Exciting prospects for the IMAU/SRON remote sensing group
On July 2nd, 2014, NASA brought the new Orbiting Carbon Observatory (OCO-2) satellite into orbit. This new instrument measures carbon dioxide (CO2) in the atmosphere and complements the Japanese Greenhouse Gas Observing Satellite (GOSAT), which since 2009 has been measuring the greenhouse gases CO2 and methane (CH4). Back then, the Japanese and American space agencies were in competition to launch the first space-born CO2 sensor for studying the carbon cycle. While the Japanese were successful, the Americans saw their mission end up in the Southern Ocean due to problems with the launcher. Now, five years later, the rebuilt satellite made it successfully into space.
Scientists at IMAU and SRON are part of the international effort to constrain carbon emissions using data from GOSAT and OCO-2. These satellites measure total gas content in the atmospheric column. With help of atmospheric transport models and inverse modeling algorithms, the measured column abundances are translated into surface emissions. Because of the long lifetime of CO2 in the atmosphere, the signals of fresh emissions only show up as small ripples superimposed on a high background value. The challenge is to bring the precision and accuracy of the spaceborn instruments to a level at which these ripples can be resolved.
The GOSAT data enabled us to greatly improve the retrieval methods that translate satellite observed spectral radiances into CO2 and CH4 column concentrations. However, the spatial coverage remained limited, because of the long time needed for a single measurement. The new ‘grating’ spectrometer onboard the OCO-2 satellite measures much quicker, which will result in a much-improved spatial coverage. That is why we expect the OCO-2 satellite to shed further light on components of the global carbon cycle, such as the fate of ~50% of the emissions from fossil fuel use, which is absorbed by the oceans and the terrestrial biosphere. The latter component of the global carbon cycle is still poorly understood, in particular the impacts of climate change and carbon dioxide fertilization on the functioning of ecosystems at different latitudes.
Besides constraining natural feedbacks in the carbon cycle, OCO-2 may well turn out to be a powerful tool also for constraining regional fossil fuel emissions. For instance, the plumes of megacities are expected to show up in the data. There is a great interest in quantifying city scale emissions, especially in rapidly developing countries. At IMAU, the first steps are being made in preparation of such novel applications of spaceborne greenhouse gas measurements.
Sander Houweling, scientist at IMAU and SRON (Netherlands Institute for Space Research)