Satellite observations of atmospheric methane and their value for quantifying methane emissions

Abstract

Abstract. Methane is a greenhouse gas emitted by a range of natural and anthropogenic sources. Atmospheric methane has been measured continuously from space since 2003, and new instruments are planned for launch in the near future that will greatly expand the capabilities of space-based observations. We review the value of current, future, and proposed satellite observations to better quantify and understand methane emissions through inverse analyses, from the global scale down to the scale of point sources and in combination with suborbital (surface and aircraft) data. Current global observations from Greenhouse Gases Observing Satellite (GOSAT) are of high quality but have sparse spatial coverage. They can quantify methane emissions on a regional scale (100-1000 km) through multiyear averaging. The Tropospheric Monitoring Instrument (TROPOMI), to be launched in 2017, is expected to quantify daily emissions on the regional scale and will also effectively detect large point sources. A different observing strategy by GHGSat (launched in June 2016) is to target limited viewing domains with very fine pixel resolution in order to detect a wide range of methane point sources. Geostationary observation of methane, still in the proposal stage, will have the unique capability of mapping source regions with high resolution, detecting transient "super-emitter" point sources and resolving diurnal variation of emissions from sources such as wetlands and manure. Exploiting these rapidly expanding satellite measurement capabilities to quantify methane emissions requires a parallel effort to construct high-quality spatially and sectorally resolved emission inventories. Partnership between top-down inverse analyses of atmospheric data and bottom-up construction of emission inventories is crucial to better understanding methane emission processes and subsequently informing climate policy.

Constraining sector-specific CO<sub>2</sub> and CH<sub>4</sub> emissions in the US

“…Streets et al (2013) describe a number of these satellites in detail, and Jacob et al (2016) provide a thorough overview of CH 4 -observing satellites. Several of these satellites (Envisat/SCIAMACHY, GOSAT, OCO-2, and GHGSat) observe in the shortwave infrared.…”

“…A year of observations should be sufficient to detect the largest 1 % of grid cells in the EPA's gridded CH 4 inventory , equivalent to 30 % of total national emissions . Jacob et al (2016) define emissions as detectable if the total column CH 4 enhancement is more than twice the sensor precision at aggregated timescales.…”

Retrieval and validation of MetOp/IASI methane

“…TIR instruments measure the thermal radiation emitted by the Earth and the atmosphere, and operate in a nadir, limb or solar occultation observing mode. Limb and solar occultation detect CH 4 vertical profiles in the stratosphere and upper troposphere (Jacob et al, 2016). TIR nadir measurements provide integrated CH 4 columns in the middle to upper troposphere and register day and nighttime concentrations, over land and sea.…”

“…Jacob et al (2016) give an extensive overview of past and future satellite missions dedicated to detect methane. Atmospheric CH 4 is detectable by its absorption of radiation in the shortwave infrared (SWIR) and thermal infrared (TIR).…”

“…Atmospheric CH 4 is detectable by its absorption of radiation in the shortwave infrared (SWIR) and thermal infrared (TIR). SWIR instruments, such as SCIA-MACHY (Frankenberg et al, 2006), TANSO-FTS (Kuze et al, 2016) and the recently launched TROPOMI instrument (Hu et al, 2016), measure the solar radiation backscattered by the Earth and the atmosphere, and give a total atmospheric column of CH 4 with near uniform sensitivity in the troposphere (Jacob et al, 2016). TIR instruments measure the thermal radiation emitted by the Earth and the atmosphere, and operate in a nadir, limb or solar occultation observing mode.…”