Optimization and accuracy validation of near-space 1.27 μm O ₂ (a ¹ Δg) dayglow forward model based on limb observation mode

The measurement of temperature and O3 concentration in the near-space region (20–100 km) holds significant scientific and practical value. The 1.27 μm O2(a1Δg) dayglow, characterized by high radiative intensity and broad spatial coverage, serves as an important tracer. Existing limb-viewing forward models suffer from inaccuracies in photochemical calculations and radiative transfer treatment, particularly due to simplified photodissociation coefficients and neglect of self-absorption and scattering. Consequently, large discrepancies arise between modeled and satellite-observed volume emission rates (VERs) in the 20–40 km range. An optimized forward model for 1.27 μm O2(a1Δg) limb-viewing observations is proposed. The variation of the photodissociation coefficient J3 with solar zenith angle (SZA) and altitude is explicitly calculated. Voigt line shapes are applied below 40 km to refine photon absorption coefficients g, thereby improving the precision of the photochemical model. The radiative transfer simulation incorporates both self-absorption and scattering effects. Validation shows that the simulated scattered absorption spectrum agrees well with the Moderate Resolution Atmospheric Transmission 5 (MODTRAN5) model, with a mean relative difference below 2%. Compared with Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) observations, the global mean relative difference of the simulated airglow integrated radiance is below 18.05% (23–100 km). Incorporating ozone profiles measured by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) further reduces the relative differences of local spectra to 6%. Inversion fitting based on the forward model yields mean relative differences of 2–5% between the fitted and SCIAMACHY-observed spectra. The mean residual between the retrieved and SABER temperature profiles is below 5 K. By incorporating both self-absorption and scattering processes into the radiative transfer model, this work establishes a more physically consistent forward model for the 1.27 μm O2(a1Δg) dayglow, enabling more accurate retrieval of atmospheric temperature and VER in the near-space region.