Validation of Surface Elevation from TanDEM-X Digital Elevation Models of Devon Island Ice Cap, Canadian High Arctic Claire Bernard-Grand’Maison A thesis submitted in partial fulfillment of the requirements for the Master of Science degree in Physical Geography Department of Geography, Environment and Geomatics Faculty of Arts University of Ottawa Supervisors Dr. Luke Copland Dr. David Burgess Thesis Committee Dr. Laurence Gray Dr. Anders Knudby © Claire Bernard-Grand’Maison, Ottawa, Canada, 2019 Table of Contents List of Tables ................................................................................................................................ iv List of Figures ............................................................................................................................... vi Acknowledgements ...................................................................................................................... xi Legend ......................................................................................................................................... xiii Abstract ....................................................................................................................................... xiv Chapter 1: Introduction ............................................................................................................... 1 1.1 Thesis Objectives ................................................................................................................................... 4 1.2 Thesis Format ......................................................................................................................................... 4 Chapter 2: Background ................................................................................................................ 6 2.1 Synthetic Aperture Radar and Interferometry ............................................................................... 6 2.2 Scattering Mechanisms in Snow and Ice ........................................................................................ 8 2.2.1 General Backscatter Patterns in Glacier Facies ............................................................. 9 2.3 Occurrence of an Elevation Bias in InSAR Surface Elevations on Glacierized Terrain and Relationship to Interferometric Coherence ......................................................................... 11 2.4 Previous Quantitative Assessments of Elevation Bias in TanDEM-X and Other InSAR DEMs in the Context of Glaciological Applications ............................................................... 13 2.5 TanDEM-X Validation Site: Devon Ice Cap ............................................................................... 16 2.5.1 Ice Cap Geometry .......................................................................................................... 16 2.5.2 Ablation and Accumulation Patterns: Influence of Regional Climate .......................... 18 2.5.3 Mass Balance: Glaciological Time Series and Other Estimates ................................... 24 Chapter 3: Datasets and Methodology ...................................................................................... 31 3.1 TanDEM-X DEMs and Auxiliary Data ........................................................................................ 31 3.1.1 Height Accuracy and Block Adjustment Procedure ...................................................... 32 3.1.2 RawDEMs Auxiliary Data ............................................................................................. 33 3.1.3 Data Processing ............................................................................................................ 34 3.2 Validation Elevation Datasets .......................................................................................................... 35 3.2.1 Point Datasets ............................................................................................................... 35 3.2.2 Raster Optically Stereo-Derived Digital Elevation Models: ArcticDEM ..................... 37 3.3 Calculation of Elevation Bias in Raw TanDEM-X DEMs and Associated Errors .......... 38 3.3.1 ArcticDEM Strip DEM Co-registration ........................................................................ 39 3.4 Potential Variability in TanDEM-X Derived Elevation During the Frozen Season ........ 41 3.4.1 Wide ScanSAR TerraSAR-X and TanDEM-X Scenes .................................................... 41 3.4.2 Snowpack Depth: Automatic Weather Station Data ...................................................... 44 3.5 In-Situ Mass Balance Time Series: Proxy for Summer Conditions and Estimation of the Equilibrium Line Altitude................................................................................................................ 45 ii 3.6 Influence of Near Surface Stratigraphy and Density: Comparison with Subsurface Datasets ................................................................................................................................................. 48 3.6.1 Shallow Firn Cores ....................................................................................................... 48 3.6.2 Ground Penetrating Radar Profiles .............................................................................. 48 Chapter 4: Results....................................................................................................................... 60 4.1 Potential Variability in TanDEM-X Derived Elevation During the Frozen Season ........ 60 4.1.1 Backscatter Variability in Wide ScanSAR Scenes ......................................................... 60 4.1.2 Snowpack Depth Variability from Automatic Weather Station Data ............................ 62 4.1.3 Combination with Dynamic Elevation Change Estimates ............................................. 63 4.2 Validation of TanDEM-X RawDEMs on Stable Terrain (Off-Ice Cap) ............................. 65 4.3 Updated In-Situ Mass Balance Time Series ................................................................................ 66 4.4 Validation of TanDEM-X Elevation Bias on Devon Ice Cap ................................................ 67 4.4.1 Influence of SAR Acquisition Parameters on Elevation Bias on Glacierized Terrain .. 68 4.4.2 Spatiotemporal Variability in Elevation Bias ................................................................ 69 4.4.3 Comparison with Observations of Near Surface Stratigraphy and Density .................. 73 Chapter 5: Discussion and Conclusion ..................................................................................... 96 5.1 Potential Variability in TanDEM-X Derived Elevation During the Frozen Season ........ 96 5.1.1 Combination of Snowpack Depth Variability and Vertical Velocity Estimates............. 97 5.1.2 Backscatter Variability in Wide ScanSAR Scenes ......................................................... 98 5.2 Validation of TanDEM-X RawDEMs on Stable Terrain (Off-Ice Cap) ........................... 100 5.3 Validation of TanDEM-X RawDEMs on Devon Ice Cap ..................................................... 101 5.3.1 Influence of SAR Acquisition Parameters on Elevation Bias on Glacierized Terrain and Implication for Modelling .......................................................................................... 101 5.3.2 Detection of Spatiotemporal Patterns of Elevation Bias on Devon Ice Cap ............... 103 5.4 Summary of Presented Factors Affecting Surface Elevation on Devon Ice Cap ............ 107 5.5 Conclusion ........................................................................................................................................... 109 Appendix .................................................................................................................................... 114 References .................................................................................................................................. 117 iii List of Tables Chapter 3: Datasets and Methodology Table 3.1 Details of TanDEM-X rawDEMs and associated metadata used in this study. Underlined and in italics are acquisitions that have been rejected from the analysis. Vertical and horizontal (not shown) displacement from the block adjustment procedure have been applied before the analysis, except for the vertical adjustment of 1512481_2 and 3 and the horizontal adjustment of 4 m for 1106088_1 and 2, corresponding to a 1- pixel shift. ....................................................................................................................... 50 Table 3.2 Description of datasets used for elevation validation, their vertical accuracy, and associated references. Extent and overlap of these datasets is shown in Figure 3.3. ..... 51 Table 3.3 Accuracy assessment of the SEARCH laser altimetry point dataset on Devon Ice Cap based on analysis of cross-over points and stable terrain analysis with rawDEM 07/05/2018. ..................................................................................................................... 52 Table 3.4 Summary of applied shifts and co-registration statistics for ArcticDEM strip DEMs (N = 17). .......................................................................................................................... 53 Table 3.5 Specifications of the TerraSAR-X/TanDEM-X Wide ScanSAR (6 beams) scenes used in this study. All scenes are right looking, descending passes from orbit 113 with incidence angles ranging from 22 to 43° acquired