Supplement to: Comparison of Optimal Estimation HDO/H2O Retrievals from AIRS with ORACLES measurements

In this supplement we assess the sensitivity of HDO and H2O retrievals to the choice of forward model. All the retrievals in this paper were obtained from the MUSES retrieval framework using the Optimal Spectral Sampling (OSS) forward model (Moncet et al., 2008, 2015). The OSS method was designed specifically for the modeling of radiances measured by sounding radiometers in the infrared (Moncet et al., 2008, 2015), although it is applicable throughout the microwave, visible, and ultraviolet spectral regions. OSS uses an extension of the exponential sum fitting of transmittances technique in that channel-average radiative transfer is obtained from a weighted sum of monochromatic calculations. Among the advantages of the OSS method is that its numerical accuracy, with respect to a reference line-by-line model, is selectable, allowing the model to provide whatever balance of accuracy and computational speed is optimal for a particular application. Only a few monochromatic points are required to model channel radiances with a brightness temperature accuracy of 0.05 K. The version of OSS used here is trained with the monochromatic Atmospheric and Environmental Research, Inc. (AER) Line-By-Line Radiative Transfer Model (LBLRTM_v12.4) (Clough et al., 2005) using spectroscopic parameters from the ‘HIgh-resolution TRANsmission’ database (HITRAN12) (Rothman et al., 2013) plus line coupling coefficients for CO2 and CH4 calculated at AER.