An Independent Evaluation of GHGSat Methane Emissions: Performance Assessment.

An independent evaluation of methane emissions data from GHGSat, a private company that operates a constellation of small microsatellites flying Fabry‐Perot spectrometers operating at 1.6 µm, was performed. Data from multiple GHGSat commercial satellites, consisting of retrieved methane, diagnostics, and, where detected, plume and emissions information from roughly 250 scenes across Canada were analyzed. From these, 10 scenes contained methane plumes with a 2% detection rate for oil and gas scenes, and 10% for landfills. Methane precision was found to be 5%/2% on average for the C1/C2–C5 designs, with some variability due to scene albedo, terrain roughness, and airmass. Synthetic GHGSat plumes, generated using Lagrangian plume dispersion model and GHGSat characteristics, indicates typical detection limits of 240/180 kg/hr(C1/C2–C5), with a best case of roughly 100 kg/hr. Emissions and their uncertainties calculated using an alternative approach were in broad agreement with GHGSat‐reported emissions. Overall, the performance of the GHGSat C2 design (also used for C3 onward) for favorable‐viewing conditions was found to be largely consistent with company‐advertised performance. Plain Language Summary: We performed an independent evaluation of methane emissions data from GHGSat, a private company that owns and operates its own group of satellites, in order to evaluate the precision of their methane data products and compare these findings with that advertised. Roughly 250 GHGSat data scenes were acquired with 10 plumes detected, 2 for oil and gas and 8 for landfills. These, combined with advanced plume models, statistical analyses, and alternative data processing software, were used in the evaluation. It was found that the GHGSat‐reported detection limit—the quantity of methane release that was is the edge of detectability—of 100 kg/hr was possible, but only for ideal conditions. Ideal in this case means a surface that is quite reflective (at the wavelengths detected by the GHGSat sensors, roughly 1.6 μm) and flat near the source of the emissions. A detection limit of 180 kg/hr is more representative of average conditions. Key Points: GHGSat methane precision was found to be 1%–5%, varying with surface reflectance, terrain variability, and solar zenith angleGHGSat methane detection limit can be as low as 100 kg/hr under ideal conditions, but more typically is about 200 kg/hrGHGSat performance was found to be generally consistent with that reported by the company [ABSTRACT FROM AUTHOR]