Level 2 processor and auxiliary data for ESA Version 8 final full mission analysis of MIPAS measurements on ENVISAT

Abstract

Abstract. High quality long-term data sets of altitude-resolved measurements of the atmospheric composition are important because they can be used both to study the evolution of the atmosphere and as a benchmark for future missions. For the final ESA reprocessing of MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) on ENVISAT (ENViromental SATellite) data, numerous improvements were implemented in the Level 2 (L2) processor Optimised Retrieval Model (ORM) version 8.22 (V8) and its auxiliary data. The implemented changes involve all aspects of the processing chain, from the modelling of the measurements with the handling of the horizontal inhomogeneities along the line of sight to the use of the optimal estimation technique to retrieve the minor species, from a more sensitive approach to detecting the spectra affected by clouds to a refined method for identifying low quality products. Improvements in the modelling of the measurements were also obtained with an update of the used spectroscopic data and of the databases providing the a priori knowledge of the atmosphere. The HITRAN_mipas_pf4.45 spectroscopic database was finalised with new spectroscopic data verified with MIPAS measurements themselves, while recently measured cross-sections were used for the heavy molecules. The Level 2 Initial Guess (IG2) data set, containing the climatology used by the MIPAS L2 processor to generate the initial guess and interfering species profiles when the retrieved profiles from previous scans are not available, was improved taking into account the diurnal variation of the profiles defined using climatologies from both measurements and models. Horizontal gradients were generated using the ECMWF ERA-Interim data closest in time and space to the MIPAS data. Further improvements in the L2 V8 products derived from the use of the L1b V8 products, which were upgraded to reduce the instrumental temporal drift and to handle the abrupt changes in the calibration gain. The improvements introduced into the ORM V8 L2 processor and its upgraded auxiliary data, together with the use of the L1b V8 products, lead to the generation of the MIPAS L2 V8 products, which are characterised by an increased accuracy, better temporal stability and a greater number of retrieved species.

Long-term validation of MIPAS ESA operational products using MIPAS-B measurements

“…In the following subsections, we discuss the validation of all quantities delivered operationally by ESA's L1v8 and L2v8 FM processor on the basis of collocated MIPAS-B observations. Only MIPAS satellite data that have passed the a posteriori quality check (mainly retrieval convergence and size of maximum error; for details, see Raspollini et al, 2022) were used for the intercomparison. The analysis of all compared vertical profiles is regarded as the evaluation with the highest statistical evidence.…”

“…The ESA L1v8/L2v8 diagnostic dataset (DDS) version was released in June 2018 followed by the L1v8 and L2v8 full mission (FM) data in June 2019. The new v8 data release (ESA, 2021b;Dinelli et al, 2021;Raspollini et al, 2022) comprises the additional molecules C 2 H 2 , C 2 H 6 , COCl 2 , OCS, CH 3 Cl, and HDO. For the final ESA reprocessing of MIPAS-E data, numerous improvements were implemented in the L2 processor optimised retrieval model (ORM) version 8.22 (v8) and its auxiliary data, including an update of the spectroscopic data used (Raspollini et al, 2022).…”

“…The new v8 data release (ESA, 2021b;Dinelli et al, 2021;Raspollini et al, 2022) comprises the additional molecules C 2 H 2 , C 2 H 6 , COCl 2 , OCS, CH 3 Cl, and HDO. For the final ESA reprocessing of MIPAS-E data, numerous improvements were implemented in the L2 processor optimised retrieval model (ORM) version 8.22 (v8) and its auxiliary data, including an update of the spectroscopic data used (Raspollini et al, 2022). An exemplary overview on the spectral regions used for the operational retrievals, together with typical errors (winter, OR mode), is given in Table 1.…”

“…Different spectral microwindows within mostly the same molecular bands were used for the MIPAS-E data analysis (Dinelli et al, 2021). Spectroscopic parameters for the calculation of the infrared emission spectra originate from the high-resolution transmission (HITRAN) molecular absorption database (Rothman et al, 2009) and a MIPAS-E dedicated spectroscopic database (Raspollini et al, 2022). For heavy molecules like CFC-11, CFC-12, HCFC-22, CCl 4 , and CF 4 , new and improved infrared absorption cross sections (Harrison, 2015(Harrison, , 2016Harrison et al, 2017) were used for the calculation of radiative transfer (consistent with the MIPAS-E retrieval).…”

IMK/IAA MIPAS retrievals version 8: CH4 and N2O

“…While the ESA provides their own data product (Dinelli et al, 2021;Raspollini et al, 2022), in this paper recent improvements of the retrieval of CH 4 and N 2 O from MIPAS radiance spectra version 8.03 with the level-2 data processor developed and operated by the Institute for Meteorology and Climate Research (IMK) in cooperation with the Instituto de Astrofísica de Andalucía (IAA) are discussed. Improvements with respect to calibration of the version 8.03 radiance spectra and their relevance to the retrieval are discussed in Kiefer et al (2021) and Kiefer et al (2022). Here we concentrate on the progress made with respect to level-2 processing, i.e., the inference of volume mixing ratios (VMR) from the radiance spectra and related data characterization.…”