High-resolution methane mapping with the EnMAP satellite imaging spectroscopy mission

Methane mitigation from anthropogenic sources such as fossil fuels and waste management has been found as one of the most promising strategies to curb global warming in the near future. Satellite-based imaging spectrometers have demonstrated to be well-suited to detect and quantify these emissions at high spatial resolution. These instruments produce so-called hyperspectral data cubes of the solar radiation reflected by the Earth, measuring in the 400-2500 nm spectral range, with a spectral sampling of 5-15 nm and a spatial sampling of 30-60 m. Methane concentration enhancement maps are generated from those data cubes by leveraging spectral channels across the 2300 nm methane absorption window. The relatively high spatial resolution of the resulting methane maps allows for the detection and attribution of plumes to sources. The PRISMA satellite mission (ASI, Italy) hasbeen extensively used in the last years for this application. The recently-launched EnMAP mission (DLR/GFZ, Germany) presents similar spatial and spectral characteristics to PRISMA (30 m spatial resolution, 30 km swath, about 8 nm spectral sampling at 2300 nm) and can a priori thus be used for methane mapping as well.In this work, we investigate the potential and limitations of EnMAP for methane remote sensing, using PRISMA as a benchmark. First, we analyze the spectral and radiometric performance of EnMAP in the 2300 nm region used for methane retrievals, which includes parameters such as spectral uniformity and resolution and the signal-to-noise ratio (SNR). Our results show that in desertic areas at 2300 nm, EnMAP spectral resolution is about 2.7 nm smaller than in PRISMA and the SNR values are approximately twice as large, which leads to a higher sensitivity to methane that improves retrieval performance. This finding is illustrated by several show cases of methane plumes from different sources around the world with flux rate values ranging approximately from 1 to 20 t/h. We show plumes from sectors such as onshore oil and gas and coal mining, but also from more challenging sectors to detect such as landfills and offshore oil and gas. From the latter we detected two plumes with an unprecedented flux rate of about 1 t/h, which suggests that the detection limit in offshore areas can be significantly low under favorable conditions.