Ten years of MIPAS measurements with ESA Level 2 processor V6-Part 1: Retrieval algorithm and diagnostics of the products

Year: 2013

Authors: Raspollini P., Carli B., Carlotti M., Ceccherini S., Dehn A., Dinelli B.M., Dudhia A., Flaud J.M., Lopez-Puertas M., Niro F., Remedios J.J., Ridolfi M., Sembhi H., Sgheri L., Von Clarmann T.

Autors Affiliation: CNR, Ist Fis Applicata N Carrara IFAC, Florence, Italy
Univ Bologna, Bologna, Italy
CNR, ISAC, I-40126 Bologna, Italy
Univ Oxford, Clarendon Lab, Oxford OX1 2JD, England
Univ Paris 12, LISA, CNRS, F-94010 Creteil, France
Univ Paris 07, LISA, CNRS, F-75221 Paris 05, France
SERCO SpA, European Space Agcy ESA ESRIN, Frascati, Italy
CSIC, Inst Astrofis Andalucia, Granada, Spain
Univ Leicester, Dept Phys & Astron, Leicester LE1 7RH, Leics, England
CNR, IFAC, Sect Florence, Florence, Italy
Karlsruhe Inst Technol, Inst Meteorol & Climate Res IMK, D-76021 Karlsruhe, Germany
ESA ESRIN, Frascati, Italy

Abstract: 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, O-3, 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.

Journal/Review: ATMOSPHERIC MEASUREMENT TECHNIQUES

Volume: 6 (9)      Pages from: 2419  to: 2439

More Information: This work has been performed under the ESA study “Support to MIPAS Level 2 product validation”, contract ESA-ESRIN no. 21719/08/I-OL. The authors are grateful to the Astrium team that developed the industrial prototype ML2PP using the ORM code as reference, to Thorsten Fehr and Rolf von Kulhmann for the coordination of the MIPAS Quality Working Group activities and to Michael Kiefer for the work done within the MIPAS Quality Working Group.
KeyWords: ALTITUDE-DEPENDENT REGULARIZATION; ATMOSPHERIC SOUNDING MIPAS; MICHELSON INTERFEROMETER; GEOPHYSICAL VALIDATION; DATA ASSIMILATION; UPPER TROPOSPHERE; TECHNICAL NOTE; TEMPERATURE; ENVISAT; RESOLUTION
DOI: 10.5194/amt-6-2419-2013

Citations: 52
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