High Resolution Optical Satellite Imagery Ian Dowman Karsten Jacobsen Gottfried Konecny Rainer Sandau Published by Whittles Publishing, Dunbeath, Caithness KW6 6EG, Scotland, UK www.whittlespublishing.com Distributed in North America by CRC Press LLC, Taylor and Francis Group, 6000 Broken Sound Parkway NW, Suite 300, Boca Raton, FL 33487, USA © 2012 I. Dowman, K. Jacobsen, G. Konecny and R. Sandau ISBN 978-184995-046-6 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, recording or otherwise without prior permission of the publishers. Th e publisher and authors have used their best eff orts in preparing this book, but assume no responsibility for any injury and/or damage to persons or property from the use or i mplementation of any methods, instructions, ideas or materials contained within this book. All operations should be undertaken in accordance with existing legislation and recognized trade practice. Whilst the information and advice in this book is believed to be true and accurate at the time of going to press, the authors and publisher accept no legal responsibility or liability for errors or omissions that may have been made. Printed by Preface Photogrammetry developed slowly during the fi rst 70 years of the twentieth century, but since 1972, when ERTS – later to become Landsat – was launched, the changes have become rapid. Landsat introduced digital images to a wide audience, and when SPOT-1 – an Earth observation satellite – was launched in 1986, photogrammetry using images from space became a major interest of mapmakers and scientists. With Landsat, remote sensing became a recognised subject, initially concerned with the interpretation and clas- sifi cation of images, but then converging with photogrammetry, so that today the two subjects are fully integrated. Th is is particularly so with high resolution optical images, which compete with aerial imagery for smaller-scale mapping; high resolution data is also used for interpretation, studying the environment and intelligence gathering. Th is book is concerned with the photogrammetric use of high resolution images, although aspects of image processing are also discussed. Th e book aims to bring together information on a range of sensors, including their characteristics and the applications to which they are put. Th e defi nition of “high resolution” is not universally agreed upon and for this reason we start with Advanced Spaceborne Th ermal Emission and Refl ection Radiometer (ASTER) data, with 15 m ground sample distance (GSD). Stereoscopic images are acquired and the data is used photogrammetrically, particularly for digital elevation model (DEM) genera- tion. SPOT images with 10 m GSD are among the most widely used, and established the interest in the use of stereoscopic images from space. Th e current commercial sensors with sub 1 m GSD are dealt with in the most detail because of their current importance. Pho- tographic images are not forgotten, however, although their use today is minimal, and is mainly for monitoring purposes. We aim to present comprehensive information on all of these sensors and put them into context in the current world of geospatial information. Th e objective of the book is to explain the way in which high resolution imagery is obtained – along with the issues which surround its collection and use – to students, people working in map production and scientists working in fi elds other than mapping. A step-by-step approach is employed, beginning with a discussion of the fundamentals of mapping from imagery in Chapter 1. x Preface xi Chapter 2 presents a historical overview of the development of optical sensors in space and covers CORONA and other fi lm cameras. Th ese played an important role in the establishment of the use of image data from space, but the problems of fi lm recovery and the limitations of fi lm in processing images led to their demise once SPOT demonstrated what could be done with push-broom stereo imagery. Chapter 3 deals with the generic aspects of sensor hardware and the systems needed to record and transmit data from space, with an introduction to instrumentation to provide data for direct georeferencing of images from space. Chapters 4 and 5 give details of specifi c sensors, particularly those in widespread use. Chapter 4 covers sensors with a GSD of greater than 1 m and includes SPOT 1–4 and ASTER; these sensors are mostly designed to collect stereoscopic data using two or more telescopes, pointing at fi xed or variable angles. On the other hand, the sensors with a GSD of greater than 1 m, discussed in Chapter 5, are mainly agile sensors which can be pointed in any direction, up to given limits. Th ese two chapters discuss the tech- nical specifi cations and performance of the sensors, based on published studies. Chapter 6 is devoted to with calibration, sensor models and orientation. Th is is a key chapter for users of the data and covers both rigorous models and rational polyno- mial coeffi cients, as well as variations of these methods. Th is chapter ends with a comparison of orientation methods. Chapter 7 deals with product generation; the discussion is fairly generic and includes the principles of image matching and the particular problems of DEM generation from satellite-borne sensors. Issues of resolution and interpretation are discussed, again in the context of satellite data. Finally, Chapter 8 presents a review of future developments, discussing future missions and the issues which face further development. Th e authors gratefully acknowledge support from organisations that have provided infor- mation and material used in preparing this book, in particular SSTL of Guildford (UK), GeoEye and DigitalGlobe. We also thank Keith Whittles for his encouragement to start and fi nish the book and Manos Baltsavias and Armin Gruen for their helpful comments. We hope that this book will help to expand the use of high resolution satellite data by enabling students and professionals to understand the technology involved and to appreciate and wonder at the magnifi cent images and detailed information which can be obtained from hundreds of kilometres above the surface of the Earth. Ian Dowman University College London Karsten Jacobsen IPI, Leibniz University, Hannover Gottfried Konecny IPI, Leibniz University, Hannover Rainer Sandau German Aerospace Center Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .x The Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xii List of Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiv Chapter 1 Satellite Imaging Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 1.2 Defi nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 1.2.1 Resolution and pixel size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2.2 Classifi cation of sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2.3 Accuracy and precision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2.4 Geolocation, georeferencing and geocoding . