 |
| Titel |
Inversion, error analysis, and validation of GPS/MET occultation data |
| VerfasserIn |
A. K. Steiner, G. Kirchengast, H. P. Ladreiter |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 17, no. 1 ; Nr. 17, no. 1, S.122-138 |
| Datensatznummer |
250013650
|
| Publikation (Nr.) |
 copernicus.org/angeo-17-122-1999.pdf |
|
|
|
|
|
| Zusammenfassung |
The global positioning system meteorology
(GPS/MET) experiment was the first practical demonstration of global navigation
satellite system (GNSS)-based active limb sounding employing the radio
occultation technique. This method measures, as principal observable and with
millimetric accuracy, the excess phase path (relative to propagation in vacuum)
of GNSS-transmitted radio waves caused by refraction during passage through the
Earth's neutral atmosphere and ionosphere in limb geometry. It shows great
potential utility for weather and climate system studies in providing an unique
combination of global coverage, high vertical resolution and accuracy, long-term
stability, and all-weather capability. We first describe our GPS/MET data
processing scheme from excess phases via bending angles to the neutral
atmospheric parameters refractivity, density, pressure and temperature. Special
emphasis is given to ionospheric correction methodology and the inversion of
bending angles to refractivities, where we introduce a matrix inversion
technique (instead of the usual integral inversion). The matrix technique is
shown to lead to identical results as integral inversion but is more directly
extendable to inversion by optimal estimation. The quality of GPS/MET-derived
profiles is analyzed with an error estimation analysis employing a Monte Carlo
technique. We consider statistical errors together with systematic errors due to
upper-boundary initialization of the retrieval by a priori bending angles.
Perfect initialization and properly smoothed statistical errors allow for better
than 1 K temperature retrieval accuracy up to the stratopause. No initialization
and statistical errors yield better than 1 K accuracy up to 30 km but less than
3 K accuracy above 40 km. Given imperfect initialization, biases >2 K
propagate down to below 30 km height in unfavorable realistic cases.
Furthermore, results of a statistical validation of GPS/MET profiles through
comparison with atmospheric analyses of the European Centre for Medium-range
Weather Forecasts (ECMWF) are presented. The comparisons indicate the high
utility of the occultation data in that very good agreement of upper
troposphere/lower stratosphere temperature (better than 1.5 K rms, <0.5 K
bias) is found for a region (Europe+USA) where the ECMWF analyses are known to
be good, but poorer agreement for a region (Southern Pacific) where the analyses
are known to be degraded.
Key words. Atmospheric composition and structure
(pressure; density and temperature), Meteorology and atmospheric dynamics
(instruments and techniques), Radio science (remote sensing) |
| |
|
| Teil von |
|
|
|
|
|
|
|
|