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Quantifying the Structure of the Woody Element in Savannahs Using Integrated Optical and Synthetic Aperture Radar (SAR) Approach

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Quantifying the Structure of the Woody Element in Savannahs Using Integrated Optical and Synthetic Aperture Radar (SAR) Approach Quantifying the structure of the woody element in Savannahs using integrated optical and Synthetic Aperture Radar (SAR) approach: a stepping stone towards country wide monitoring in South Africa by Laven Naidoo Submitted in partial fulfilment of the requirements for the degree DOCTOR OF PHILOSOPHY (Geoinformatics) in the Faculty of Natural and Agricultural Sciences, University of Pretoria Supervisors: Dr Renaud Mathieu (CSIR & University of Pretoria) Dr Konrad Wessels (CSIR & University of Pretoria) Date: 30 September 2017 1 Table of Contents Table of Contents .................................................................................................................................... 2 List of Figures .......................................................................................................................................... 6 List of Tables ........................................................................................................................................... 9 Dedications ........................................................................................................................................... 11 Acknowledgements ............................................................................................................................... 12 Plagiarism Declaration .......................................................................................................................... 13 List of Publications ................................................................................................................................ 14 List of Acronyms .................................................................................................................................... 15 Thesis Abstract ..................................................................................................................................... 17 Chapter 1: Introduction and literature review .................................................................................... 20 1.1 Savannahs and the importance of its woody component in ecosystem and monitoring processes........................................................................................................................................... 20 1.2 The current status of monitoring the woody component in South Africa ........................... 23 1.3 Woody structural metrics ..................................................................................................... 24 1.3.1 Woody biomass ............................................................................................................. 24 1.3.2 Woody canopy volume ................................................................................................. 25 1.3.3 Woody canopy cover .................................................................................................... 26 1.4 Remote sensing of woody structure ..................................................................................... 26 1.4.1 Passive remote sensing of woody structure ................................................................. 27 1.4.2 Active remote sensing of woody structure ................................................................... 28 1.4.3 Global forest remote sensing products ........................................................................ 31 1.5 Multi-sensor and multi-temporal remote sensing data integration ..................................... 31 1.6 Study aim .................................................................................................................................... 33 1.7 Study objectives and chapter breakdown .................................................................................. 34 1.8 Primary and secondary research questions ................................................................................ 35 Chapter 2 ....................................................................................................................................... 35 Chapter 3 ....................................................................................................................................... 35 Chapter 4 ....................................................................................................................................... 36 Chapter 5 ....................................................................................................................................... 36 2 Chapter 2: Assessment of the Performance of Global Forest Cover Products in South Africa – Establishing the benchmark ................................................................................................................. 38 2.1 Abstract ....................................................................................................................................... 38 2.2 Introduction ................................................................................................................................ 39 2.3 Study Area ................................................................................................................................... 42 2.4 Materials and Methodology ....................................................................................................... 44 2.4.1 Global forest products ......................................................................................................... 45 2.4.2 LiDAR validation datasets..................................................................................................... 45 2.4.3 Global Forest Product Pre-processing ................................................................................. 46 2.4.4 Airborne LiDAR Data Pre-processing ................................................................................... 47 2.4.5 Data extraction process ....................................................................................................... 50 2.4.6 Global Product Accuracy Assessment .................................................................................. 50 2.5 Results ......................................................................................................................................... 53 2.5.1 ALOS PALSAR FNF validation results .................................................................................... 53 2.5.2 Landsat VCF validation results ............................................................................................. 57 2.6 Discussion .................................................................................................................................... 62 2.7 Conclusions ................................................................................................................................. 66 Chapter 3: Savannah woody structure modelling and mapping using multi-frequency (X-, C- and L- band) Synthetic Aperture Radar (SAR) data ........................................................................................ 67 3.1 Abstract ....................................................................................................................................... 67 3.2 Introduction - Background, Aims and Objectives ....................................................................... 68 3.3 Study Area ................................................................................................................................... 72 3.4 Materials and Methodology ....................................................................................................... 74 3.4.1 Remote sensing data ............................................................................................................ 74 3.4.2 Field data .............................................................................................................................. 75 3.4.3 LiDAR data processing, woody structural metrics and validation ....................................... 78 3.4.4 SAR data and processing ...................................................................................................... 80 3.4.5 Data integration, modelling protocols and mapping ........................................................... 82 3.4.6 Error assessment .................................................................................................................. 84 3.5 Results ......................................................................................................................................... 86 3.5.1 Modelling Accuracy Assessment .......................................................................................... 86 3.5.2 Tree Structure Metric and Error Maps ................................................................................. 88 3.6 Discussion .................................................................................................................................... 96 3 3.7 Concluding Remarks .................................................................................................................. 100 Chapter 4: Integration of Optical and L-band Synthetic Aperture Radar (SAR) datasets for the assessment of woody fractional cover in the Greater Kruger National Park region ....................... 102 4.1 Abstract ..................................................................................................................................... 102 4.2 Introduction .............................................................................................................................
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