Full-physics carbon dioxide retrievals from the Orbiting Carbon Observatory-2 (OCO-2) satellite by only using the 2.06 µm band

• Main Authors: L. Wu, O. Hasekamp, H. Hu, J. aan de Brugh, J. Landgraf, A. Butz, I. Aben
• Format: Article
• Language: English
• Published: Copernicus Publications 2019-11-01
• Series: Atmospheric Measurement Techniques
• Online Access: https://www.atmos-meas-tech.net/12/6049/2019/amt-12-6049-2019.pdf

<p>Passive remote sensing of atmospheric carbon dioxide uses spectroscopic measurements of sunlight backscattered by the Earth's surface and atmosphere. The current state-of-the-art retrieval methods use three different spectral bands, the oxygen A band at <span class="inline-formula">0.76</span>&thinsp;<span class="inline-formula">µ</span>m and the weak and strong <span class="inline-formula">CO₂</span> absorption bands at <span class="inline-formula">1.61</span> and <span class="inline-formula">2.06</span>&thinsp;<span class="inline-formula">µ</span>m, respectively, to infer information on light scattering and the carbon dioxide column-averaged dry-air mole fraction <span class="inline-formula"><i>X</i>CO₂</span>. In this study, we propose a one-band <span class="inline-formula"><i>X</i>CO₂</span> retrieval technique which uses only the <span class="inline-formula">2.06</span>&thinsp;<span class="inline-formula">µ</span>m band measurements from the Orbiting Carbon Observatory-2 (OCO-2) satellite. We examine the data quality by comparing the OCO-2 <span class="inline-formula"><i>X</i>CO₂</span> with collocated ground-based measurements from the Total Carbon Column Observing Network (TCCON). Over land and ocean the OCO-2 one-band retrieval shows differences from TCCON observations with a standard deviation of <span class="inline-formula">∼1.30</span>&thinsp;ppm and a station-to-station variability of <span class="inline-formula">∼0.50</span>&thinsp;ppm. Moreover, we compare one-band and three-band retrievals over Europe, the Middle East, and Africa and see high correlation between the two retrievals with a SD of <span class="inline-formula">0.93</span>&thinsp;ppm. Compared to the three-band retrievals, <span class="inline-formula"><i>X</i>CO₂</span> retrievals using only the <span class="inline-formula">2.06</span>&thinsp;<span class="inline-formula">µ</span>m band have similar retrieval accuracy, precision, and data yield.</p>