Accurate mobile remote sensing of XCO<sub>2</sub> and XCH<sub>4</sub> latitudinal transects from aboard a research vessel

Abstract

Abstract. A portable Fourier Transform Spectrometer (FTS), model EM27/SUN, is deployed onboard the research vessel Polarstern to measure the column-average dry air mole fractions of carbon dioxide (XCO2) and methane (XCH4) by means of direct sunlight absorption spectrometry. We report on technical developments as well as data calibration and reduction measures required to achieve the targeted accuracy of fractions of a percent in retrieved XCO2 and XCH4 while operating the instrument under field conditions onboard the moving platform during a six week cruise through the Atlantic from Cape Town (South Africa, 34° S, 18° E) to Bremerhaven (Germany, 54° N, 19° E). We demonstrate that our solar tracker typically achieves a tracking precision of better than 0.05° toward the center of the sun throughout the ship cruise which facilitates accurate XCO2 and XCH4 retrievals even under harsh ambient wind conditions. We define several quality filters that screen spectra e.g. when the field-of-view is partially obstructed by ship structures or when the lines-of-sight cross the ship exhaust plume. The measurements in clean oceanic air, can be used to characterize a spurious airmass dependency. After the campaign, deployment of the spectrometer side-by-side the TCCON (Total Carbon Column Observing Network) instrument at Karlsruhe, Germany, allows for determining a calibration factor that makes the entire campaign record traceable to World Meteorological Organization (WMO) standards. Comparisons to observations of the GOSAT satellite and concentration fields modeled by the European Centre for Medium-Range Weather Forecasts (ECMWF) within the project Monitoring of Atmospheric Composition and Climate – Interim Implementation (MACC-II) demonstrate that the observational setup is well suited to provide validation opportunities above the ocean and along interhemispheric transects.

Calibration and instrumental line shape characterization of a set of portable FTIR spectrometers for detecting greenhouse gas emissions

“…We find a systematic scaling factor of 0.9700 between these records and the barometric ground pressure. This factor was calculated with the method described in the previous section and is in good agreement with other observations or Klappenbach et al, 2015. Its origin can mainly be attributed to oxygen line intensity errors (Washenfelder et al, 2006).…”

“…The data set it is not well suited for this task due to I n s t r u m e n t 1 I n s t r u m e n t 2 I n s t r u m e n t 3 I n s t r u m e n t 4 I n s t r u m e n t 5 T C C O N I n s t r u m e n t the actual intraday variability which occurred. Instead we use parameters obtained from a comprehensive evaluation of EM27/SUN data from a ship cruise (Klappenbach et al, 2015). These data are not influenced by local source contributions and clearly show the SZA dependency in the XCO 2 and XCH 4 data.…”

“…The spectrometer is now available from Bruker under the part name EM27/SUN. This lightweight device has low infrastructure demands so it can be operated on a campaign basis, at remote places and even on mobile platforms such as ships (Klappenbach et al, 2015). These features not only enable the EM27/SUN to contribute to the total column measurements of the TCCON in previously underrepresented regions, in particular it can be used to gain additional information about isolated sinks and sources of greenhouse gases.…”

Intercomparability of X<sub>CO<sub>2</sub></sub> and X<sub>CH<sub>4</sub></sub> from the United States TCCON sites

“…This complicated the separation of the spurious effects with AM from true atmospheric variation. Additional measurements in areas with little atmospheric variation could aid in accounting for AM artifacts (Klappenbach et al, 2015). In this study, we apply a symmetric basis function to the mFTS products following Eq.…”

Automated Enclosure and Protection System for Compact Solar-Tracking Spectrometers

“…While the large IFS 125HRs are deployed for global observations, as done by TCCON, the small EM27/SUNs are more often utilized for local and city source investigations ; Chen et al (2016) ;Franklin 15 et al (2016); Viatte et al (2017); Chen et al (2017)). Further, it has been deployed on a ship (Klappenbach et al (2015)) and in a mobile observatory to assess volcanic emissions ). However, up to this day a lot of human manpower is necessary to operate the instrument at the measurement site.…”