Influence of environmental parameters on quantifying point-source emissions of CO2 and CH4 from observations of the future DLR satellite mission CO2Image

Abstract

Over the last decades climate observations show an increase of global land and sea surface temperature. As there is scientific consensus that the dominant cause of this global warming is the increase in anthropogenic greenhouse gas (GHG) emissions, countries must report their GHG emissions to the United Nations Framework Convention on Climate Change (UNFCCC). The CO2Image mission of the German Aerospace Center (DLR) with a spatial resolution of 50 x 50 m2 will be able to observe specifically large and medium-sized point sources, which are responsible for around 88% of the global CO2 emissions. The independent verification of reported emissions through CO2Image will be a great contribution to mitigate climate change. This thesis examines the impact of scattering due to aerosols on the reflected solar radiation in the shortwave infrared (SWIR) spectrum which is measured by the CO2Image instrument. To investigate the influence of aerosol scattering on the quantification of emitted CO2, this work performs simulations based on the retrieval algorithm RemoTeC by varying values for the parameters of the aerosol optical thickness, aerosol height and size distribution. This leads to the result that for a spatial resolution of 50 x 50 m2 scattering due to aerosols can be neglected if the aerosols are homogenously dispersed over the whole scene and the location and size of the plume is known. Contrarily, if there is no knowledge about the location and size of the plume, the automatic plume detection fails to find the entire plume and thus the CO2 concentration is underestimated. However, if the aerosol optical thickness, aerosol height or aerosol size only changes inside the plume and the background still has a low aerosol amount, significant errors occur. As aerosol scattering shortens the light path of the measured reflected solar radiation, the integrated mass enhancement (IME) is underestimated. Hence, with increasing values for the three aerosol parameters the true CO2 concentrations are significantly underestimated for a heterogeneous aerosol scenario. Furthermore, a strong correlation of the surface albedo with the errors in the retrieved CO2 was found. While dark surfaces reinforce the underestimation of the true CO2 due to aerosol scattering, bright surfaces can be a mediator for errors caused by aerosol scattering.