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| Titel |
Optimization of the GSFC TROPOZ DIAL retrieval using synthetic lidar returns and ozonesondes – Part 1: Algorithm validation |
| VerfasserIn |
J. T. Sullivan, T. J. McGee, T. Leblanc, G. K. Sumnicht, L. W. Twigg |
| 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 ; 8, no. 10 ; Nr. 8, no. 10 (2015-10-09), S.4133-4143 |
| Datensatznummer |
250116629
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| Publikation (Nr.) |
 copernicus.org/amt-8-4133-2015.pdf |
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| Zusammenfassung |
The main purpose of the NASA Goddard Space Flight Center TROPospheric OZone
DIfferential Absorption Lidar (GSFC TROPOZ DIAL) is to measure the vertical
distribution of tropospheric ozone for science investigations. Because of the
important health and climate impacts of tropospheric ozone, it is imperative
to quantify background photochemical ozone concentrations and ozone layers
aloft, especially during air quality episodes. For these reasons, this paper
addresses the necessary procedures to validate the TROPOZ retrieval algorithm
and confirm that it is properly representing ozone concentrations. This paper
is focused on ensuring the TROPOZ algorithm is properly quantifying ozone
concentrations, and a following paper will focus on a systematic uncertainty
analysis.
This methodology begins by simulating synthetic lidar returns from actual
TROPOZ lidar return signals in combination with a known ozone profile. From
these synthetic signals, it is possible to explicitly determine retrieval
algorithm biases from the known profile. This was then systematically
performed to identify any areas that need refinement for a new operational
version of the TROPOZ retrieval algorithm. One immediate outcome of this
exercise was that a bin registration error in the correction for detector
saturation within the original retrieval was discovered and was subsequently
corrected for. Another noticeable outcome was that the vertical smoothing in
the retrieval algorithm was upgraded from a constant vertical resolution to a
variable vertical resolution to yield a statistical uncertainty of
<10 %. This new and optimized vertical-resolution scheme retains the
ability to resolve fluctuations in the known ozone profile, but it now allows
near-field signals to be more appropriately smoothed. With these revisions to
the previous TROPOZ retrieval, the optimized TROPOZ retrieval algorithm
(TROPOZopt) has been effective in retrieving nearly 200 m lower to
the surface. Also, as compared to the previous version of the retrieval, the
TROPOZopt had an overall mean improvement of 3.5 %, and large
improvements (upwards of 10–15 % as compared to the previous algorithm)
were apparent between 4.5 and 9 km. Finally, to ensure the
TROPOZopt retrieval algorithm is robust enough to handle actual
lidar return signals, a comparison is shown between four nearby ozonesonde
measurements. The ozonesondes are mostly within the TROPOZopt
retrieval uncertainty bars, which implies that this exercise was quite
successful. |
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