THERMAL INFRARED IMAGING OF THE ATMOSPHERE: THE INFRARED CLOUD IMAGER by Brentha Thurairajah A thesis submitted in partial fulfillment of the requirements of the degree of Master of Science in Electrical Engineering MONTANA STATE UNIVERSITY Bozeman, Montana April 2004 © COPYRIGHT by Brentha Thurairajah 2004 All Rights Reserved ii APPROVAL of a thesis submitted by Brentha Thurairajah This thesis has been read by each member of the thesis committee and has been found to be satisfactory regarding content, English usage, format, citations, bibliographic style, and consistency, and is ready for submission to the college of graduate studies. Dr. Joseph A. Shaw, Chair of Committee Approved for the Department of Electrical and Computer Engineering Dr. James N. Peterson, Department Head Approved for the College of Graduate Studies Dr. Bruce R. McLeod, Graduate Dean iii STATEMENT OF PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a master’s degree at Montana State University, I agree that the Library shall make it available to borrowers under the rules of the Library. If I have indicated my intention to copyright this thesis by including a copyright notice page, copying is allowable only for scholarly purposes, consistent with “fair use” as prescribed in the U.S Copyright Law. Requests for permission for extended quotation from or reproduction of this thesis in whole or in parts may be granted only by the copyright holder. Brentha Thurairajah April 2nd, 2004 iv ACKNOWLEDGEMENT I would like to thank my advisor Dr. Joseph Shaw for always being there, for guiding me with patience throughout the project, for helping me with my course and research work through all these three years, and for providing helpful comments and constructive criticism that helped me complete this document. I would also like to thank my committee members Dr. Bob Gunderson and Dr. Mark Ivey for their invaluable suggestions and comments. I wish to express my gratitude to the faculty and staff of the Electrical Engineering Department for their support and encouragement. I also wish to thank all the students at our Optical Remote Sensing Laboratory (ORSL) who helped in the working and successful deployment of the ICI, especially thanks to Nathan Pust for troubleshooting all the instrument problems and for keeping the ICI running successfully. I gratefully acknowledge the Japanese Communication Research Laboratory (CRL), National Oceanic and Atmospheric Administration/ Environmental Technology Laboratory (NOAA/ETL), and the Atmospheric Radiation and Measurement Program (ARM) for their funding, and support in deploying the Infrared Cloud Imager. Last but not the least I would like to thank my friends and family for their motivation and constant support. v TABLE OF CONTENTS 1. INTRODUCTION ...........................................................................................................1 2. CLOUDS AND CLOUD RADIATION..........................................................................9 CLOUD TYPES .................................................................................................................15 Importance of Cirrus clouds......................................................................................18 NORTH SLOPE OF ALASKA AND THE SOUTHERN GREAT PLAINS ...................................19 3. THE INFRARED CLOUD IMAGER ...........................................................................23 INTRODUCTION........................................................................................................................23 HARDWARE ..............................................................................................................................24 The Infrared Camera.................................................................................................26 Blackbody and Blackbody Controller.......................................................................29 Mirror........................................................................................................................30 SOFTWARE................................................................................................................................30 CALIBRATION ..........................................................................................................................33 Recalibration.............................................................................................................35 ICI IMAGES .....................................................................................................................36 4. RADIATIVE TRANSFER ANALYSIS........................................................................40 INTRODUCTION ..............................................................................................................40 BARROW WATER VAPOR CORRECTION ..........................................................................44 OKLAHOMA WATER VAPOR CORRECTION .....................................................................48 WATER VAPOR INFORMATION .......................................................................................50 Measuring Surface Vapor Density............................................................................50 Tomasi’s Equation ....................................................................................................52 THRESHOLDS..................................................................................................................54 Barrow Comparison..................................................................................................54 Oklahoma Comparison ..............................................................................................57 5. RESULTS ......................................................................................................................65 CLOUD STATISTICS .......................................................................................................65 Barrow Experiment ..............................................................................................................66 Oklahoma Experiment .........................................................................................................69 TAYLOR’S HYPOTHESIS .................................................................................................72 Barrow Results..........................................................................................................73 Oklahoma Results .....................................................................................................75 vi TABLE OF CONTENTS – CONTINUED CLOUD TYPE ..................................................................................................................78 COMPARISON OF CLOUDS MEASURED WITH OTHER SENSORS .....................................81 6. CONCLUSION AND RECOMMENDATIONS ..........................................................88 REFERENCES CITED......................................................................................................91 APPENDIX: GLOSSARY OF ACRONYMS...................................................................95 vii LIST OF TABLES Table Page 2.1. The Ten Cloud Genera.........................................................................................16 4.1. Air Temperature Profile at Multiples of Scale Height......................................................................................................46 viii LIST OF FIGURES Figure Page 2.1. Downwelling Spectral Radiance of a Clean Atmosphere 1976 US Standard Atmosphere Model ..............................................................10 2.2. Atmospheric Water Vapor Profile: Exponential and Inversion............................12 2.3. Spectral Radiance of Clear Sky and Stratus Cloud...............................................17 2.4. Transmittance and Radiance.................................................................................20 2.5. Spectral Radiance for Two Different Atmospheric Conditions............................21 3.1. ICI Block Diagram................................................................................................24 3.2. ICI Internal View ..................................................................................................25 3.3. Sequence of ICI Operations..................................................................................30 3.4. Calibration Data with ICI Viewing a Blackbody Cone Immersed in Alcohol Cooled with Dry Ice........................................................35 3.5. Images from the ICI..............................................................................................37 4.1. The Different Components of the Measured Downwelling Radiance.............................................................................................................41 4.2. Downwelling Atmospheric Emission in the 8-14 µm Band as a Function of Total Atmospheric Water Vapor.............................................44 4.3. Air Temperature as a Function of Altitude...........................................................46 4.4. Error from Subtraction Total Water Vapor Column, Plotted Versus the Band-integrated (8-14 µm) Radiance of a Blackbody Cloud at the Air Temperatures Shown in Table 4.1 and Figure 4.2 ...................................................................................47 4.5. Downwelling Radiance as a Function of PWV for Different Surface Air Temperatures................................................................................