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| Titel |
Ten years of MIPAS measurements with ESA Level 2 processor V6 – Part 1: Retrieval algorithm and diagnostics of the products |
| VerfasserIn |
P. Raspollini, B. Carli, M. Carlotti, S. Ceccherini, A. Dehn, B. M. Dinelli, A. Dudhia, J.-M. Flaud, M. López-Puertas, F. Niro, J. J. Remedios, M. Ridolfi, H. Sembhi, L. Sgheri, T. Clarmann |
| 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 ; 6, no. 9 ; Nr. 6, no. 9 (2013-09-23), S.2419-2439 |
| Datensatznummer |
250085066
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| Publikation (Nr.) |
 copernicus.org/amt-6-2419-2013.pdf |
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| Zusammenfassung |
The MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) instrument on the Envisat (Environmental satellite) satellite has provided vertical
profiles of the atmospheric composition on a global scale for almost
ten years. The MIPAS mission is divided in two phases: the full
resolution phase, from 2002 to 2004, and the optimized resolution
phase, from 2005 to 2012, which is characterized by a finer vertical
and horizontal sampling attained through a reduction of the spectral
resolution.
While the description and characterization of the products of the
ESA processor for the full resolution phase has been already
described in previous papers, in this paper we focus on the
performances of the latest version of the ESA (European Space Agency) processor, named ML2PP
V6 (MIPAS Level 2 Prototype Processor), which has been used for reprocessing the entire mission. The ESA
processor had to perform the operational near real time analysis of
the observations and its products needed to be available for data
assimilation. Therefore, it has been designed for fast, continuous
and automated analysis of observations made in quite different
atmospheric conditions and for a minimum use of external constraints
in order to avoid biases in the products.
The dense vertical sampling of the measurements adopted in the
second phase of the MIPAS mission resulted in sampling intervals
finer than the instantaneous field of view of the instrument.
Together with the choice of a retrieval grid aligned with the
vertical sampling of the measurements, this made ill-conditioned the
retrieval problem of the MIPAS operational processor. This problem
has been handled with minimal changes to the original retrieval
approach but with significant improvements nonetheless. The
Levenberg–Marquardt method, already present in the retrieval scheme
for its capability to provide fast convergence for nonlinear
problems, is now also exploited for the reduction of the
ill-conditioning of the inversion. An expression specifically
designed for the regularizing Levenberg–Marquardt method has been
implemented for the computation of the covariance matrices and
averaging kernels of the retrieved products. The regularization of
the Levenberg–Marquardt method is controlled by the convergence
criteria and is deliberately kept weak. The resulting oscillations
of the retrieved profile are a posteriori damped by an innovative
self-adapting Tikhonov regularization. The convergence criteria and
the weakness of the self-adapting regularization ensure that minimum
constraints are used and the best vertical resolution obtainable
from the measurements is achieved in all atmospheric conditions.
Random and systematic errors, as well as vertical and horizontal
resolution are compared in the two phases of the mission for all
products, namely: temperature, H2O, O3,
HNO3, CH4, N2O, NO2, CFC-11, CFC-12,
N2O5 and ClONO2. The use in the two phases of the
mission of different optimized sets of spectral intervals ensures
that, despite the different spectral resolutions, comparable
performances are obtained in the whole MIPAS mission in terms of
random and systematic errors, while the vertical resolution and the
horizontal resolution are significantly better in the case of the
optimized resolution measurements. |
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