Mapping methane point emissions with the PRISMA spaceborne imaging spectrometer

The detection of methane emissions from fossil fuel production activities, such as oil and gas extraction and coal mining, has been identified as a key means for the reduction of greenhouse gas emissions to the atmosphere. Several types of optical satellite sensors have recently been shown to be instrumental for this task. Spaceborne imaging spectrometers belong to this group. These instruments measure the solar radiation reflected by the Earth in hundreds of spectral channels in the 400-2500 nm spectral range with a typical spectral resolution of 10 nm and a spatial resolution of 30 m. The Italian PRISMA mission is the first system of this type providing data openly to the international scientific community. In this work, we evaluate the potential of PRISMA for methane mapping. Our retrieval of methane concentration enhancements is based on a matched-filter based algorithm applied to the 2300 nm spectral region containing methane absorption bands. We perform a simulation-based sensitivity analysis to assess the retrieval performance for different sites. The impact on the retrieval of uncertainties in PRISMA's spectral response and of different illumination conditions has also been evaluated. We find that brightness and homogeneity of the surface are major drivers for the detection and quantification of methane plumes with PRISMA, with precision errors ranging from 61 to 197 ppb in the evaluated images. The potential of PRISMA for methane mapping is further illustrated by real plume detections at different methane hotspot regions, including oil and gas extraction fields in Algeria, Turkmenistan, and the Permian Basin (USA) as well as the coal mines in the Shanxi region in China. Our study reports several important findings regarding the potential and limitations of PRISMA for methane mapping, most of which can be extrapolated to upcoming satellite imaging spectroscopy missions.