Coordinated satellite, aircraft, and ground-based observations of a large transient methane release.

We present the results of a Very Large Methane Release (VLMR) experiment evaluating methane retrievals from the Geostationary Operational Environmental Satellites (GOES) Advanced Baseline Imagers (ABIs) and multiple low-Earth-orbit satellite instruments with high point-source detection thresholds. The experiment coordinated observations of a US gas pipeline blowdown with nine satellites, an aircraft, and a truck-based mobile laboratory. We used the GOES-16, -18, and -19 ABIs with revisits every 10 min to 7 s to quantify release magnitude and associated uncertainty. Best methane retrieval precision of 7% was achieved in the 30-s mesoscale scan modes averaged to 5 min, yielding an estimated methane plume detection threshold of 15 to 30 t h-1 per m s-1 of wind. GOES detected total emissions of 370 ± 30 t over 42 to 63 min from two release points. Source rate and mass estimates are broadly consistent across measurement platforms, but the total detected release mass is ~25% lower than that reported by the operator based on pipeline volume and pressure. This discrepancy may reflect late-stage emissions below satellite detection thresholds and indicates a potential low bias in satellite estimates of total emissions from large transient releases. Coordinated field experiments such as VLMR can complement existing controlled-release satellite evaluation programs by providing a framework to validate observations of very large methane point sources.