Faculty of Science Institute of Earth and Environmental Science Geohazards Research Group ____________________________________________________________________________ OBJECT-BASED IMAGE ANALYSIS FOR DETECTING LANDFORMS DIAGNOSTIC OF NATURAL HAZARDS Dissertation For the Degree of Doctor of Natural Sciences (Dr. rer. nat.) In the Scientific Discipline of Geohazards University of Potsdam Submitted by Karolina KORZENIOWSKA Potsdam, Germany April 2017 Published online at the Institutional Repository of the University of Potsdam: URN urn:nbn:de:kobv:517-opus4-402240 http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-402240 Contents Contents ......................................................................................................................................... I Declaration of Authorship .......................................................................................................... III Acknowledgments ....................................................................................................................... V Abstract ...................................................................................................................................... VII Zusammenfassung ...................................................................................................................... IX Abbreviations .............................................................................................................................. XI List of Figures .......................................................................................................................... XIII List of Tables ............................................................................................................................ XV 1. Introduction ..................................................................................................................... 1 1.1. Motivation .......................................................................................................... 1 1.2. Landforms diagnostic of natural hazards ............................................................ 1 1.3. Remote sensing data and their application for natural hazards .......................... 3 1.4. Object-based image analysis and its application for natural hazards ................. 4 1.5. Morphometric variables for landform detection ................................................. 7 1.6. Research questions ............................................................................................. 9 1.7. Author contributions and structure of the thesis ............................................... 11 2. Gullies, dunes, lava fields, & landslides ........................................................................ 13 2.1. Introduction ...................................................................................................... 13 2.2. Previous work ................................................................................................... 15 2.2.1. Detecting gullies from high-resolution digital topography ............. 15 2.2.2. Concepts of terrain roughness ......................................................... 16 2.3. Research area and data ..................................................................................... 17 2.4. Methods ............................................................................................................ 19 2.5. Results .............................................................................................................. 22 2.5.1. Influence of data resolution and kernel size ................................... 22 2.5.2. Finding the optimal decision boundary........................................... 28 2.5.3. Qualitative and quantitative assessment of classification and the role of threshold uncertainty .................................................................. 29 2.6. Discussion ......................................................................................................... 31 2.7. Conclusions ...................................................................................................... 33 3. Lakes .............................................................................................................................. 35 3.1. Introduction ...................................................................................................... 36 3.2. Previous work ................................................................................................... 37 3.2.1. Thresholding methods ..................................................................... 38 3.2.2. Classification methods .................................................................... 39 3.2.3. Classification methods and monitoring .......................................... 40 3.3. Study area and data ........................................................................................... 40 3.4. Methods ............................................................................................................ 42 I 3.5. Results ............................................................................................................... 47 3.5.1. Accuracy of extracted lakes ............................................................ 47 3.5.2. Sources of errors in the analyses ..................................................... 51 3.5.3. Lake-area changes (1995 – 2015) .......................................... 51 3.5.4. Transferability of OBIA approach .................................................. 53 3.6. Discussion ......................................................................................................... 54 3.7. Conclusions ....................................................................................................... 57 4. Snow avalanches ............................................................................................................ 59 4.1. Introduction ....................................................................................................... 60 4.2. Previous work ................................................................................................... 62 4.3. Study area and data ........................................................................................... 64 4.4. Methods ............................................................................................................ 65 4.4.1. Automatic OBIA snow avalanche classification ............................. 65 4.4.1.1. Classifying vegetation, dark objects, and snow .................... 66 4.4.1.2. Removing small objects that do not represent avalanches .... 67 4.4.1.3. Buffering ............................................................................... 67 4.4.1.4. Neighbourhood analysis ....................................................... 67 4.4.1.5. Adding small gaps inside avalanches ................................... 68 4.4.2. Generating reference data ............................................................... 68 4.5. Results ............................................................................................................... 69 4.5.1. Estimated accuracy ......................................................................... 69 4.5.2. Influence of variables used for classification accuracy ................... 70 4.5.3. Topographic factors favourable for snow avalanches ..................... 70 4.5.4. Density of avalanches ..................................................................... 72 4.5.5. Automatic classification of snow-avalanche zones ......................... 72 4.6. Discussion ......................................................................................................... 74 4.7. Conclusions ....................................................................................................... 76 5. Conclusions .................................................................................................................... 79 Appendix A ................................................................................................................................. 89 Appendix B ................................................................................................................................. 91 Appendix C ............................................................................................................................... 101 Bibliography ............................................................................................................................. 123 II Declaration of Authorship I, Karolina Korzeniowska, declare that this thesis entitled, “Object-based image analysis for detecting landforms diagnostic of natural hazards” and the work presented within it are my own. I confirm that: This work was conducted wholly while in candidature for a research degree at Potsdam University. Where any part of this thesis has previously been submitted for a degree or any other qualification at this University or any other institution, this has been clearly stated. Where I have consulted the published work of others, this is always clearly attributed. Where I have quoted from the work of others, the source is always provided. With the exception of such quotations, this thesis is entirely my own work. I have acknowledged all main sources of help. Where the thesis is based on work conducted by myself jointly with others, I have made clear exactly what was done by others and what I have contributed myself.