Retrieving Atmospheric Water Vapor Content Based on Absolute Brightness of Sky Background Spectral Radiation

摘要

To get the knowledge of sky background spectral radiance and its usage in retrieving atmospheric parameters, a wide-spectrum fiber spectrophotometer was calibrated with the field view of one degree. An experiment was performed at the fine days after a heavy snow weather process, and the horizontal spectral radiance direct to the south was measured periodically during the whole days. We found that when the sky was fine, the short-wavelength sky radiance was significantly higher than the long-wave band. This is because the intensity of the scattered light is inversely proportional to the fourth power of the wavelength. A sunny day with red sky in the morning, the snow began to melt., the short-wavelength sky background radiance was lower than the long-wavelength band. The absorption band of water vapor in the spectral data is apparent, which implies the possibility of retrieving atmospheric water vapor content from these data. Using MODTRAN, the Continuum Interpolated Band Ratio (CIBR) near the 940nm water absorption bandwidth was estimated, and the water vapor column concentration was retrieved. Comparison the results with what was measured by the POM2 sun radiometer show satisfied consistence. The method of retrieving water vapor content from the background spectral radiance provide us a way to have a deeper understanding of the absolute radiance of the sky background.