Reevaluating the Use of O 2 a 1 Δ g Band in Spaceborne Remote Sensing of Greenhouse Gases

Although the O 2 a 1 Δ g band has long been used in ground‐based greenhouse gas remote sensing to constrain the light path, it is challenging for nadir spaceborne sensors due to strong mesosphere/stratosphere airglow. Spectroscopic simulations using upper state populations successfully reconstruct the airglow spectra with excellent agreement with SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY limb observations (residual root‐mean‐square <0.7%). The accurate knowledge of airglow spectrum enables retrieval of O 2 ( a 1 Δ g ) number density, volume emission rate, and temperature. For nadir spaceborne observations, the a 1 Δ g airglow will lead to a negative bias of ∼10% to O 2 column, if not considered. However, when properly included, the airglow spectral feature can be adequately separated from O 2 absorption (mean bias <0.1%) at the spectral resolution of modern spaceborne spectrometers.