Shipborne measurements of XCO<sub>2</sub>, XCH<sub>4</sub>, and XCO above the Pacific Ocean and comparison to CAMS atmospheric analyses and S5P/TROPOMI

Abstract

Abstract. Measurements of atmospheric column-averaged dry-air mole fractions of carbon dioxide (XCO2), methane (XCH4), and carbon monoxide (XCO) have been collected across the Pacific Ocean during the Measuring Ocean REferences 2 (MORE-2) campaign in June 2019. We deployed a shipborne variant of the EM27/SUN Fourier transform spectrometer (FTS) on board the German R/V Sonne which, during MORE-2, crossed the Pacific Ocean from Vancouver, Canada, to Singapore. Equipped with a specially manufactured fast solar tracker, the FTS operated in direct-sun viewing geometry during the ship cruise reliably delivering solar absorption spectra in the shortwave infrared spectral range (4000 to 11000 cm−1). After filtering and bias correcting the dataset, we report on XCO2, XCH4, and XCO measurements for 22 d along a trajectory that largely aligns with 30∘ N of latitude between 140∘ W and 120∘ E of longitude. The dataset has been scaled to the Total Carbon Column Observing Network (TCCON) station in Karlsruhe, Germany, before and after the MORE-2 campaign through side-by-side measurements. The 1σ repeatability of hourly means of XCO2, XCH4, and XCO is found to be 0.24 ppm, 1.1 ppb, and 0.75 ppb, respectively. The Copernicus Atmosphere Monitoring Service (CAMS) models gridded concentration fields of the atmospheric composition using assimilated satellite observations, which show excellent agreement of 0.52±0.31 ppm for XCO2, 0.9±4.1 ppb for XCH4, and 3.2±3.4 ppb for XCO (mean difference ± SD, standard deviation, of differences for entire record) with our observations. Likewise, we find excellent agreement to within 2.2±6.6 ppb with the XCO observations of the TROPOspheric MOnitoring Instrument (TROPOMI) on the Sentinel-5 Precursor satellite (S5P). The shipborne measurements are accessible at https://doi.org/10.1594/PANGAEA.917240 (Knapp et al., 2020).

Versatile and Targeted Validation of Space-Borne XCO2, XCH4 and XCO Observations by Mobile Ground-Based Direct-Sun Spectrometers

“…Since the first deployment in spring 2014 on RV Polarstern, the setup has substantially matured in terms of solar tracker performance and its ability to be remotely operated and to resist harsh weather. Klappenbach et al (Klappenbach et al, 2015) and Knapp et al (Knapp et al, 2021) report on ship deployments in the Atlantic and Pacific oceans which aimed at measuring meridional and zonal cross sections of background XCO 2 , XCH 4 and, for the latest instrument upgrade (Hase et al, 2016), XCO over the large oceans. Beside validating the satellite records from GOSAT, OCO-2, and S5P, our concentration records were also used for validating and improving a model used in the Copernicus Atmosphere Monitoring Service (CAMS) (Agusti-Panareda et al, 2017;Knapp et al, 2021).…”

“…Klappenbach et al (Klappenbach et al, 2015) and Knapp et al (Knapp et al, 2021) report on ship deployments in the Atlantic and Pacific oceans which aimed at measuring meridional and zonal cross sections of background XCO 2 , XCH 4 and, for the latest instrument upgrade (Hase et al, 2016), XCO over the large oceans. Beside validating the satellite records from GOSAT, OCO-2, and S5P, our concentration records were also used for validating and improving a model used in the Copernicus Atmosphere Monitoring Service (CAMS) (Agusti-Panareda et al, 2017;Knapp et al, 2021). The latest ship deployment took place in the Western Pacific and along the coast of Japan from February 13 to March 24, 2021 when the mobile EM27/SUN was operated onboard the Japanese RV Mirai (framed by a collaboration of Heidelberg University and the National Institute for Environmental Studies (NIES) of Japan).…”

“…A weather-proof housing hosts the FTS and solar tracker as well as various ancillary equipment such as the computers, ventilation units, and sensors for housekeeping data. Knapp et al (Knapp et al, 2021) describes the general setup in detail. Here, we focus on the solar tracker which is the unit enabling mobile applications and which has seen substantial improvements over the past years starting from the initial developments (Gisi et al, 2011;Klappenbach et al, 2015;Butz et al, 2017).…”

“…Another requirement for routine and autonomous operations is a weather-proof housing. We have developed such a system and demonstrated its performance for continuous operations on ships and for stop-and-go operations on small trucks (Klappenbach et al, 2015;Butz et al, 2017;Luther et al, 2019;Knapp et al, 2021). Section 2 reviews previous campaign deployments, Section 3 summarizes the key instrument parameters and reports on the processing recipe.…”

FTIR Measurements of Greenhouse Gases over Thessaloniki, Greece in the Framework of COCCON and Comparison with S5P/TROPOMI Observations

“…Both data products are filtered with a quality assurance value (qa) equal to 1.0, ensuring cloud-free observations. The data are constantly validated by the Mission Performance Center Validation Data Analysis Facility, VDAF, http://mpc-vdaf.tropomi.eu/ (accessed on 22 June 2021), who provide a quarterly validation report [34], as well as through recent TROPOMI-based validation papers (e.g., [28,35]). The S5P carbon monoxide and methane total column data are in overall good agreement with correlative measurements from the Network for the Detection of Atmospheric Composition Change (NDACC) and TCCON FTIR monitoring networks [36].…”