Satellite and ground-based measurements of XCO₂ in a remote semiarid region of Australia

• Main Authors: V. A. Velazco, N. M. Deutscher, I. Morino, O. Uchino, B. Bukosa, M. Ajiro, A. Kamei, N. B. Jones, C. Paton-Walsh, D. W. T. Griffith
• Format: Article
• Language: English
• Published: Copernicus Publications 2019-07-01
• Series: Earth System Science Data
• Online Access: https://www.earth-syst-sci-data.net/11/935/2019/essd-11-935-2019.pdf

<p>In this study, we present ground-based measurements of column-averaged dry-air mole fractions (DMFs) of <span class="inline-formula">CO₂</span> (or <span class="inline-formula">XCO₂</span>) taken in a semiarid region of Australia with an EM27/SUN portable spectrometer equipped with an automated clamshell cover. We compared these measurements to space-based <span class="inline-formula">XCO₂</span> retrievals from the Greenhouse Gases Observing Satellite (GOSAT). Side-by-side measurements of EM27/SUN with the Total Carbon Column Observing Network (TCCON) instrument at the University of Wollongong were conducted in 2015–2016 to derive an <span class="inline-formula">XCO₂</span> scaling factor of 0.9954 relative to TCCON. Although we found a slight drift of 0.13&thinsp;% over 3 months in the calibration curve of the EM27/SUN vs. TCCON <span class="inline-formula">XCO₂</span>, the alignment of the EM27/SUN proved stable enough for a 2-week campaign, keeping the retrieved <span class="inline-formula">X_air</span> values, another measure of stability, to within 0.5&thinsp;% and the modulation efficiency to within 2&thinsp;%. From the measurements in Alice Springs, we confirm a small bias of around 2&thinsp;ppm in the GOSAT M-gain to H-gain <span class="inline-formula">XCO₂</span> retrievals, as reported by the NIES GOSAT validation team. Based on the reported random errors from GOSAT, we estimate the required duration of a future campaign in order to better understand the estimated bias between the EM27/SUN and GOSAT. The dataset from the Alice Springs measurements is accessible at <a href="https://doi.org/10.4225/48/5b21f16ce69bc">https://doi.org/10.4225/48/5b21f16ce69bc</a> <span class="cit" id="xref_paren.1">(<a href="#bib1.bibx28">Velazco et al.</a>, <a href="#bib1.bibx28">2018</a>)</span>.</p>