Evaluating Recent Changes in Surface Elevation Models and Their Implications for the OCO-2 Bias Correction Over Northern High Latitude Regions

Knowledge of atmospheric CO2 concentrations in northern high latitude regions is important for developing a more holistic understanding of global carbon dynamics. The NASA Orbiting Carbon Observatory 2 (OCO-2) is a polar orbiting satellite with the ability to collect spatially and temporally dense observations in the northern high latitude (NHL) regions; however, many challenges continue to limit the amount of OCO-2 retrievals that meet good-quality standards in high latitude regions. Furthermore, unique radiative transfer effects in NHL regions warrant the consideration of a tailored bias correction for OCO-2 retrievals over NHLs. An essential component of the OCO-2 bias correction is a parametric adjustment based on the difference between retrieved surface pressure and prior surface pressure, which is also dependent on the Digital Elevation Model (DEM). As a result, an accurate DEM is essential for defining an appropriate bias correction for OCO-2 retrievals. There have been several recent updates to DEMs for NHL regions. Here, we compare the surface elevations used in the OCO-2 ACOS v10 retrievals to the following three new DEMs: JPL's NASADEM30plus as used in OCO-2 ACOS v11, which includes the first change to the referenced DEM since the initial implementation of the ACOS algorithm; the ArcticDEM, a project specifically dedicated to mapping surface elevations for regions north of 60°N latitude; and the Copernicus 30 m global DEM, made publicly available in 2021. We first evaluate each DEM's quality in NHL regions by comparing to different quality metrics, partially based on using OCO-2 surface pressure retrievals. Then, we calculate tailored bias corrections for OCO-2 B10 retrievals from NHL regions and explore how different DEMs impact the bias correction coefficients.