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2.5 Digital elevation models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2.6 Orthoimages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.2.7 Image products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.3 Outline of principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 1.3.1 Satellite orbits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.3.2 Geometry of a single image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.3.3 Earth eff ects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.3.4 Acquisition of stereoscopic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.3.5 Heights from stereoscopic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1.3.6 Determination of position and orientation . . . . . . . . . . . . . . . . . . . . . . . . . 16 1.3.7 Ground control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 1.3.8 Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1.4 Optical imagery in context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18 1.5 Current systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25 v vi Contents Chapter 2 History of Optical Sensors in Space . . . . . . . . . . . . . . . . . . . . .27 2.1 History of space fl ight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27 2.2 CORONA programme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29 2.3 Soviet Kosmos satellites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30 2.4 NASA’s Apollo programme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30 2.5 Earth observation missions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32 2.6 Planetary missions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34 2.7 Space Shuttle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36 2.7.1 Th e German metric camera and the US large format camera . . . . . . . . . . . 36 2.7.2 MOMS-02 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.8 East German and Russian photographic space technology . . . . . . . . . . . .38 2.9 Development of current high resolution cameras . . . . . . . . . . . . . . . . . . . . .39 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41 Chapter 3 Principles of High Resolution Optical Sensors . . . . . . . . . . . . .43 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43 3.2 Topographic mapping concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45 3.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.2.2 Across-track stereo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.2.3 Along-track stereo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 3.3 Important parameters for spaceborne mapping systems . . . . . . . . . . . . . .48 3.3.1 Spatial resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 3.3.2 Radiometric aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 3.3.3 Pointing accuracy and stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 3.3.4 Agility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 3.4 Sensor optics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57 3.5 Focal plane module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60 3.5.1 Mechanical function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 3.5.2 Th ermal function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 3.5.3 Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 3.6 Data recording and transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63 3.6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 3.6.2 Sensor data rates and volumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 3.6.3 Data transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 3.6.4 Possible ways of reducing data volume and downlink rates . . . . . . . . . . . . . 66 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72 Chapter 4 Sensors with a GSD of greater than 1 m up to 16 m. . . . . . . . .75 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75 4.2 General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75 Contents vii 4.3 Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81 4.3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 4.3.2 SPOT range of sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 4.3.3 MOMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 4.3.4 Japanese JERS and ASTER satellites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 4.3.5 ALOS PRISM and AVNIR-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 4.3.6 Indian programme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 4.3.7 Agile satellites in the 1–15 m range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 4.3.8 Small satellites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 4.4 Space photography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103 4.4.1 CORONA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 4.4.2 European and US photography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 4.4.3 Soviet photography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106 Chapter 5 Sensors with a GSD of 1 m or less . . . . . . . . . . . . . . . . . . . . .107 5.1 General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107 5.2 Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .110 5.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 5.2.2 IKONOS-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 5.2.3 QuickBird-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 5.2.4 OrbView-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 5.2.5 EROS B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 5.2.6 KOMPSAT-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 5.2.7 Resurs-DK1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 5.2.8 IRS Cartosat-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 5.2.9 WorldView-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 5.2.10 WorldView-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 5.2.11 GeoEye-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 5.2.12 Announced systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125 Chapter 6 Calibration, Sensor Models and Orientation . . . . . . . . . . . . . .127 6.1 General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127 6.2 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .130 6.2.1 Radiometric calibration and image quality . . . . . . . . . . . . . . . . . . . . . . . . 