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Remote Sensing of Greenhouse Gases for Carbon Cycle Modelling

Fachliche Zuordnung Physik und Chemie der Atmosphäre
Förderung Förderung von 2011 bis 2018
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 183111364
 
Erstellungsjahr 2016

Zusammenfassung der Projektergebnisse

The ‘RemoteC’ project aimed at an improved understanding of the processes controlling the abundances of the greenhouse gases carbon dioxide (CO2 ) and methane (CH4 ) in the Earth’s atmosphere. The key contribution made was the exploration of advanced remote sensing applications to enhance the accuracy and the spatiotemporal density of CO2 and CH4 concentration measurements to be fed into models for source/sink estimation. Instrumental, algorithmic, and modeling techniques were further developed, scientific insight into the functioning of biogeochemical cycles and anthropogenic sources was gained through case studies. We established the ‘RemoTeC’ satellite algorithm as a world-leading radiative transfer tool for the retrieval of greenhouse gas concentrations from satellites such as the Greenhouse Gases Observing Satellite (GOSAT) and the Orbiting Carbon Observatory (OCO-2). Comparison to groundbased observations within the Total Carbon Column Observing Network (TCCON) showed that accuracy of the RemoTeC satellite records was promising for assessing source/sink processes. We further examined future satellite missions such as ESA’s Sentinel-5 Precursor and Sentinel-5 with respect to their prospective performance and capabilities. The Geostationary Emission Explorer for Europe (G3E) was developed as a concept for a future greenhouse gas satellite in geostationary orbit that would provide a leap forward in observation density. For ground-based greenhouse gas observations, we aimed at developing a prototype grating spectrometer and we contributed to the improvement of the small Fourier Transform spectrometer EM27/SUN. Both spectrometers were deployed on the German Research vessel Polarstern in order to monitor CO2 and CH4 concentrations over the Atlantic during a cruise (March 8 through April 13, 2014) from Capetown, South Africa, to Bremerhaven, Germany. While the grating spectrometer was found to require further improvements, the EM27/SUN achieved outstanding accuracy. The latitudinal transect of XCO2 and XCH4 in particular contributed to improving the interhemispheric transport in the CAMS (Copernicus Atmospheric Monitoring Service) model run by ECMWF (European Centre for Medium range Weather Forecasts). Another field deployment of the EM27/SUN in the vicinity of the Mt. Etna volcano, Sicily, (Sep. 5 through Sep. 25, 2015) allowed for successful remote detection of the volcanic CO2 emissions, together with volcanic emissions of hydrogen fluoride, hydrogen chloride, sulphur dioxide and bromine monoxide. The latter two gases were measured by a co-mounted UV spectrometer. These field-deployments clearly recommend the EM27/SUN spectrometers for use in regional and global emission monitoring applications. The remote sensing data streams were examined for source/sink signals. Thereby, we focused on the year-to-year and seasonal variability of CO2, e.g. for the Eurasian heatwave 2010, the seasonal cycle amplitude in South-East Asia, and an anomalous greening period in Australia. For CH4 , our GOSAT retrievals supported an upward trend in US American methane emissions of about 30% over the last decade. Methodologically, we focused on comparing two state-of-the-art CO2 inverse modelling systems, CarbonTracker and TM5-4DVar. Comparison of the two systems revealed that differences were most pronounced in regions where sparseness of observational constraints amplified the effect of choices in model setup. For North America, the current in-situ network coverage allowed for robust surface flux estimates on the sub-continental scale. Overall, our project suggests that a) gaining knowledge on carbon (CO2 and CH4 ) sources and sinks with regional and monthly resolution requires denser-than-present observation coverage and b) satellite and ground-based remote sensing techniques are sufficiently mature to deliver insight into sources and sinks. Nevertheless, a break-through toward regional-scale flux monitoring based on satellite observations still needs to be demonstrated, for example, by upcoming satellite missions with improved spatial sampling density.

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