Effect of temperature-dependent cross sections on O-4 slant column density estimation by a space-borne UV-visible hyperspectral sensor

Abstract

The sensitivities of oxygen dimer (O-4) slant column densities (SCDs) were examined by applying temperature-dependent O-4 cross sections using the radiative transfer model (RTM) calculation with the linearized pseudo-spherical vector discrete ordinate radiative transfer model. For the sensitivity study, we used a newly developed cross section database in place of the database used in the operational algorithm. Newly investigated O-4 cross section databases for 203 K and 293 K were used for the radiance simulation by interpolating temperature for each atmospheric layer based on the vertical profile of standard atmosphere in the RTM. The effect of the temperature-dependent cross sections was a significant O-4 SCD increase of 8.3% with dependence on satellite and solar viewing geometries. Furthermore, the O-4 SCD generally increased by an estimated 3.9% based on the observation geometries of the Ozone Monitoring Instrument. For the long-term comparison, the O-4 SCD estimated from the temperature-dependent cross sections corrects 20% of the total underestimation of O-4 SCD between the observation and simulation. Although the surface pressure variation and background aerosol effect also correct the O-4 SCD discrepancy, the effect of temperature-dependent cross sections was more important than the effects of surface pressure variation and background aerosols. Therefore, temperature dependence of the cross section in the RTM calculation is essential for the accurate simulation of O-4 SCD.