Carbon dioxide retrieval from OCO-2 satellite observations using the RemoTeC algorithm and validation with TCCON measurements

• Main Authors: L. Wu, O. Hasekamp, H. Hu, J. Landgraf, A. Butz, J. aan de Brugh, I. Aben, D. F. Pollard, D. W. T. Griffith, D. G. Feist, D. Koshelev, F. Hase, G. C. Toon, H. Ohyama, I. Morino, J. Notholt, K. Shiomi, L. Iraci, M. Schneider, M. de Mazière, R. Sussmann, R. Kivi, T. Warneke, T.-Y. Goo, Y. Té
• Format: Article
• Language: English
• Published: Copernicus Publications 2018-05-01
• Series: Atmospheric Measurement Techniques
• Online Access: https://www.atmos-meas-tech.net/11/3111/2018/amt-11-3111-2018.pdf

In this study we present the retrieval of the column-averaged dry air mole fraction of carbon dioxide (<i>X</i>_CO₂) from the Orbiting Carbon Observatory-2 (OCO-2) satellite observations using the RemoTeC algorithm, previously successfully applied to retrieval of greenhouse gas concentration from the Greenhouse Gases Observing Satellite (GOSAT). The <i>X</i>_CO₂ product has been validated with collocated ground-based measurements from the Total Carbon Column Observing Network (TCCON) for almost 2 years of OCO-2 data from September 2014 to July 2016. We found that fitting an additive radiometric offset in all three spectral bands of OCO-2 significantly improved the retrieval. Based on a small correlation of the <i>X</i>_CO₂ error over land with goodness of fit, we applied an a posteriori bias correction to our OCO-2 retrievals. In overpass averaged results, <i>X</i>_CO₂ retrievals have an SD of  ∼ 1.30 ppm and a station-to-station variability of  ∼ 0.40 ppm among collocated TCCON sites. The seasonal relative accuracy (SRA) has a value of 0.52 ppm. The validation shows relatively larger difference with TCCON over high-latitude areas and some specific regions like Japan.