The Build Of Absorption Coefficients Lookup Table For The Tansate’s Retrieval Of XCO₂

The absorption cross section table is built for the Tansat Satellite of China which isdesigned to map carbon sources and storage sinks. And during the calculation, we considerand analyze the effects of LM(Line Mixing) and CIA (Collision Induced Absorption) of CO2and O2.The Voigt profile is used to calculate absorption cross section of CH4, H2O, CO2, O2, andthe continuous absorption of H2O, LM of CO2, LM and CIA of O2are alsoconsidered.The results show that LM effect leads to an underestimation of absorption at peaks and anoverestimation at wings. The relative contribution on CO2absorption by LM is around2%,while at trough and right wing of R branch, it is over4%. The ratio of LM contribution ishigher at wings. As for the spectrum, LM effect mainly narrows the branches with theabsorption band shifting toward center. The absorption intensifies at peaks and weakens atwings. The LM effect of O2is similar with CO2and the CIA effect shows an smoothcorrection imposed on LM. The relative effect of O2is75%on the left wings of the branch,the LM and CIA of O2also decrease the systematic structures near13167cm-1in the fitresiduals obviously.Meanwhile, we analyzed the variation of absorption coefficients with pressure andtemperature. The absorption at central lines increases with the pressure arising while decreasesat wings. Not only the intensity varies with temperature, but also the shapes of absorption lines.The P and R branch shift toward each other with the temperature decreasing. After the analysison the variation of absorption coefficients with pressure, temperature and wavenumber, webuild up the three-dimensional ABSCO,in which the error of the interpolation is less than0.1%.The interval of temperature is8K, and the interval of pressure is15hPa. The interval ofwavenumber of O2is0.001cm-1, and for other absorption gas (H2O、CH4、CO2) it is0.002cm-1.The temperature of ABSCO ranges from174K to334kK, and the pressure rangesfrom10-8hPa to1025.00hPa, the ranges of wavenumber are4780-4920cm-1、6130-6300cm-1、 12830-13200cm-1.We use liner interpolation for pressure and wavenumber dimensions, andcubic spline interpolation for temperature dimension.In the end, the database of HITRAN12and HITRAN08are compared, and is it found thatthe total absorption of O2and CO2have little changes, but the total intensity of absorption andthe number of lines of H2O and CH4have a remarkable change.