Assessing the capability of different satellite observing configurations to resolve the distribution of methane emissions at kilometer scales

Abstract

Anthropogenic methane emissions originate from a large number of fine-scale and often transient point sources. Satellite observations of atmospheric methane columns are an attractive approach for monitoring these emissions but have limitations from instrument precision, pixel resolution, and measurement frequency. Dense observations will soon be available in both low-Earth and geostationary orbits, but the extent to which they can provide fine-scale information on methane sources has yet to be explored. Here we present an observation system simulation experiment (OSSE) to assess the capabilities of different satellite observing system configurations. We conduct a 1-week WRF-STILT simulation to generate methane column footprints at 1.3ĝ€ × ĝ€1.3ĝ€km2 spatial resolution and hourly temporal resolution over a 290ĝ€ × ĝ€235ĝ€km2 domain in the Barnett Shale, a major oil and gas field in Texas with a large number of point sources. We sub-sample these footprints to match the observing characteristics of the recently launched TROPOMI instrument (7ĝ€ × ĝ€7ĝ€km2ĝ€pixels, 11ĝ€ppb precision, daily frequency), the planned GeoCARB instrument (2.7ĝ€ × ĝ€3.0ĝ€km2ĝ€pixels, 4ĝ€ppb precision, nominal twice-daily frequency), and other proposed observing configurations. The information content of the various observing systems is evaluated using the Fisher information matrix and its eigenvalues. We find that a week of TROPOMI observations should provide information on temporally invariant emissions at ĝ1/4 ĝ€30ĝ€kmĝ€spatial resolution. GeoCARB should provide information available on temporally invariant emissions ĝ1/4 ĝ€2-7ĝ€km spatial resolution depending on sampling frequency (hourly to daily). Improvements to the instrument precision yield greater increases in information content than improved sampling frequency. A precision better than 6ĝ€ppb is critical for GeoCARB to achieve fine resolution of emissions. Transient emissions would be missed with either TROPOMI or GeoCARB. An aspirational high-resolution geostationary instrument with 1.3ĝ€ × ĝ€1.3ĝ€km2ĝ€pixel resolution, hourly return time, and 1ĝ€ppb precision would effectively constrain the temporally invariant emissions in the Barnett Shale at the kilometer scale and provide some information on hourly variability of sources.