Anu Dudhia

Abstract:

When retrieving atmospheric parameters from radiance spectra, the forward modelling of radiative transfer through the Earth's atmosphere plays a key role, since inappropriate modelling directly maps on to the retrieved state parameters. In the context of pre-launch activities of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) experiment, which is a high resolution limb emission sounder for measurement of atmospheric composition and temperature, five scientific groups intercompared their forward models within the framework of the Advanced MIPAS Level 2 Data Analysis (AMIL2DA) project. These forward models have been developed, or, in certain respects, adapted in order to be used as part of the groups' MIPAS data processing. The following functionalities have been assessed: the calculation of line strengths including non-local thermodynamic equilibrium, the evaluation of the spectral line shape, application of chi-factors and semi-empirical continua, the interpolation of pre-tabulated absorption cross sections in pressure and temperature, line coupling, atmospheric ray tracing, the integration of the radiative transfer equation through an inhomogeneous atmosphere, the convolution of monochromatic spectra with an instrument line shape function, and the integration of the incoming radiances over the instrument field of view. © 2003 Elsevier Science Ltd. All rights reserved.

Abstract:

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 optimised 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 O-3, 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 characterise the measurement accuracy and resolution, are shown.