Abstract:
Satellite observations of atmospheric methane plumes offer a means for global mapping of methane point sources. This capability has so far been demonstrated only for anomalously large or regionally aggregated point sources. Here we use the GHGSat-D satellite instrument with 50-m spatial resolution and 9-19% single-pass column precision to quantify mean
source rates for three coal mine vents (San Juan, United States; Appin, Australia; Bulianta, China) under apparently normal operating conditions and over a 2-year period (2016-2018). This involves averaging wind-rotated observations from 13-24 overpasses to achieve satisfactory signal-to-noise. Our wind rotation method optimizes the wind direction information for individual plumes to account for error in meteorological databases. We derive source rates from the time-averaged plumes using integrated mass enhancement (IME) and cross-sectional flux (CSF) methods calibrated with large eddy simulations (LES). We find time-averaged source rates ranging from 2150 to 5690 kg h-1 for the three coal mine vents, with about 40% precision, and generally consistent with previous estimates, which are however highly variable. The IME and CSF methods agree within 15%. Our 2300 ± 1020 kg h-1 estimate for the San Juan mine is consistent with the annual mean value of 2585 kg h-1 for 2017 reported to the United States Greenhouse Gas Reporting Program (GHGRP). Our results demonstrate the potential of space-based monitoring for annual reporting of methane emissions from point sources, and suggest that future
satellite instruments with similar pixel resolution but better precision should be able to constrain a wide range of point sources.
