Satellite-Based Rainfall Estimation: Evaluation and Characterization (A Case Study Over Omo-Gibe River Basin) A THESIS SUBMITED TO THE SCHOOL OF GRADUATE STUDIES OF ADDIS ABABA UNIVERSITY In partial Fulfillment of the requirements for the Degree of Master of Science in GIS and Remote Sensing BY DEREJE MEKONNEN ASFAW JULY 2007 Satellite-Based Rainfall Estimation: Evaluation and Characterization (A Case Study Over Omo-Gibe River Basin) BY Dereje Mekonnen Asfaw A THESIS SUBMITED TO THE SCHOOL OF GRADUATE STUDIES OF ADDIS ABABA UNIVERSITY M.Sc. In GIS and Remote Sensing Program Department of Earth Science APPROVED BY EXAMINING BOARD: SIGNATURE Balemwal Atnafu (PhD) __________________________ Chairman, Department Graduate Committee K.S.R.Murty (PhD) __________________________ Advisor Dagnachew Legesse (PhD) __________________________ Examiner I KV.Suryabhagavan(Phd) __________________________ Examiner II II Acknowledgement It is a great pleasure for me to express my heart felt indebtedness to all individuals and organizations that helped me in the completion of this paper I am very particularly grateful to my essay Supervisor Dr. K.S. R Murthy for his invaluable support in all aspects of my work through out this paper. I would like to express my gratitude to my employer the National meteorological Agency (NMA) for permitting me to continue this study .Thanks also go to Addis Ababa University for making it possible for me to take up this study. I also want to thank to all those NMA staffs that have contributed through providing me technical advice and study materials.To mention a few: Ato Muluegeta Malede, Ato Kassa Fekadu, Ato Dejena Mola (Head of Bahir Dar Meteorological Branch Office), W/t Yitaktu Tesfatsion, for giving me the important hints and technical support at the very start of this study.Thanks also to Ato Mamuye Belihu and Ato Messfine Kassa who were strongly supported me in preparing this thesis and giving encouraging moral support during my study period. Especial thanks also goes to the staffs of the computer and GIS service of the ministry of water resource , for all the moral and material support you have provided me to make this study a success. Thanks also to my course mates for the friendliness and the group work. I extend my thanks to my mother, brothers and sisters for all the loving and encouraging support. In particular I would like to thank my old brother Ato Befekadu Thilahun for his unlimited support and encouragement during my stay in this study Finally, I am very grateful to extend my thanks to my wife Yebechaye(Yebu), and my sons: Luel(Kon-chhu) and Dagmawi(Tomi), whom are source of my strength throughout the study year and for their immeasurable love and concern shown for me. III Table of Contents Acknowledgement Table of Content…………………………………………………………………………....IV List of Figure………………………………………………………………………………..VII List of Table………………………………………………………………………………..VIII Acronyms…………………………………………………………………………………….X Abstract………………………………………………………...........................................XI CHAPTER ONE……………………………………………………………………………………………1 Introduction…………………………………………………………………………….....1 1.1 Background…………...........................................................................................1 1.2 Problem of the Statements……………………….................................................4 1.3 Objectives of the Research………......................................................................5 1.3.1 General Objectives……………………………………………………………..5 1.3.2 Specific Objectives……………………………………………………………..5 1.4 Limitation and Scope of the Study…………………............................................6 1.5 Benefits and Beneficiaries from Expected Output…………...............................6 1.6 Structure of the Dissertation………………………………………………………...8 CHAPTER TWO…………………………………………………………………………………………9 Review of Literature……………………………………………………………….9 2.1 Theoretical Background………………………………………………………………9 2.1.1 Rainfall and Raingauge…………………………………………………………9 2.1.2 Satellite Remote Sensing……………………………………………………...11 2.1.2.1 Remote Sensing…………………………………………………………....11 2.1.2.2 Satellite…………………………………………........................................12 2.2 Rainfall and Satellite–Based Measurements……………………………............15 2.2.1 Meteorological Satellite–METOSAT……...................................................15 2.2.2 Characteristics of METOSAT Satellite……………………………………….21 IV 2.3 Rainfall Estimation Techniques………………………………............................23 2.3.1 TAMSAT Rainfall Estimation System (TRES)…………….........................27 2.4 Previous Research Works………………………………………………………...28 CHAPTER THREE…………………………………………………………………………………..32 General Description of the Study Area…..................................................32 3.1 Overview……………………………………………………………………………..32 