Fourier transform IR measurements of thermal infrared sky radiance and transmission

Charles L. Bennett

doi:10.1117/12.187560

30 September 1994 Fourier transform IR measurements of thermal infrared sky radiance and transmission

Charles L. Bennett

Proceedings Volume 2266, Optical Spectroscopic Techniques and Instrumentation for Atmospheric and Space Research; (1994) https://doi.org/10.1117/12.187560
Event: SPIE's 1994 International Symposium on Optics, Imaging, and Instrumentation, 1994, San Diego, CA, United States

Abstract

Precise relative measurements of sky continuum and line emission and absorption have been made using FTIR spectroscopy. During conditions of horizontally uniform air composition, measurements of the variation of the spectral radiance with elevation angle sample an air column that varies simply as the cosecant of the elevation angle. In spectral regions that are optically thin, an extrapolation to zero air mass can be used to accurately determine instrumental background. An ambient temperature black body reference furnishes an accurate measurement of the instrumental spectral response. The excess sky emission above instrumental background relative to the local black body reference spectrum thus provides a calibrated sky radiance spectrum. This spectrum can be used to calculate the atmospheric transmission. As a test, transmission spectra have been directly obtained with the full moon as a backlighting source, and are in excellent agreement with the sky radiance derived transmission spectra. For spectral regions dominated by water, the continuum emission has been measured for paths involving the entire atmospheric column. Reasonable agreement with previous laboratory measurements of the continuum strength is obtained.

Citation Download Citation

Charles L. Bennett "Fourier transform IR measurements of thermal infrared sky radiance and transmission", Proc. SPIE 2266, Optical Spectroscopic Techniques and Instrumentation for Atmospheric and Space Research, (30 September 1994); https://doi.org/10.1117/12.187560

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