Calculation of the absorption coefficient of air at different heights using the HITRAN and ACE-FTS databases

Subject of study. Increasing requirements for the accuracy of modeling the brightness characteristics of the atmos-phere at different heights motivate the development of more detailed methods for the calculation of the absorption coefficient of air. Method. Modern databases of satellite sounding of the atmosphere that contain information on the volume fractions of air components at different heights in combination with a database of the parameters of the spectral lines of gases can be used in this task to calculate the spectral absorption coefficient. The possibility of specifying the geographic position of the height profiles of the air components (by specifying latitude and longi-tude) is an additional advantage of using the databases of satellite sounding. This method enables the differences in air compositions above different regions of the Earth to be considered. These databases usually provide information starting from a certain height; thus, databases of satellite sounding must be combined with the data obtained either from ground-based meteorological stations or using model distributions. The ACE-FTS database was used in this study, and it was combined with the standard atmosphere MODTRAN models at low heights. A filter for the ACE-FTS database was implemented using C++. The HITRAN database was used to calculate absorption coefficients. The ACE-FTS database provides data for 43 components of air, and the HITRAN database contains data for line -by-line calculation for 27 of these components and data on spectral absorption cross-sections for the remaining 16 components. Main results. A program for the calculation of the absorption coefficient of a multicomponent gas mixture was developed using C++. A Voigt profile was used in the line-by-line calculation, the effects of pres-sure and temperature on the line shift were considered, and line broadening owing to the following processes was considered: self-broadening, broadening resulting from interaction with water and carbon dioxide molecules, and broadening owing to interaction with other components of the air. The software explicitly considers the isotopic composition of molecules, thus enabling the calculation of not only the air mixture but also an arbitrary mixture with specified isotopic composition, information on which is in the HITRAN database. Moreover, the data of the high-temperature version HITEMP are considered. Practical significance. The combination of the ACE-FTS and HITRAN databases enables the calculation of a detailed profile of the spectral absorption coefficient of air for the specified month, temperature at the surface of the Earth, and geographic latitude and longitude, thus increasing the information content of the input data for the calculation of the brightness and transmission of the atmosphere at different heights. The data readout rate (parsing) and calculation speed of the developed program and the program HAPI implemented using Python are compared.(c) 2023 Optica Publishing Group