Instabilities in retrieval of atmospheric trace gas profiles caused by the use of atmospheric level models

Apodization effects in the retrieval of volume mixing ratio profiles

In remote sensing applications, spectra measured by Fourier-transform spectrometers are routinely apodized. A rigorous analysis approach would explicitly account for correlations induced in the covariance matrix by apodization, but these correlations are often ignored to simplify and speed up the processing. Using spectra measured by the Atmospheric Trace Molecule Spectroscopy missions, we investigated the effect of apodization on the retrieval of volume mixing ratio profiles for the case in which these correlations are ignored. Minor discrepancies occur between results for apodized and unapodized spectra, particularly when lines with a low signal-to-noise ratio are fitted. A set of microwindows is reported for O3 in the range of 1550-3350 cm(-1).

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

An optimized code to perform the near-real-time retrieval of profiles of pressure, temperature, and volume mixing ratio (VMR) of five key species (O(3), H(2)O, HNO(3), CH(4), and N(2)O) from infrared limb spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) experiment on board the European Space Agency (ESA) Environmental Satellite ENVISAT-1 was developed as part of a ESA-supported study. The implementation uses the global fit approach on selected narrow spectral intervals (microwindows) to retrieve each profile in sequence. The trade-off between run time and accuracy of the retrieval was optimized from both the physical and the mathematical points of view, with optimizations in the program structure, in the radiative transfer model, and in the computation of the retrieval Jacobian. The attained performances of the retrieval code are noise error on temperature <2 K at all the altitudes covered by the typical MIPAS scan (8-53 km with 3-km resolution), noise error on tangent pressure <3%, and noise error on VMR of the target species <5% at most of the altitudes covered by the standard MIPAS scan, with a total run time of less than 1 min on a modern workstation.

Retrieval of atmospheric O(3), HNO(3), CFC-11, and CFC-12 profiles from MIPAS-B-89 limb emission spectra

During the night from May 17 to May 18, 1989, the first of four flights of the Michelson Interferometer for Passive Atmospheric Sounding, Balloon-borne version (MIPAS-B) instrument took place from the Centre National d'Etudes Spatiales balloon-launching site at Aire-sur-l'Adour (France, 44° N latitude). From approximately 33 km float altitude, stratospheric and tropospheric limb infrared emission spectra have been recorded by this novel type of fast-scanning interferometer. Although the measured spectra did not reach the expected quality and the a priori information on the corresponding viewing directions was coarse, the data were processed successfully with a retrieval algorithm specially adapted for application to noisydata. Mixingratio profiles of ozone, nitric acid, CFC-11, and CFC-12 havebeen retrieved from limb sequences of wide spectral intervals by nonlinear least-squares fitting in combination with a layer-bylayer onion-peeling approach. A rigorous error analysis has been carried out by means of Monte Carlo calculations.