Detection and Imaging of Methane Emissions Plumes from Oil and Gas Facilities with GHGSat-D

GHGSat-D is the first and only satellite on orbit designed for measurements of greenhouse gas emissions from individual industrial facilities. Launched in June 2016, its primary differentiating characteristic is spatial resolution of less than 50 metres. When the local column density near an observed emitter exceeds the background sufficiently, the resulting high-resolution retrieval fields consist of a spatially resolved "image" of the plume. Furthermore, our instrument concept essentially guarantees accurate geolocation of emissions signals within tens of metres.

Our instrument is based on an imaging Fabry-Perot spectrometer which does not produce a conventional spectrum. As a result, we use a novel retrievals technique where the emitter site of interest is captured in a sequence of overlapping two-dimensional images. The combined effect of the Fabry-Perot resonator and the scrolling scene gives a different spectral sampling of each surface location in every image. Crucially, the spectral properties of the instrument can be accurately characterized and modelled. As a result, our retrievals software is based on a forward model that predicts the per-pixel signal as a function of surface reflectance, atmospheric column densities and the instrument parameters.

The oil and gas sector is one of GHGSat's primary market segments and a large fraction of our measurement capacity is dedicated to measuring these sites. This is bolstered by significant customer interest in monitoring and quantifying fugitive emissions from their facilities. We present examples of GHGSat-D methane retrieval data from several such sites. We highlight our study of persistent, anomalously large methane leaks in Central Asia that we have been monitoring since 2018. Several such leaks were discovered by GHGSat in the form of strong, clear plume images consistently emanating from the same positions and whose directions were aligned with independent wind direction data. The same vicinity was examined in TROPOMI retrievals and was found to contain excess methane levels consistent with GHGSat's findings. From our observations we estimate emission rates in the range 10-42 tons h^-1 for the largest, most persistent source. This is of comparable magnitude to the well-documented Aliso Canyon and Ohio blowouts in 2015 and 2018 respectively.