book06remsens - Weather Observation and Analysis John...

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Weather Observation and Analysis John Nielsen-Gammon Course Notes These course notes are copyrighted. If you are presently registered for ATMO 251 at Texas A&M University, permission is hereby granted to download and print these course notes for your personal use. If you are not registered for ATMO 251, you may view these course notes, but you may not download or print them without the permission of the author. Redistribution of these course notes, whether done freely or for profit, is explicitly prohibited without the written permission of the author. Chapter 6. REMOTE SENSING 6.1 Satellite Thermal Sounders The Earth is a planet covered by a blanket of warm gas. Except for when there are clouds, that blanket is nearly transparent to sunlight, which is how the ground heats up during the day. The Earth and its atmosphere are not hot enough to glow themselves, at least not that we can see. They do emit radiation depending on their temperature; it turns out to be mostly in the range of wavelengths we call infrared. One neat thing about the atmosphere is that, in the infrared range, different gases absorb and emit radiation at different wavelengths. (If a gas can absorb at a particular wavelength, it can emit there too.) So a satellite sensor out in space that detects infrared radiation might see a glowing ball of gas, if it’s tuned to a wavelength that a gas in the atmosphere absorbs and emits, or it might see radiation coming all the way from the Earth’s surface, if it’s tuned to a wavelength that no gas in the atmosphere touches. ATMO 251 Chapter 8 page 1 of 23
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