130 6.2.2 Geometric calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 6.3 Sensor models and orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .139 6.3.1 Images with constant view direction across orbit . . . . . . . . . . . . . . . . . . . 139 6.3.2 Images from agile satellites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 6.4 Approximate orientation methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .152 6.4.1 Terrain-dependent RPC solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 6.4.2 3D affi ne transformation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 6.4.3 Direct linear transformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 viii Contents 6.5 Comparison of orientation methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159 6.5.1 Issues in assessing accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 6.5.2 Results from tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 6.5.3 Accuracy of blocks of images. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .168 Chapter 7 Processing and Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173 7.1 Introduction to matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173 7.2 Preparation of images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174 7.3 Generation of digital elevation models . . . . . . . . . . . . . . . . . . . . . . . . . . . .178 7.3.1 Image matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 7.3.2 Analysis of height models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 7.4 Global digital elevation models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .192 7.4.1 GTOPO30 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .192 7.4.2 Shuttle Radar Topography Mission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 7.4.3 ASTER GDEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 7.4.4 Assessment of ASTER GDEM and SRTM . . . . . . . . . . . . . . . . . . . . . . 193 7.4.5 Other DSMs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 7.4.6 Comparison of global DEMs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 7.5 Orthoimages and orthoimage mosaics . . . . . . . . . . . . . . . . . . . . . . . . . . . .198 7.5.1 Orthoimage geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 7.5.2 Resampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 7.5.3 Image processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 7.5.4 Generating stereo partners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 7.5.5 Mosaicing orthoimages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 7.6 Data fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .206 7.6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 7.6.2 Fusion of digital elevation models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 7.6.3 Image fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 7.7 Mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .211 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .217 Chapter 8 Conclusions and Future Developments . . . . . . . . . . . . . . . . . . . 221 8.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .221 8.1.1 Status of sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 8.1.2 Processing and applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222 8.1.3 Organisational and administrative issues . . . . . . . . . . . . . . . . . . . . . . . . . 222 8.2 Future developments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .223 8.2.1 Future missions and sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 8.2.2 Small satellites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 Contents ix 8.2.3 Coordinated missions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 8.2.4 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 8.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .226 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .227 Satellite Imaging Technology 1 Ian Dowman 1.1 Introduction Imagery acquired from sensors mounted on a satellite has been available to the general public since 1972, when ERTS-1, later to become Landsat-1, was launched. Since then the resolution has steadily increased. Th e fi rst big jump was with SPOT-1 HRV in 1986, which was followed by IKONOS in 1999. Th ese developments have led to the widespread use of satellite data for mapping and the generation of three-dimensional (3D) data. A great deal of information on the methods of using such data and on the results achieved can be found in journals, but this book aims to give a complete over- view of high resolution optical sensors operating from space and the way in which the data can be processed and used. We will present some basic principles and show how they have been applied to current sensors. Th e push-broom imaging system has been used in most sensors launched since SPOT-1 and this has therefore been taken as the common factor. So, for the purpose of this book, “high resolution” is taken to include sensors with a pixel size of less than 16 m. Th is limit is adopted in order to include SPOT and ASTER (Advanced Spaceborne Th ermal Emission and Refl ection Radiometer), which are important sensors for mapping and DEM generation. Classifi cation of sensors is discussed in Section 1.2. Th ese sensors use push-broom technology, can derive images from off -nadir viewing and can be calibrated and used for mapping. Landsat and similar sensors are not covered, as these are not normally rigorously oriented and are mainly used for deriving environmental data. Th is fi rst chapter will give an introduction to SAR and InSAR but will not go into detail. Lidar is not discussed, as its use from space is very limited. 1.2 Defi nitions A number of terms are used throughout the book; the important ones are defi ned and discussed here. Abbreviations and commonly used terms are given in the List of Abbreviations. 1