3.2 Location…………….........................................................................................35 3.3 Topography and Drainage…………………………………………………………36 3.4 Climatic Features…………………………………………………………………...38 3.5 Socio-economic and Population Profile……………………..............................39 CHAPTER FOUR………………………………………………………………………42 Materials and Methods……………………………………………………….42 4.1 Data Type and Source…………………………………………………………….42 4.2 Methodology…....................................................................................... …...44 4.2.1 Schematic Flow-Chart………………………………………………………..47 CHAPTER FIVE………………………………………………………………………..49 Data Processing and Analysis………………………………………….49 5.1 Data Processing……………………………..................................................49 5.1.1 Input Dataset Format…………………………………...............................49 5.1.2 Extent of Data Records………………………………...............................50 5.1.3 Homogeneous Rainfall Regions (HRR)……………………………..........51 5.1.3.1 Selection and Delineation......................................................….......51 5.1.4 Processing of Gauge Rainfall Data………………..................................54 5.1.5 Building RFE Image from MetoSat -TIR raw DATA……………………..55 5.1.6 RFE Image and Value Extraction Process……………….......................57 V CHAPTER SIX………………………………………………………………………….65 Results and Discussion………………………………………………65 6.1 Evaluation and Interpretations……………………………………………........65 6.1.1 Performance of Value Extracted from RFE………………………………65 6.1.2 Validation and Accuracy……………………………………………………66 6.1.2.1 Bias indicator…………………………………………………………...66 6.1.2.2 Validation using Correlation and Quartile Deviation……………….70 6.1.2.3 Rainfall Surface Map (filled contour pattern)…………………….....74 6.2 Climatological Characterization of RFE Vs Gauge Values.........................75 6.2.1 Rainfall Regime of Omo-Gibe Basin…………………….........................75 6.2.2 Results from Temporal Characterization.…….......................................77 6.2.2.1 Decadal Pattern and Trend of Rainfall……...................................77 6.2.2.2 Monthly and Seasonal Profile........................................................78 6.2.2.3 Maximum Rainfall Profile…….......................................................79 6.2.2.4 Rainfall Surface Map on Temporal Overview...............................80 6.2.3 Results From Spatial Characterization..................................................82 6.2.3.1 Seasonal Profile of Spatial Pattern of RFE value..........................82 6.2.3.2 Rainfall Surface Map on Spatial Overview.................……............85 6.2 Advantage and Disadvantage of Using Satellite Data for Rainfall Estimations…………………………………….................................87 CHAPTER SEVEN……………………………………………90 Conclusion and Recommendations……………………………...90 7.1 Conclusion……………………………………………………………………90 7.2 Recommendations for Future Studies……………………………………...93 References.......................................................................................................95 ANNEXES.........................................................................................................99 VI List of Figures Figure 2.1 The Electromagnetic Spectrum……………………….......................................11 Figure 2.2 Areas viewed by geostationary meteorological satellites…………….............17 Figure 2.3 Rain Bearing (Cumulonimbus) Cloud Viewed from the Earth’s Surface…….19 Figure 2.4 The life cycle of Cloud :( grey area indicates rainfall).Sketched…..................20 Figure 2.5 Comparison of actual and estimated 5-year average rainfall………..............32 Figure 3.1 OMO-GIBE BASIN (Location of the Study Area)...........................................35 Figure 3.2 Physiographic and Land use System of Omo-gibe Basin..............................36 Figure 3.3 Long Year Mean Annual Rainfall of Omo-Gibe Basin…................................38 Figure 4.1 Schematic Flow Chart: Steps in the Analysis and the General Study............48 Figure 5.1 Homogeneous Rainfall Regions of OMO-Gibe Basin....................................53 Figure 5.2 Map of Geographic Distribution of Stations…………………………………….54 Figure 5.3 Average gauge values against CCD hour at 25 degree square pixel size….56 Figure 5.4 The Raw MetoSat-TIR CCD and Processed RFE Image…………………….58 Figure 5.5 Steps in the Processing of RFE Value Extraction………………………….....59 Figure 5.6 Map of RFE image Average for rainfall 2nd decade of august, 2006.............62 Figure 5.7 Extraction of VERTEX for HRRs (ArcMap: Spat. Analysis Tools)….............63 Figure 5.8 Sample View of Value extracted at ASCll file from RFE image…….............63 Figure 6.1 Bias Indicators for 1st Decade August, 2000/2003/2006…………………..........67 Figure 6.2 Bias Indicators for the Month