BUILDING EARTH OBSERVATION Building Earth Observation Cameras discusses the science and technology of building an electro-optical imaging system for a space platform from concept to CAMERAS space qualification and in-orbit evaluation. The book provides a broad overview of various Earth imaging systems with specific examples illustrating the design and development issues that impacted the Indian Remote Sensing Satellite (IRS) cameras and is based on the actual experience of the author, who was intimately involved with the development of cameras for the IRS program. GEORGE JOSEPH It equips imaging system project managers, scholars, and researchers with the ability to look deeper into the systems that they are developing and arms application scientists who use satellite imagery with a greater understanding of the technical aspects and terminology used in defining the performance of the image system. The text traces the historical development of imaging systems, reviews the evolution of Earth observation systems from a global perspective, and examines future trends. This interdisciplinary work: • Presents technical issues associated with the design, fabrication, and characterization of the camera • Provides a narrow focus and end-to-end solutions to all components involved in a successful camera-on-Earth observation system • Covers various stages including image formation, optics, opto-mechanics, material choice, design tradeoffs, fabrication, evaluation, and finally qualifying the system for space use Building Earth Observation Cameras provides the tools needed to enable readers to better understand the concepts and challenges involved in building space-based Earth observation systems. 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Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com Dedicated to all my colleagues in SAC and other centers of ISRO who contributed to build world-class Earth observation cameras Contents Preface ...................................................................................................................xiii Author ..................................................................................................................xvii 1. Introduction .......................................................................................................1 1.1 Remote Sensing .......................................................................................2 1.2 Civilian Earth Imaging System .............................................................3 1.3 Indian Earth Observation Program: The Evolution ...........................5 1.4 Earth Observation System: The Paradigm Shift .................................6 2. Image Formation ...............................................................................................9 2.1 Introduction .............................................................................................9 2.2 Electromagnetic Radiation ..................................................................10 2.2.1 Quantum Nature of Electromagnetic Radiation .................11 2.2.2 Thermal Radiation ...................................................................12 2.2.3 Propagation of Electromagnetic Radiation from One Medium to Another .................................................................12 2.2.4 Diffraction .................................................................................13 2.3 Some Useful Terminologies of the Imaging Systems ......................14 2.4 Aberrations ............................................................................................17 2.4.1 Spherical Aberration ................................................................18 2.4.2 Coma ..........................................................................................19 2.4.3 Astigmatism .............................................................................20 2.4.4 Distortion ..................................................................................20 2.4.5 Curvature of the Field .............................................................20 2.4.6 Chromatic Aberration .............................................................20 2.5 Wave Optics ...........................................................................................22 2.6 Image Quality Evaluation ....................................................................25 2.7 Modulation Transfer Function ............................................................27 2.8 Source of Electromagnetic Radiation for Imaging ...........................31 2.9 Radiometric Consideration ..................................................................31 References .........................................................................................................34 3. Imaging Optics ................................................................................................35 3.1 Introduction ...........................................................................................35 3.2 Refractive Optics ...................................................................................36 3.2.1 Telecentric Lenses ....................................................................40 vii viii Contents 3.3 Reflective and Catadioptric Systems ..................................................43 3.3.1 Types of Reflective Telescope Systems ..................................43 3.3.2 Increasing Field of View of Telescopes .................................46 3.3.2.1 Catadioptric System .................................................47 3.3.2.2 All Reflective Wide Field of View Telescope ....................................................................48 3.4 Stray Light Control and Baffling .........................................................52 3.5 Building a Reflective Telescope ...........................................................54 3.5.1 Selection of Mirror Material ...................................................55 3.5.2 Mirror Fabrication ....................................................................58 3.5.2.1 Lightweighting of Mirror ........................................59 3.5.2.2 Optimizing Lightweight Mirror Structure ....................................................................63 3.5.3 Mirror Mounts ..........................................................................64 3.5.3.1 Bipod Mounts............................................................65 3.5.4 Alignment of Mirrors ..............................................................67 References .........................................................................................................71 4. Earth Observation Cameras: An Overview ..............................................75 4.1 Introduction ...........................................................................................75 4.2 Spatial Resolution ..................................................................................76 4.3 Spectral Resolution ...............................................................................82 4.3.1 Interference Filter .....................................................................86 4.4 Radiometric Resolution ........................................................................87 4.4.1 Radiometric Quality ................................................................88 4.5 Temporal Resolution .............................................................................90 4.6 Performance Specification ...................................................................91 4.7 Imaging Modes ......................................................................................92 4.8 On-Orbit Performance Evaluation ......................................................93 References .........................................................................................................98 5. Optomechanical Scanners ..........................................................................101 5.1 Introduction .........................................................................................101 5.2 Principle of Operation ........................................................................101 5.3 Scanning Systems ...............................................................................103 5.3.1 Scan Geometry and Distortion ............................................110 5.4 Collecting Optics .................................................................................112 5.5 Dispersive System and Focal Plane Layout .....................................113 5.6 Detectors ...............................................................................................117 5.6.1 Detector Figure of Merit .......................................................117 5.6.2 Thermal Detector ...................................................................120 5.6.3 Photon Detectors ....................................................................121 5.6.3.1 Photoemissive Detectors .......................................122 5.6.3.2 Photoconductive Detector .....................................123 5.6.3.3 Photovoltaic Detector .............................................123