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| Titel |
Atmospheric influences on infrared-laser signals used for occultation measurements between Low Earth Orbit satellites |
| VerfasserIn |
S. Schweitzer, G. Kirchengast, V. Proschek |
| 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 (2011-10-21), S.2273-2292 |
| Datensatznummer |
250002123
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| Publikation (Nr.) |
 copernicus.org/amt-4-2273-2011.pdf |
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| Zusammenfassung |
| LEO-LEO infrared-laser occultation (LIO) is a new occultation technique between
Low Earth Orbit (LEO) satellites, which applies signals in the short wave
infrared spectral range (SWIR) within 2 μm to 2.5 μm. It is part
of the LEO-LEO microwave and infrared-laser occultation (LMIO) method
that enables to retrieve
thermodynamic profiles (pressure, temperature, humidity) and
altitude levels from microwave signals and profiles of greenhouse
gases and further variables such as line-of-sight wind speed from simultaneously measured
LIO signals.
Due to the novelty of the LMIO method, detailed knowledge of atmospheric
influences on LIO signals and of their suitability for accurate
trace species retrieval did not yet exist. Here we discuss these influences,
assessing effects from refraction, trace species absorption, aerosol extinction
and Rayleigh scattering in detail, and addressing clouds, turbulence, wind,
scattered solar radiation and terrestrial thermal radiation as well.
We show that the influence of refractive defocusing, foreign species absorption,
aerosols and turbulence is observable, but can be rendered small to
negligible by use of the differential transmission principle
with a close frequency spacing of LIO absorption and reference
signals within 0.5%. The influences of Rayleigh scattering
and terrestrial thermal radiation
are found negligible. Cloud-scattered solar radiation can be observable under
bright-day conditions, but this influence can be
made negligible by
a close time spacing (within 5 ms)
of interleaved laser-pulse and background signals. Cloud extinction
loss generally blocks SWIR signals, except very thin or
sub-visible cirrus clouds, which can be addressed by
retrieving a cloud layering profile and exploiting it in the trace
species retrieval.
Wind can have a small influence
on the trace species absorption,
which can be made negligible by
using a simultaneously retrieved or a moderately accurate
background wind speed profile.
We conclude that the set of
SWIR channels proposed for implementing the LMIO method
(Kirchengast and Schweitzer, 2011) provides
adequate sensitivity to accurately retrieve eight
trace species of key importance to climate and atmospheric chemistry
(H2O, CO2, 13CO2, C18OO, CH4, N2O,
O3, CO) in the upper troposphere/lower stratosphere region outside
clouds under all atmospheric conditions. Two further
species (HDO, H218O) can be retrieved in the upper troposphere. |
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