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

Abstract

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.

Multi-satellite data depicts record-breaking methane leak from a well blowout

“…The resulting water vapour maps show the expected turbulence patterns, but no water vapour plume superposed to the methane plumes. Also, we do not detect any smoke signal in the 2300 nm spectral window used for the methane retrievals, indicating that the smoke plumes may not have a relevant optical activity in this spectral range for this event, which has also been found in previous studies 10 .…”

“…In contrast, the hyperspectral high-resolution missions have a sparse spatiotemporal sampling as compared with TROPOMI, but scan the Earth at a much higher spatial resolution, which enables the detection of smaller plumes and the attribution of those to facility-level sources. Among these hyperspectral high-resolution missions we find the GHGSat private constellation 7;8 , specifically designed for methane and carbon dioxide mapping at 25-50 m resolution, and the EnMAP, PRISMA and EMIT scientific missions, which also have a relatively high sensitivity to methane [9][10][11] . Finally, the Sentinel-2 and Landsat multispectral radiometers offer a lower sensitivity to methane than the hyperspectral missions, but have a 20-30 spatial sampling and a systematic global coverage every few days [12][13][14] , which compensates for the sporadic and under-demand sampling of the hyperspectral satellites.…”

Offshore methane detection and quantification from space using sun glint measurements with the GHGSat constellation

“…Offshore methane emissions have been measured using a variety of technologies including ship-based (Riddick et al, 2019;Yacovitch et al, 2020;Zang et al, 2020), aircraft (Gorchov Negron et al, 2020;Foulds et al, 2022;Ayasse et al, 2022;Gorchov Negron et al, 2023), and satellite measurements (Lorente et al, 2022;Irakulis-Loitxate et al, 2022;Roger et al, 2023).…”

“…WorldView-3 and Landsat 8 measured offshore methane emissions from one platform in the Gulf of Mexico with an estimated source rate near 100,000 kg h −1 (Irakulis- Loitxate et al, 2022). The EnMap mission also used sun glint reflections to measure offshore methane emissions with source rates as low as 930 kg h −1 in the Gulf of Mexico (Roger et al, 2023). Having space-based remote sensing technologies that can approach the 100 kg h −1 detection limit offshore would allow for significantly more methane emissions to be monitored.…”