 |
| Titel |
GOSAT Measurements of CO2 and CH4 Columns: Impact of Reduced Spectral Resolution on Retrieval Accuracy |
| VerfasserIn |
André Galli, Jochen Landgraf, Sandrine Guerlet, André Butz, Hiroshi Suto, Nicholas M. Deutscher, Justus Notholt, Debra Wunch, David W. T. Griffith, Otto Hasekamp, Ilse Aben |
| Konferenz |
EGU General Assembly 2013
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250075217
|
|
|
|
|
|
| Zusammenfassung |
| The Carbon Monitoring Satellite (CarbonSat) is one of two candidate Earth Explorer
Opportunity Missions, scheduled for launch in 2018. Its goal is to monitor tropospheric CO2
and CH4 by measuring reflected Sun light in the infrared (four separate observation
windows between 0.7 and 2.0 μm). Since the Fourier-transform spectrometer on
board the Japanese GOSAT satellite observes at a very similar range as the planned
CarbonSat spectrometer, GOSAT spectra offer an excellent opportunity to study the
impact of instrument settings on retrieval accuracy. The main topic of this study is
the impact of spectral resolution on retrieval accuracy of CO2 and CH4, i.e., does
a lowered resolution make spectroscopic errors more obvious? This question is
relevant for the CarbonSat mission because the instrument line shape will probably be
about five times broader than for GOSAT, but it is also of general interest for the
remote sensing of CO2 and CH4. Two different approaches are used to reduce the
spectral resolution of the native GOSAT spectra. The columns of CO2 and CH4 that
are retrieved from the spectra are then compared to collocated observations from
six different observation sites of the Total Carbon Column Observing Network
(TCCON).
The two instrument settings with a similar spectral resolution but different degradation
approach give a similar increase in scatter and decrease of correlation. For the CO2 retrieval
accuracy, the only notable effect of lowering the spectral resolution from GOSAT to
CarbonSat resolution is the increase of the standard deviation of retrieval errors from 0.7% to
1.0%. Other quality criteria (convergence, inter-stational bias) do not change. For CH4
columns, the standard deviation hardly increases (from 0.9% to 1.0%). Reducing the spectral
resolution does not further increase the strength nor the significance of retrieval biases with
respect to water abundance, albedo, or solar zenith angle. The selective degradation of single
windows demonstrates that the retrieval accuracy of CO2 and CH4 is dominated by
the spectral range where the absorption bands of the target molecule are situated. |
|
|
|
|
|
|