MONITORING REHABILITATION SUCCESS USING REMOTELY SENSED VEGETATION INDICES AT NAVACHAB GOLD MINE, NAMIBIA MARIA ALETTA BELL BSc Agric, BSc Environmental Management, BSc Hons Environmental Monitoring & Modelling Thesis presented in partial fulfilment of the requirements for the degree of Masters of Science in Geography & Environmental Studies in the Faculty of Science at the Stellenbosch University. Supervisors: Prof A van Niekerk Mr PJ Eloff December 2015 Stellenbosch University https://scholar.sun.ac.za ii DECLARATION By submitting this report electronically, I declare that the entirety of the work contained therein is my own, original work, that I am the sole author thereof (save to the extent explicitly otherwise stated), that reproduction and publication thereof by Stellenbosch University will not infringe any third party rights and that I have not previously in its entirety or in part submitted it for obtaining any qualification. Date: Copyright © 2015 Stellenbosch University All rights reserved Stellenbosch University https://scholar.sun.ac.za iii SUMMARY Remote sensing and vegetation indices were evaluated for its usefulness to monitor the success of the rehabilitation programme of the decommissioned tailings storage facility (TSF1) of the Navachab Gold Mine, Karibib, Namibia. The study aimed to objectively illustrate the rehabilitation progression from tailings (baseline) to soil (capping) and vegetation (planted as well as natural). Baseline data sets of 2004 and 2005 were compared with imagery of 2009, 2010 and 2011. All the images were subjected to panchromatic sharpening using the subtractive resolution merge (SRM) method before georegistration. As no recent accurate topographical maps were available of the study area, the May 2010 image was used as a reference image. All other images were georegistered to this image. A number of vegetation indices (VIs) were evaluated. The results showed that the normalised difference vegetation index (NDVI) and the transformed vegetation index (TVI) provided the most promising results. Although the difference vegetation index (DVI) and enhanced vegetation index (EVI) distinguished the vegetation, rock, and soil classes, it was not as successful as the other VIs in classifying the rain water pond. TVI and NDVI were further evaluated for their efficacy in detecting changes. This was done by generating a series of change images and by qualitatively comparing them to false colour images of the same period. Both the NDVI and TVI delivered good results, but it was found that the TVI is more successful when water is present in the images. The research concludes that change analyses based on the TVI is an effective method for monitoring mine rehabilitation programmes. KEYWORDS Remote sensing, mining, rehabilitation, pansharpening, monitoring, change detection, vegetation indices Stellenbosch University https://scholar.sun.ac.za iv OPSOMMING Afstandswaarneming en plantegroei-indekse is ge-evalueer vir die gebruikswaarde daarvan om sukses van die rehabilitasieprogram vir die geslote slykdam of tailings storage facility (TSF1) van die Navachab Goudmyn, Karibib, Namibië vas te stel. Die studie se doelwit was om die progressie in die rehabilitasie van slyk (basislyn) na grond (dekmateriaal) en plantegroei (aangeplant en natuurlik) te illustreer. Basislyndatastelle 2004 en 2005 is vergelyk met 2009, 2010, en 2011 beelde. Al die beelde is panchromaties verskerp deur die subtractive resolution merge (RSM) metode voor georegistrasie uit te voer. Aangesien geen onlangse, akkurate topografiese kaarte van die studiegebied beskikbaar was nie, is die beeld vir Mei 2010 as ‘n verwysingsbeeld gebruik. Al die ander beelde is op die laasgenoemde beeld gegeoregistreer. Die resultate het gewys dat die normalised difference vegetation index (NDVI) en die transformed vegetation index (TVI) die mees belowende resultate lewer. Al het die difference vegetation index (DVI) en enhanced vegetation index (EVI) goed onderskei tussen plantegroeiklasse en grond- en gesteentesklasse was dit nie so suksesvol met die klassifikasie van die reënwaterpoel nie. TVI en NDVI is verder geëvalueer vir effektiwiteit om verandering waar te neem. Dit is gedoen deur ‘n reeks van veranderingsbeelde te skep en dit dan kwalitatief met die valskleur-beelde vir dieselfde tydperk te vergelyk. Beide die NDVI en TVI het goeie resultate gelewer, maar die TVI was meer suksesvol om beelde met water te klassifiseer. Die navorsing lei tot die gevolgtrekking dat veranderingsanalises met die TVI ‘n effektiewe metode vir die monitoring van rehabilitasie programme is. TREFWOORDE Afstandswaarneming, rehabilitasie, panchromatiese verskerping, monitering, veranderingswaarneming, plantegroei-indekse Stellenbosch University https://scholar.sun.ac.za v ACKNOWLEDGEMENTS I