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| Titel |
PPDF-based retrievals of atmospheric methane from GOSAT observations |
| VerfasserIn |
A. Bril, S. Oshchepkov, I. Morino, O. Uchino, D. Belikov, H.-S. Kim, S. Maksyutov, T. Yokota |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250061791
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| Zusammenfassung |
| We present over-globe retrievals of atmospheric methane column-averaged abundance
(XCH4) obtained with PPDF (Photon path-length Probability Density Function)-based
algorithm from observations by Greenhouse gases Observing SATellite (GOSAT)
for 22 months from June 2009. The algorithm retrieves both target gas amount
and PPDF-parameters that are responsible for the optical path modification due to
atmospheric light scattering. PPDF parameters were estimated by using the oxygen
A-band data. The GOSAT scans with PPDF-parameters below an empirically chosen
threshold were considered as “clear-sky” (i.e. with negligible optical path modification).
These scans were used for methane retrievals from 1.67 μm absorption band at
zero PPDF parameters. The retrieval state vector included vertical profile of the
methane mixing ratio; scaling factor of prior water vapor profile; and stretch factor
for adjusting the position of the wave-number grids. Meteorological temperature
profiles and surface pressure data (GVP) were provided by Japan Meteorological
Agency.
We focus on the comparison of the satellite-based methane retrievals with those available
from TCCON (Total Carbon Column Observing Network) measurements. We found latitude
dependent variations of PPDF versus TCCON XCH4 bias (up to 15 ppb) which are
comparable with estimated GOSAT single scan precision. Comparison of the retrievals with
transport model (NIES-TM) data revealed good agreement for GOSAT over-land
observations and stable negative bias (0.3 – 0.8 %) of PPDF versus NIES-TM XCH4 for
over-sea observations. |
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