Point source detection and validation using GOSAT and OCO-2 data: Volcanoes and Power Plants

Abstract:

Point source emissions from power plants and non-erupting active volcanoes are continuous but variable in source strength and resulting plume direction. Power plant emission variations are driven by regular demand/load cycles, while volcanic CO₂ emissions follow less regular oscillations. Two polar orbiting sun-synchronous satellites currently measure atmospheric CO₂with sufficient sensitivity and spatial resolution to detect point sources and their plumes: GOSAT and OCO-2.

GOSAT, launched in January 2009 by JAXA, provides 260 km spaced single-sounding grid points at a 3-day repeat cycle with a circular field of view of 10km diameter, at ~0.25/s samples. OCO-2 (leading the A-train on the Calipso ground track, repeat cycle 16 days), launched in July 2014 by NASA continuously collects eight <3 km² cross-track elements at 24/s samples along a ~10 km wide swath either along-track (nadir), or in glint direction. GOSAT has an agile pointing system, permitting a large number of custom targets per orbit, at the expense of spatial context. OCO-2 provides up to 10,000 soundings over a different pre-programmed ~100 km²area each day. Consequently, observation strategies for point sources differ between the two missions. GOSAT can precisely and frequently and repeatedly target at the central emission point, providing a great opportunity for time series observations at its fast repeat cycle. In contrast, OCO-2 is targeting mainly validation sites (maximum 1 per orbit), thus maximizing spatial data continuity. However, close incidental flyby detection of plumes, with some along-swath spatial context, is possible with OCO-2.

Synergetic opportunities exist to aid in CO₂ plume identification, verification and validation. For OCO-2, other A-Train constellation satellites (e.g., OMI, MODIS, Calipso) provide independent parameters such as SO₂ and aerosol information. GOSAT TIR data can be used to retrieve SO₂values, providing plume validation, together with the GOSAT’s spatial aerosols data. GOSAT and OCO-2 offer synergies between each other through several near-coincident measurements per day, permitting direct cross-validation, as well as making use of the combination of incidental OCO-2 flybys at point sources and their plumes, and target mode time series from GOSAT.

© 2013 California Institute of Technology