sincerely thank the following people and institutions for assisting me in some way or another during the course of doing this research: The administrative staff of the Department of Geography and Environmental Studies, Stellenbosch University, for helping with all registrations and queries - Marianne Cronje and Catherine Liederman deserve special mention; Prof Adriaan van Niekerk and Mr Piet Eloff for technical guidance and encouragement; Jaurez Dorfling, Hanna Mazus and Dillon Panizzolo from Geo Data Design for endless hours spent on the telephone explaining technicalities on the data provided and ERDAS software; INTERGRAPH for kindly supplying a student’s license of ERDAS Imagine software for four years running; Malcolm Sutton and Kobus Reynecke for assisting me with ArcGIS at short notice, and special thanks to Kobus for the crash course in ArcGIS; Dr Pieter de Necker for invaluable assistance editing this document; and My husband, Graham, and our two daughters, Sunél and Marlise, for believing in me and supporting me throughout. Stellenbosch University https://scholar.sun.ac.za vi CONTENTS DECLARATION…………………………………………………………………. ii SUMMARY……………………………………………………………………….iii OPSOMMING…………………………………………………………………… iv ACKNOWLEDGEMENTS……………………………………………………… v CONTENTS……………………………………………………………………… vi TABLES………………………………………………………………………… viii FIGURES…………………………………………………………………………. x ACRONYMS AND ABBREVIATIONS………………………………………. xii CHAPTER 1 INTRODUCTION 1 1.1 REMOTE SENSING TOOLS FOR MINE REHABILITATION ASSESSMENT .. 1 1.1.1 Mine rehabilitation ................................................................................................ 2 1.1.2 Rehabilitation monitoring options using remote sensing .................................. 3 1.2 NAVACHAB GOLD MINE AS A MODEL FOR STUDY ......................................... 6 1.3 RESEARCH PROBLEM ............................................................................................... 9 1.4 AIM AND OBJECTIVES .............................................................................................. 9 1.5 STUDY SITE ................................................................................................................. 10 1.6 RESEARCH METHODOLOGY AND RESEARCH DESIGN ............................... 11 CHAPTER 2 LITERATURE REVIEW 14 2.1 RESOLUTION .............................................................................................................. 14 2.1.1 Spectral resolution ............................................................................................... 14 2.1.2 Radiometric resolution ....................................................................................... 18 2.1.3 Spatial resolution ................................................................................................. 19 2.1.4 Temporal resolution ............................................................................................ 21 2.2 SPECTRAL CHARACTERISTICS OF LAND COVERS ....................................... 21 2.2.1 Water .................................................................................................................... 22 2.2.2 Vegetation characteristics ................................................................................... 23 2.2.3 Rock and soil ........................................................................................................ 24 2.3 SENSORS AND SENSOR CHARACTERISTICS .................................................... 25 2.4 PROCESSING OF SATELLITE IMAGES ............................................................... 27 2.4.1 Image classification ............................................................................................. 27 2.4.2 Image pre-processing .......................................................................................... 31 Stellenbosch University https://scholar.sun.ac.za vii 2.4.3 Pansharpening ..................................................................................................... 34 2.4.4 Accuracy assessment ........................................................................................... 39 2.5 TRUE AND FALSE COLOUR IMAGES .................................................................. 41 2.6 VEGETATION INDICES ............................................................................................ 41 2.6.1 Simple ratio index ................................................................................................ 43 2.6.2 Difference vegetation index ................................................................................ 43 2.6.3 Normalised difference vegetation index ............................................................ 43 2.6.4 Transformed vegetation index ..........................................................................