A Preliminary Study On The Vertical Profile Of Methane By Thermal Infrared Hyperspectral Retrieval

Methane (CH4) is one of the important Green house gases. But the emission of the CH4, the character of distribution and the quantitative description of feedbacks to the climate system response are still uncertain, due to the limited observation data. Traditional sparse ground based observations and not enough space coverage can’t meet the requirements of application. Data of satellite thermal infrared sensing can be used to monitor CH4 and Carbon dioxide (CO2). So Mastering the satellite detection principle and technology method of Green house gases in the study of thermal infrared remote sensing can supply technology preparation to study distribution principle of methane and has the practical significance to the research of global climate change and national response, etc.The inversion results are affected by atmospheric parameters such as atmospheric temperature and humidity profiles etc. and surface parameters, such as surface temperature and surface emissivity ect., by using thermal infrared methane profile inversion. Based on this, this paper first launched in the domestic research method of satellite thermal infrared remote sensing inversion of methane. Research contents and results are as follows:1. By using the CRTM radiative transfer model, the author respectively simulate and analyze the sensitivity of atmospheric temperature and humidity profiles and surface parameters between two spectral absorption band of CH4. Results show these factors can affect the atmospheric transmittance.2. The eigenvector regression algorithms presented which is a computationally efficient method for determining the distribution of methane from satellite sounding measurements uses previously determined statistical relationships between observed or simulated radiances with corresponding atmospheric profiles. It is more suitable to construct the a priori state.3. Demonstration and application in China. The focus of this study is to analyse spatial and temporal distribution characteristics of China near-surface CH4 concentration from 2003 to 2013 using the Atmospheric Infrared Sounder (AIRS) on the EOS/Aqua platform. Firstly, we use ground-based observation data from Waliguan (WLG) in Qinghai, Taiwan Lulinshan (LLN) and Ulaan Uul, Mongolia (UUM) to validate near-surface CH4 concentration of AIRS level 2 products. The results shows that near-surface CH4 concentration of AIRS has a consistent trend with ground-based sampling analysis. The correlation coefficients r is 0.69,0.5 and 0.64 respectively. Then from region, seasonal variation and inter-annual variations analysis spatial and temporal distribution characteristics of near-surface CH4 concentration in China. The results shows: (1) The minimum near-surface CH4 concentration is located in Tibet (-1800ppb) and the maximum is in northern Xinjiang, Inner Mongolia and northern HeiLongjiang (-1920ppb); (2) near-surface CH4 concentration is high in summer and low in winter. The seasonal change is significant, especially in the western region increased rapidly from 1838ppb in April to 1882ppb in September; (3) From 2003 to 2013, National average CH4 concentration near the ground has a basical growing trend expect for a slight decrease in 2006 and 2010. Northwest and east region vary consistently with the whole. The growth in northest China increaseed rapidly while in the south is not obvious and in northwest interannual fluctuations is bigger; (4) The error between AIRS near-surface CH4 products and ground-based observation data is less than 2%.