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Title: Spatial resolution of tropical terrestrial CO[subscript 2] fluxes inferred using space-borne column CO[subscript 2] sampled in different earth orbits: the role of spatial error correlations
Authors: Palmer, P.I.
Feng, L.
Bösch, H.
First Published: 2011
Publisher: Copernicus GmbH (Copernicus Publications) on behalf of the European Geosciences Union (EGU)
Citation: Atmospheric Measurement Techniques, 2011, 4 (9), pp. 1995-2006
Abstract: We use realistic numerical experiments to assess the sensitivity of 8-day CO[subscript 2] flux estimates, inferred from space-borne short-wave infrared measurements of column-averaged CO[subscript 2] dry air mixing ratio X[subscript CO2], to the choice of Earth observing orbit. We focus on three orbits: (1) a low-inclination circular orbit used by the NASA Tropical Rainfall Measuring Mission (TRMM); (2) a sun-synchronous orbit used by the Japanese Greenhouse Gases Observing SATellite (GOSAT) and proposed for the NASA Orbiting Carbon Observatory (OCO-2) instrument; and (3) a precessing orbit used by the International Space Station (ISS). For each orbit, we assume an instrument based on the specification of the OCO-2; for GOSAT we use the relevant instrument specification. Sun-synchronous orbits offer near global coverage within a few days but have implications for the density of clear-sky measurements. The TRMM and ISS orbits intensively sample tropical latitudes, with sun-lit clear-sky measurements evenly distributed between a.m./p.m. For a specified spatial resolution for inferred fluxes, we show there is a critical number of measurements beyond which there is a disproportionately small decrease in flux uncertainty. We also show that including spatial correlations for measurements and model errors (of length 300 km) reduces the effectiveness of high measurement density for flux estimation, as expected, and so should be considered when deciding sampling strategies. We show that cloud-free data from the TRMM orbit generally can improve the spatial resolution of CO[subscript 2] fluxes achieved by OCO-2 over tropical South America, for example, from 950 km to 630 km, and that combining data from these low-inclination and sun-synchronous orbits have the potential to reduce this spatial length further. Decreasing the length of the error correlations to 50 km, reflecting anticipated future improvements to transport models, results in CO[subscript 2] flux estimates on spatial scales that approach those observed by regional aircraft.
DOI Link: 10.5194/amt-4-1995-2011
ISSN: 1867-1381
eISSN: 1867-8548
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2011 The authors. This is an open-access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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