Abstract
Abstract. In this study, we present ground-based measurements of column-averaged dry-air mole fractions (DMFs) of CO2 (or XCO2) 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 XCO2 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 XCO2 scaling factor of 0.9954 relative to TCCON. Although we found a slight drift of 0.13 % over 3 months in the calibration curve of the EM27/SUN vs. TCCON XCO2, the alignment of the EM27/SUN proved stable enough for a 2-week campaign, keeping the retrieved Xair values, another measure of stability, to within 0.5 % and the modulation efficiency to within 2 %. From the measurements in Alice Springs, we confirm a small bias of around 2 ppm in the GOSAT M-gain to H-gain XCO2 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 https://doi.org/10.4225/48/5b21f16ce69bc (Velazco et al., 2018).
Highlights
The Greenhouse Gases Observing Satellite (GOSAT), launched on 23 January 2009, is the first satellite in orbit dedicated to the measurements of the two major anthropogenic greenhouse gases that cause global warming: CO2 and CH4 (Yokota et al, 2009; Kuze et al, 2009)
We present ground-based measurements of column-averaged dry-air mole fractions (DMFs) of CO2 taken in a semiarid region of Australia with an EM27/SUN portable spectrometer equipped with an automated clamshell cover
We found a slight drift of 0.13 % over 3 months in the calibration curve of the EM27/SUN vs. Total Carbon Column Observing Network (TCCON) XCO2, the alignment of the EM27/SUN proved stable enough for a 2-week campaign, keeping the retrieved Xair values, another measure of stability, to within 0.5 % and the modulation efficiency to within 2 %
Summary
The Greenhouse Gases Observing Satellite (GOSAT), launched on 23 January 2009, is the first satellite in orbit dedicated to the measurements of the two major anthropogenic greenhouse gases that cause global warming: CO2 and CH4 (Yokota et al, 2009; Kuze et al, 2009). GOSAT employs the different gain settings to compensate for the different signal levels due to the reflective properties (albedo) of the Earth’s surface, which depend on wavelength. These gain settings are prespecified at certain locations because GOSAT does not observe both M and H gains simultaneously.
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