Aircraft Based GPS Augmentation Using an On-Board RADAR Altimeter for Precision Approach and Landing of Unmanned Aircraft Systems A thesis presented to the faculty of the Russ College of Engineering and Technology of Ohio University In partial fulfillment of the requirements for the degree Master of Science Andrew R. Videmsek May 2020 © 2020 Andrew R. Videmsek. All Rights Reserved. 2 This thesis titled Aircraft Based GPS Augmentation Using an On-Board RADAR Altimeter for Precision Approach and Landing of Unmanned Aircraft Systems by ANDREW R. VIDEMSEK has been approved for the School of Electrical Engineering and Computer Science and the Russ College of Engineering and Technology by Maarten Uijt de Haag Adjunct Professor of Electrical Engineering and Computer Science Mei Wei Dean, Russ College of Engineering and Technology 3 ABSTRACT VIDEMSEK, ANDREW R., M.S., May 2020, Electrical Engineering and Computer Science Aircraft Based GPS Augmentation Using an On-Board RADAR Altimeter for Precision Approach and Landing of Unmanned Aircraft Systems Director of Thesis: Maarten Uijt de Haag With a growing demand for large unmanned aircraft system operations in the national airspace system, a method to safely and automatically land unmanned aircraft at a wide range of airports with varying levels of equipage is still needed. Currently no navigation system is capable of a fully coupled precision approach and landing without the use of ground based navigational aids. To enable widescale adoption and usage of unmanned aircraft systems, an aircraft based augmentation system that provides precision approach and landing service without sacrificing safety is required to land the aircraft at all runways. This thesis proposes an aircraft based GPS augmentation system using an on-board downward facing radar altimeter for precision approach and landing of unmanned aircraft systems. The proposed architecture is initially evaluated using a simulation environment designed to test multiple different GNSS, radar altimeter, and terrain elevation database configurations. Following the offline simulation, a flight test analysis is completed testing the proposed architecture using pre-recorded flight test data at the Ohio University Airport (OH) and Reno-Tahoe International Airport (NV). Furthermore, this thesis provides a sensitivity study on the systematic errors in the augmentation system to better characterize 4 and account for the inherent errors of the architecture’s subsystems. This thesis then discusses modifications to the previously developed terrain database spot algorithm to better account for the characteristics of the selected radar altimeter. Finally, an approach for future certification is proposed followed by recommendations for further research on the topic. 5 DEDICATION To my family, friends, and colleagues 6 ACKNOWLEDGMENTS I would like to give a special thanks to my advisor, Dr. Maarten Uijt de Haag, for his support, advice, and expertise on the research presented in this thesis. Without his encouragement and supervision this thesis would not have been possible. Thank you to my committee members, Dr. Frank van Graas, Dr. Sabrina Ugazio, and Dr. Justin Frantz for their time and assistance in reviewing, critiquing, and improving my thesis. I want to thank the members of General Atomics Aeronautical Systems Inc., including but not limited to Brandon Suarez, Timothy Bleakley, Jose Fuentes, Fabrice Kunzi, and Xavier Redondo, for the assistance they have provided throughout every step of my masters. Additionally, I would like to thank General Atomics Aeronautical Systems Inc. for providing the funding for this research. I thank every member of the Ohio University Avionics Engineering Center. The professors, engineers, students, and staff of the center are some of the brightest people I have ever had the opportunity to work with. Each and every one of them has provided me with invaluable knowledge and guidance. I would not have been able to do it without them. Most of all, I would like to thank my parents, Michael and Margaret Videmsek, for their support and encouragement. They have shaped me into the person I am today, always providing me with guidance in every goal I have pursued. Thank you! 7 TABLE OF CONTENTS Page Abstract ........................................................................................................................... 3 Dedication ....................................................................................................................... 5 Acknowledgments ........................................................................................................... 6 Table of Contents ............................................................................................................ 7 List of Tables................................................................................................................. 10 List of Figures ............................................................................................................... 12 List of Acronyms and Abbreviations.............................................................................. 14 1 Introduction ....................................................................................................... 17 1.1 Thesis Organization ................................................................................ 19 2 Unmanned Aerial Vehicle Background .............................................................. 21 3 Navigation Performance Background ................................................................. 24 3.1 Navigational Performance Parameters .................................................... 24 3.1.1 Accuracy ..................................................................................... 24 3.1.2 Integrity ...................................................................................... 24 3.1.3 Continuity ................................................................................... 27 3.2 Non-Approach Categories ...................................................................... 27 3.3 Approach Categories .............................................................................. 30 3.4 Navigational Requirements for RPA Autoland........................................ 34 4 Navigational Systems Background ..................................................................... 35 4.1 Instrument Landing System (ILS) ........................................................... 35 4.2 Global Navigation Satellite Systems (GNSS) .......................................... 37 4.2.1 GPS Space Segment .................................................................... 37 4.2.2 GPS Control Segment ................................................................. 38 4.2.3 GPS User Segment ...................................................................... 39 4.2.4 GPS Error Sources ...................................................................... 42 4.3 Aircraft Based Augmentation Systems (ABAS) ...................................... 42 4.4 Satellite Based Augmentation System (SBAS) ....................................... 43 4.4.1 Localizer Performance with Vertical Guidance (LPV) with WAAS 44 4.5 Ground Based Augmentation System Landing System (GLS) ................. 45 8 4.6 Radar Altimeter ...................................................................................... 47 5 Terrain Database Background ............................................................................ 51 5.1 World Geodetic System (WGS) 84 and Earth Gravitational Model (EGM) 96 51 5.2 Digital Elevation Models (DEM) ............................................................ 52 5.3 Digital Terrain Elevation Data (DTED) .................................................. 54 5.4 Shuttle Radar Topography Mission (STRM) ........................................... 55 5.5 LiDAR Generated Terrain Elevation Databases ...................................... 57 5.6 Terrain Database Integrity ...................................................................... 57 5.7 Terrain Referenced Navigation (TRN) .................................................... 59 6 RADAR Altimeter Aiding (RALT Aiding) ........................................................ 60 6.1 System Description and Concept of Operation ........................................ 62 6.2 RALT Aiding Method ............................................................................ 66 6.3 Position Computation ............................................................................. 66 6.3.1 Integrity Computation ................................................................. 68 7 Feasibility Study ................................................................................................ 72 7.1 Simulation Method ................................................................................. 72 7.1.1 Selected Error Statistics .............................................................. 73 7.1.2 Accuracy Calculation Algorithm ................................................. 76 7.1.3 Protection Level Calculation Algorithm ...................................... 78 7.2 Feasibility Results .................................................................................. 78 8 Flight Test Analysis ........................................................................................... 89 8.1 Description of Flight Tests...................................................................... 89 8.2 Analysis Method ...................................................................................