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| Titel |
Empirical analysis and modeling of errors of atmospheric profiles from GPS radio occultation |
| VerfasserIn |
B. Scherllin-Pirscher, A. K. Steiner, G. Kirchengast, Y.-H. Kuo, U. Foelsche |
| 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 (2011-09-13), S.1875-1890 |
| Datensatznummer |
250002095
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| Publikation (Nr.) |
 copernicus.org/amt-4-1875-2011.pdf |
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| Zusammenfassung |
| The utilization of radio occultation (RO) data in atmospheric studies
requires precise knowledge of error characteristics. We present results of
an empirical error analysis of GPS RO bending angle, refractivity, dry
pressure, dry geopotential height, and dry temperature. We find very good
agreement between data characteristics of different missions (CHAMP,
GRACE-A, and Formosat-3/COSMIC (F3C)).
In the global mean, observational errors (standard deviation from "true"
profiles at mean tangent point location) agree within 0.3% in bending
angle, 0.1% in refractivity, and 0.2 K in dry temperature at all
altitude levels between 4 km and 35 km.
Above 35 km the increase of the CHAMP raw bending angle observational
error is more pronounced than that of GRACE-A and F3C leading to a
larger observational error of about 1% at 42 km. Above ≈20 km,
the observational errors show a strong seasonal dependence at high
latitudes. Larger errors occur in hemispheric wintertime and are associated
mainly with background data used in the retrieval process particularly
under conditions when ionospheric residual is large. The comparison between
UCAR and WEGC results (both data centers have independent inversion
processing chains) reveals different magnitudes of observational errors in
atmospheric parameters, which are attributable to different background
fields used. Based on the empirical error estimates, we provide a simple
analytical error model for GPS RO atmospheric parameters for the altitude
range of 4 km to 35 km and up to 50 km for UCAR raw bending angle and
refractivity. In the model, which accounts for vertical, latitudinal, and
seasonal variations, a constant error is adopted around the tropopause
region amounting to 0.8% for bending angle, 0.35% for refractivity,
0.15% for dry pressure, 10 m for dry geopotential height, and 0.7 K
for dry temperature. Below this region the observational error increases
following an inverse height power-law and above it increases
exponentially.
For bending angle and refractivity we also include formulations for error
correlations in order to enable modeling of full error covariance matrices
for these primary data assimilation variables.
The observational error model is the same for UCAR and WEGC data but due to
somewhat different error characteristics below about 10 km and above about
20 km some parameters have to be adjusted. Overall, the observational
error model is easily applicable and adjustable to individual error
characteristics. |
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