Column abundance of atmospheric CH4 and precipitable water measurements from ground-based infrared solar spectra

Heli Wei; Qinghong Liu; Qingshan Xu; Fengsheng Zhao; Zhengfang Song

doi:10.1117/12.317732

18 August 1998 Column abundance of atmospheric CH₄ and precipitable water measurements from ground-based infrared solar spectra

Heli Wei, Qinghong Liu, Qingshan Xu, Fengsheng Zhao, Zhengfang Song

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Proceedings Volume 3501, Optical Remote Sensing of the Atmosphere and Clouds; (1998) https://doi.org/10.1117/12.317732
Event: Asia-Pacific Symposium on Remote Sensing of the Atmosphere, Environment, and Space, 1998, Beijing, China

Abstract

Infrared solar spectra were measured automatically by an infrared solar spectrometer (ISS) capable of 0.4 cm^-1 resolution. Good signal-o-noise ratio (SNR) and relatively high resolution made it possible to select unsaturated, temperature insensitive intervals for a specific absorption gas with minimal overlap by other interfering gases. In the wavelength range of 3.410-3.438μm, the absorption is mainly due to atmospheric methane and water vapor. A line-by-line (LBL) computation method was used to calculate theoretical atmospheric absorption. By adjusting the total column density to obtain an exact agreement between the calculated and observed absorption, the total column density of atmospheric methane and water vapor were obtained. In the paper, some result observed by ISS for more than one year were reported. Since the April of 1997, we have been monitoring the column abundances of atmospheric CH₄ and H₂O continually on every clear cloudless day with the method indicated above. The results show that CH₄ has little variation in one day, but has considerable seasonal variation. More than one high density peaks were found, two of which occurred in hot summer and cold winter, and the smallest value was found in spring. The reason is explained as emissions of local sources and atmospheric transport. The precipitation of column water vapor has a largely variation even in one day, the smallest precipitation appeared in winter, the biggest value was found in hot summer, seasonal variation could be as large as 40 times.

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Heli Wei, Qinghong Liu, Qingshan Xu, Fengsheng Zhao, and Zhengfang Song "Column abundance of atmospheric CH₄ and precipitable water measurements from ground-based infrared solar spectra", Proc. SPIE 3501, Optical Remote Sensing of the Atmosphere and Clouds, (18 August 1998); https://doi.org/10.1117/12.317732

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KEYWORDS

Methane

Absorption

Infrared radiation

Gases

Signal to noise ratio

Infrared spectroscopy

Atmospheric monitoring

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