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Technical Manual on the Use of Satellite Images in Ecological Studies

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Technical Manual on the Use of Satellite Images in Ecological Studies Ethiopian Environment and Forest Research Institute TECHNICAL MANUAL ON THE USE OF SATELLITE IMAGES IN ECOLOGICAL STUDIES QGIS INTERFACE Prepared by Nesibu Yahya Solomon Mulat Melaku Getachew February 2019 Addis Ababa, Ethiopia Ethiopian Environment and Forest Research Institute TECHNICAL MANUAL ON THE USE OF SATELLITE IMAGES IN ECOLOGICAL STUDIES Nesibu Yahya Solomon Mulat Melaku Getachew February 2019 Addis Ababa, Ethiopia Copyright©2019 EEFRI EEFRI Manual No. 005 ISBN-978-99944-74-29-5 Website: http://www.eefri.org/ Contents Preface............................................................................................................................................. ii How to use this manual .................................................................................................................. iii 1. Brief introduction to GIS and remote sensing ......................................................................... 1 1.1. Definition of GIS and remote sensing .............................................................................. 1 1.2. Principles of remote sensing ............................................................................................ 1 1.3. Characteristics of remote sensing ..................................................................................... 3 1.4. GIS and Remote sensing data and software program ...................................................... 5 2. Introduction to ecological studies using remote sensing ......................................................... 7 2.1. Definitions of ecology and ecological remote sensing..................................................... 7 2.2. Areas of ecological remotes sensing ................................................................................ 8 2.3. Spatial scale in ecological remote sensing ....................................................................... 9 2.4. Techniques in ecological remote sensing ....................................................................... 11 3. Satellite image acquisition and pre-processing ..................................................................... 13 3.1. Satellite image acquisition ............................................................................................. 13 3.2. Satellite image pre-processing ....................................................................................... 17 4. Image interpretation and classification .................................................................................. 34 4.1. Image interpretation ....................................................................................................... 34 4.2. Image classification and accuracy assessment ............................................................... 37 5. Calculating spectral indices and terrain analysis ................................................................... 51 5.1. Calculating spectral indices ............................................................................................ 51 5.2. Terrain analysis using DEM ........................................................................................... 54 6. Summary ................................................................................................................................ 59 7. Acknowledgments ................................................................................................................. 59 8. References ............................................................................................................................. 60 i Preface Remote sensing is an important technology to support ecological studies. In Ethiopia, many ecological studies are undergoing in research and higher learning institutions at a regional and national scale. However, the techniques of remote sensing were underutilized in many ecological types of researches in Ethiopia. We are strongly believed that ecological studies will be improved one-step ahead in Ethiopia, if the techniques of remote sensing are applied. Therefore, we developed this technical manual to create a link between ecology and remote sensing. This manual aims to show the theoretical background and practical techniques on the use of satellite imagery in ecological studies. The manual will have adequate roles for researchers and student in higher learning institutions to fill up their skill gap on the use of satellite image analysis in QGIS environment. In addition, it is also our hope that this manual will support researchers and practitioners to apply the concept and principle of image classification on ecological studies and management. This manual is not intended, primarily, to introduce the basic concepts of remote sensing. Indeed, we started with a brief introduction and background theories of satellite image as a brainstorm. The manual is, mainly, focuses on the utilization of remote sensing data for ecological studies. Moreover, advanced procedures of image classification are included in the manual. Therefore, the manual is more understandable for those who have basic knowledge of remote sensing and the skill of using remote sensing software packages. We hope it will help readers to improve their knowledge and skill on the technique of satellite image acquisition, processing and classification in QGIS software program. ii How to use this manual The first two chapters of this manual describe the theoretical background and ecological remote sensing. The first chapter covers a brief introduction to the science of remote sensing and GIS. The second chapter explains the basic theoretical lesson on the application of remote sensing in ecological studies. Besides the first two chapters, all the remaining chapters of the manual illustrate the systematic and practical exercise that shows image classification and processing using QGIS. During the practical section, it is necessary to install QGIS software and Google Earth to exercise practically. Even if these software programs are free of charge, it is recommended to download from the official websites of the provider to avoid the risk of a computer virus. Practicing the exercises using sample remote sensing data is highly recommended. Thus, we suggest application of the acquired practical knowledge from the manual to solve the actual problems in your specific area of expertise. iii 1. Brief introduction to GIS and remote sensing Understanding the principles and terminologies in remote-sensing data is relevant prior to satellite image manipulation. In this chapter, we introduce the basic terms of remote sensing and GIS. It starts from the simple definition and continues to describe basic principles and concepts of remote sensing and related spatial data. Finally, the chapter deals with software programs of remote sensing and the sources of remote sensing data, particularly satellite imageries. 1.1. Definition of GIS and remote sensing The acronym GIS stands for Geographical Information System. There are plenty of definitions given for GIS and remote sensing. We will use the following well-known definitions of remote sensing and GIS for this manual. According to ESRI, geographic information system (GIS) is a computer-based tool for mapping and analyzing things that exist and events that happen on earth. GIS technology integrates common database operations such as query and statistical analysis with the unique visualization and geographic analysis benefits offered by maps. Remote sensing is defined as “a science (and to some extent an art) of acquiring information about the Earth's surface without actually being in contact with it. This is done by sensing and recording reflected or emitted energy and processing, analyzing, and applying that information.” (Jensen, 2007). Our eyes, photo camera, remote control, x-ray machines, satellites are excellent examples of remote sensing device. 1.2. Principles of remote sensing In remote sensing, there are different principles that should be understood before conducting satellite image processing and classification. These principles will be covered in the subsequent sections. 1 Radiation, reflection, absorption and transmission In remote sensing, the incoming energy that arises from the sun and interacts with earth surface is called radiation. When the incoming radiation from the Sun reaches the feature of the Earth, some of the energy at specific wavelengths can be reflected, absorbed and transmitted through the surface material. Absorption is a situation when the incoming radiation (energy) is absorbed into the surface. Transmission happens when the incoming radiation passes through a target or surface. Reflection occurs when the incoming radiation "bounces" off the target and is redirected back. Figure 1: Different patterns of radiation Raster and Vector In GIS, the two primary types of spatial models are vector and raster. Certainly, understanding the difference between the two models is prerequisite in performing of any spatial analysis using GIS. Real-world features are represented by point, line and polygon in a vector model. Vector data is mostly used to represent features, which has a discrete boundary such as a parcel of lands, rivers and town. On the other hand, grids of a pixel in the raster model represent the features in the real world. In this case, each pixel value in a raster data (e.g. satellite image) has at least a red, green and blue value. Similarly, each pixel of the Digital Elevation Model (DEM) represents a specific elevation value. Rather, the raster data
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