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| Titel |
Inversion and space-time-averaging algorithms for ScaRaB (Scanner for the Earth Radiation Budget). Comparison with ERBE |
| VerfasserIn |
M. Viollier, R. Kandel, P. Raberanto |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 13, no. 9 ; Nr. 13, no. 9, S.959-968 |
| Datensatznummer |
250011981
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| Publikation (Nr.) |
 copernicus.org/angeo-13-959-1995.pdf |
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| Zusammenfassung |
| Establishment of a uniform long-term record
of "top-of-the atmosphere" (TOA) Earth radiation budget (ERB)
components, on a scale appropriate to the study of cloud radiation interactions,
requires that the data obtained from different observation missions satisfy two
basic conditions: (1) the broadband shortwave (SW:0.2–4 µm) and longwave (LW:
4–50 µm) radiances must be demonstrably made on the same absolute scale; and
(2) the methods used first to convert the instantaneous (filtered) radiances
into (unfiltered) SW and LW radiant fluxes, and then to perform the space-time
integrations to yield regional monthly means, must be consistent. Here we
consider mainly the second point, with regard to the ScaRaB/Meteor mission in
orbit since 25 January 1994 and observing the Earth since 24 February 1994. The
objective of this mission is to determine the TOA ERB components and so to
provide a continuation of the NASA ERBE scanner mission (November 1984–February
1990). We show how results compatible with ERBE can be obtained by taking into
account the instrumental characteristics and the satellite orbit parameters:
spectral response of the broadband channels, Earth local time of observation.
Considering the spectral response of the ScaRaB broadband channels, we show that
no spectral correction is required in the longwave domain, whereas a correction
of +4.5% must be applied in the shortwave domain for clear and partly cloudy
ocean, in order to compensate for underestimation at the shortest wavelengths.
Despite possible differences between ERBE and ScaRaB procedures in values
assumed for certain parameters of the scene/cloud identifications, application
of these procedures to the same set of ERBE data (spectrally corrected, i.e.
"unfiltered" radiances) shows that scene identification agreement is
close to 90% and that, where there is disagreement, resulting differences in LW
fluxes are negligible, those in SW fluxes small. We show that regional and
global mean quantities are in excellent agreement, considering that differences
between (ERBS+NOAA-9) and (NOAA-9 only) results may be taken as illustrating
time-sampling effects. We find that biases may occur from the undersampling,
specifically for the night-time clear-sky estimation over land and desert.
Preliminary results using ScaaB data of March 1994 show that clear-sky regional
estimates may be less numerous than in ERBE scanner products, due to either the
larger pixel size or the auxiliary parameters used in the scene identification,
and that expected uncertainties in the global monthly mean values depend
mainly on the instrument radiometric calibration. |
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