Remote Determination of Cloud Temperature and Transmittance from Spectral Radiance Measurements: Method and Results
DEFENCE RESEARCH ESTABLISHMENT VALCARTIER (QUEBEC)
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In this report a method for the evaluation of cloud temperature and transmittance from ground-based measurements of the downwelling spectral radiance is proposed. The method uses the strong emission band of ozone at 9.6 microns, which constitutes a natural source of IR radiation for probing clouds. Temperature and transmittance are derived from the cloudy sky radiance measured in two narrow spectral channels The first one is approximately at the center of the ozone band at 9.48 microns and the second one is off the band at 9.15 microns. The cloud parameters are found by solving a system of equations requiring, as input, an estimate of the cloud height and thickness obtained from lidar returns, and of atmospheric temperature and humidity profiles. The validation tests performed on experimental spectra demonstrate the accuracy of the method with typical temperature errors smaller than 2 K for the spectral measurements coincident in time with the lidar measurements. Finally, the main sources of method limitation are identified and analyzed.
- Numerical Mathematics
- Atomic and Molecular Physics and Spectroscopy