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| Titel |
Greenhouse gas profiling by infrared-laser and microwave occultation: retrieval algorithm and demonstration results from end-to-end simulations |
| VerfasserIn |
V. Proschek, G. Kirchengast, S. Schweitzer |
| 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. 10 ; Nr. 4, no. 10 (2011-10-04), S.2035-2058 |
| Datensatznummer |
250002106
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| Publikation (Nr.) |
 copernicus.org/amt-4-2035-2011.pdf |
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| Zusammenfassung |
| Measuring greenhouse gas (GHG) profiles with global coverage and high
accuracy and vertical resolution in the upper troposphere and lower
stratosphere (UTLS) is key for improved monitoring of GHG concentrations
in the free atmosphere. In this respect a new satellite mission concept
adding an infrared-laser part to the already well studied microwave
occultation technique exploits the joint propagation of infrared-laser
and microwave signals between Low Earth Orbit (LEO) satellites. This
synergetic combination, referred to as LEO-LEO microwave and
infrared-laser occultation (LMIO) method, enables to retrieve
thermodynamic profiles (pressure, temperature, humidity) and accurate
altitude levels from the microwave signals and GHG profiles from the
simultaneously measured infrared-laser signals. However, due to the
novelty of the LMIO method, a retrieval algorithm for GHG profiling is
not yet available. Here we introduce such an algorithm for retrieving
GHGs from LEO-LEO infrared-laser occultation (LIO) data, applied as a
second step after retrieving thermodynamic profiles from LEO-LEO
microwave occultation (LMO) data. We thoroughly describe the LIO
retrieval algorithm and unveil the synergy with the LMO-retrieved
pressure, temperature, and altitude information. We furthermore
demonstrate the effective independence of the GHG retrieval results from
background (a priori) information in discussing demonstration results
from LMIO end-to-end simulations for a representative set of GHG
profiles, including carbon dioxide (CO2), water vapor (H2O),
methane (CH4), and ozone (O3). The GHGs except for ozone are
well retrieved throughout the UTLS, while ozone is well retrieved from
about 10 km to 15 km upwards, since the ozone layer resides in the
lower stratosphere. The GHG retrieval errors are generally smaller than
1% to 3% r.m.s., at a vertical resolution of about 1 km. The
retrieved profiles also appear unbiased, which points to the climate
benchmarking capability of the LMIO method. This performance, found here
for clear-air atmospheric conditions, is unprecedented for vertical
profiling of GHGs in the free atmosphere and encouraging for future LMIO
implementation. Subsequent work will examine GHG retrievals in cloudy
air, addressing retrieval performance when scanning through intermittent
upper tropospheric cloudiness. |
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