Detection of Standard ICAO Circular Markings
Finn Hübner, Robert Haupt, Ulf Bestmann, Peter Hecker, TU Braunschweig
Date/Time: Friday, Sep. 20, 2:58 p.m.

This paper reviews the applicability of a navigation calculation based on circular landing pad detection for the landing of manned vertical take-off and landing (VTOL) aircraft on standard helipads/vertipads. The landing of VTOLs in an urban environment poses multiple challenges and requirements regarding its positioning. Supplementing a GNSS/INS pose by exploiting the feature rich visual environment has been shown to make a substantial contribution towards resilience and integrity of a navigation system. In an approach using only existing markings which are specified in ICAO Annex 14 Vol. II (ICAO, 2020) or PTS-VPT-DSN (EASA, 2022) there is a significant prevalence of circular markings for which a concept for detection and relative pose estimation is studied in this paper. First, the landing pad design for VTOLs and helicopters is characterized. Algorithms for the detection of circular markings are developed and their performance is evaluated. Geometric relations in the projective geometry of oblique elliptical cones are exploited to generate a pose estimate with a remaining one degree of freedom. Solutions to fully determine the position are discussed. Based on simulated approach data and full scale flight test measurement data together with precise reference positions the performance of the solution in terms of availability and accuracy is analyzed. Finally, the potential for supplementing an INS/GNSS navigation solution with respect to the application for the landing of manned VTOLs is evaluated. We are able to show the availability of a detected circular marking for the majority of the final descent while the selected filter criteria lead to low false detection rates. Sub-degree accuracy for orientation and sub-meter accuracy for intrinsic position can be achieved, with constant errors in the range of 40 to 10 cm for height estimation. This solution can be used for integrity checking of a GNSS system or directly in an AHRS/INS calculation by a flight controller for automatic landing. For a full extrinsic solution, the next step is to determine an absolute heading by analyzing the Vertipad identification marking.

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