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| Titel |
Spatial resolution of tropical terrestrial CO2 fluxes inferred using space-borne column CO2 sampled in different earth orbits: the role of spatial error correlations |
| VerfasserIn |
P. I. Palmer, L. Feng, H. Bösch |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 4, no. 9 ; Nr. 4, no. 9 (2011-09-23), S.1995-2006 |
| Datensatznummer |
250002103
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| Publikation (Nr.) |
 copernicus.org/amt-4-1995-2011.pdf |
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| Zusammenfassung |
| We use realistic numerical experiments to assess the sensitivity of
8-day CO2 flux estimates, inferred from space-borne short-wave
infrared measurements of column-averaged CO2 dry air mixing ratio
XCO2, 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 CO2 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 CO2 flux estimates on spatial scales
that approach those observed by regional aircraft. |
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