The impact of non-zenith elevation angles on ground-based infrared thermodynamic retrievals.

Observing thermodynamic profiles within the planetary boundary layer is essential to understanding and predicting atmospheric phenomena due to the significant exchange of sensible and latent heat between the land and atmosphere within that layer. The Atmospheric Emitted Radiance Interferometer (AERI) is a ground-based infrared spectrometer used to obtain the vertical profiles of temperature and water vapor mixing ratio. Most AERIs are only capable of zenith views, though the Marine AERI (M-AERI) has a design that allows it to view various elevation angles. In this study, we quantify the improvement in the information content and accuracy of the retrieved profiles when non-zenith angles are included, as is common with microwave radiometer profilers. The impacts of the additional scan angles are quantified through both a synthetic study and with M-AERI observations from the ARM Cloud Aerosol Precipitation Experiment (ACAPEX) campaign. The simulation study shows low elevation angles contain more information content for temperature while high elevation angles have more information content for water vapor. Outside of very humid environments, the addition of low elevation angles also results in lower root mean square errors when compared to high angles for both temperature and water vapor mixing ratio, although this is primarily a result of averaging multiple observations together to reduce instrument noise. Real-world results from the ACAPEX data set indicate similar results as the simulation study, although not all predicted benefits are realized due to the small sample size and observation uncertainties.