Marco Ridolfi

MIPAS ground processor and data products

As an ESA-provided payload instrument on board ENVISAT the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) will routinely acquire atmospheric limb emission spectra in the middle infrared region. Due to its high radiometric sensitivity and spectral resolution capabilities a large number of middle atmospheric constituents can be detected that are of primary interest in the various disciplines of atmospheric research. The ENVISAT ground segment concept foresees generation and near real time dissemination of MIPAS data products up to the level of pressure (p), temperature (T) and volume-mixing-ratio (VMR) profiles for the high priority target species O/sub 3/, H/sub 2/O, CH/sub 4/, N/sub 2/O, HNO/sub 3/. The basic algorithms have been defined and are currently being verified in various ESA supported studies. End-to-end tests based on simulated instrument raw data have been carried out, using prototype versions of the Level 1B (processing from raw data up to calibrated radiance spectra) and Level 2 algorithm components (retrieval of vertical p, T and VMR profiles). Runtime checks have been performed for the critical profile retrieval modules. For a reference scenario (p, T plus five trace gas retrievals for a single, 16 heights elevation sequence; one iteration per retrieval), a total runtime of /spl sim/150 s has been achieved on an IBM RS/6000 model 397.

Level 2 near-real-time analysis of MIPAS measurements on ENVISAT

MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) is operating on board of the ENVISAT satellite and is acquiring for the first time high spectral resolution middle infrared emission limb sounding spectra of the Earth atmosphere from space. The measurement capabilities make it possible to determine every 75 sec. the vertical profile of several atmospheric trace constituents, during both day and night with an almost full coverage of the globe. This leads to a three dimensional measurement of the atmospheric composition. In order to handle the large data flow, an optimized code for the Level 2 near real time analysis of MIPAS data was developed by an international consortium of scientists under an ESA contract and was implemented in the ENVISAT Ground Segment. The code is designed to provide, in an automated and continuous mode, atmospheric vertical profiles of temperature and pressure, as well as of concentrations of O3, H2O, CH4, HNO3, N2O and NO2, in the altitude range from 6 to 60 km. The commissioning phase, in which verification and validation of the instrument and of the analysis code are performed, is still in progress, but some preliminary results have been obtained. The first examples of the MIPAS near real time Level 2 data products, consisting of retrieved profiles and auxiliary data that characterize the measurement accuracy and resolution, are shown.

Stratospheric composition from balloon-based measurements

The chemical composition of the lower stratosphere has been measured using a polarizing interferometer operating in the far infrared and submillimetric spectral region. The instrument was flown three times (in 1992, 1993 and 1994) from the NSBF balloon base (Fort Sumner, New Mexico) in coincidence with overpasses of the UARS satellite, for a total of about 50 hours of measurements. In this paper we report some of the results obtained from the data analysis made up to now.

The global picture of the atmospheric composition provided by MIPAS on Envisat

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a mid-infrared emission spectrometer which is part of the core payload of the Envisat satellite, launched by ESA in March 2002. It provides unique observations of the atmospheric spectral radiances in the 4.15 - 14.6 μm spectral interval with innovative limb scanning capabilities for the three dimensional observation of the atmospheric composition and processes. The species, the processes and events that have been studied with this instrument in its 10 years of operation are briefly reviewed.

Optimized forward and retrieval model for MIPAS near-real-time data processing

The IR emission limb sounder MIPAS will be operated as an ESA core instrument on the ENVISAT-1 satellite. Near real time retrieval of pressure, temperature and volume mixing ratio of five key species from calibrated spectra will be performed in the Level 2 processor of the ENVISAT Payload Data Segment. In order to develop an optimized retrieval algorithm suitable for the implementation in MIPAS Level 2 processor, an ESA supported study is being carried out. In the framework of this study, an optimized forward/retrieval code based on the global fit approach was implemented. In this approach all the spectra of a limb-scanning sequence are simultaneously fitted, so that error propagation in the altitude domain is avoided. The attained accuracy performances of the retrieval code are the following: (i) temperature accuracy < 2 K at all the altitudes covered by the standard MIPAS scan; (ii) tangent pressure error: < 3 percent; (iii) error on the retrieved VMR of the key species: < 5 percent at most of the latitudes of scientific interest covered by the standard MIPAS scan. The run-time required to perform p,T and VMR retrieval of the five MIPAS target species from a limb-scanning sequence of 16 limb-views is less than 6 minutes on a SUN SPARCstation 20. The most effective code optimization were implemented in the radiative transfer model and in the computation of the jacobian of the retrieval.

Recent advances in submillimeter remote sensing of the stratosphere

The capability of remote-sensing measurements of the stratosphere in the submillimetric spectral region is presented. The analysis is discussed of spectra recorder by a balloon-borne Fourier Transform spectrometer that measures the emission of the atmosphere in the submillimetric with the limb-scanning observation technique. Two problems, that have been studied with submillimetric spectroscopy, are presented in detail: the measurement of HBr and the diurnal variability of hydroxyl radical.