Intercomparison of non-LTE radiative transfer codes
STUD GEO OP (2001) 765-768
Abstract:
Limb infrared spectra calculated by the KOPRA, GENLN2, RFM, and SPIRT radiative transfer algorithms were intercompared with special emphasis on non-local thermodynamic equilibrium emission. The overall agreement is usually better than approximately 0.5 percent except for single phenomena which have been assessed in more detail. Most spectral radiance discrepancies occur also under local thermodynamic equilibrium conditions and are attributed to different treatment of far wings of lines, integration schemes and mass-weighted averaging of atmospheric state temperature and pressure along slant path segments, as well as different spectral sampling during the calculation of monochromatic radiances. Additional differences in the non-local thermodynamic equilibrium case are presumably due to the different treatment of inhomogeneities of vibrational temperatures with height during numeric integration of radiative transfer.Retrieval from high resolution remote sounding instruments
STUD GEO OP (2001) 803-806
Abstract:
Atmospheric measurements from new high spectral resolution remote sensing instruments will contain a huge amount of information. To use these data efficiently it is necessary to select a subset of the measurements for use in the retrieval of atmospheric profiles. The use of sections of spectrum, 'microwindows', increases the efficiency of forward model calculations. An objective scheme has been developed to select microwindows, which are optimal in spectral and altitude range, using the reduction in retrieval error. The method has been applied to MIPAS-B measurements, a balloon-borne Fourier transform infrared spectrometer. Results show reasonable retrieval errors. An assessment of the best achievable accuracy has been made, and the most important error sources are thus demonstrated.Optimized spectral microwindows for data analysis of the Michelson Interferometer for Passive Atmospheric Sounding on the Environmental Satellite.
Appl Opt 39:30 (2000) 5531-5540
Abstract:
For data analysis of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) atmospheric limb emission spectroscopic experiment on Environmental Satellite microwindows, i.e., small spectral regions for data analysis, have been defined and optimized. A novel optimization scheme has been developed for this purpose that adjusts microwindow boundaries such that the total retrieval error with respect to measurement noise, parameter uncertainties, and systematic errors is minimized. Dedicated databases that contain optimized microwindows for retrieval of vertical profiles of pressure and temperature, H2O, O3, HNO3, CH4, N2O, and NO2 have been generated. Furthermore, a tool for optimal selection of subsets of predefined microwindows for specific retrieval situations has been provided. This tool can be used further for estimating total retrieval errors for a selected microwindow subset. It has been shown by use of this tool that an altitude-dependent definition of microwindows is superior to an altitude-independent definition. For computational efficiency a dedicated microwindow-related list of spectral lines has been defined that contains only those spectral lines that are of relevance for MIPAS limb sounding observations.Optimized forward model and retrieval scheme for MIPAS near-real-time data processing.
Appl Opt 39:8 (2000) 1323-1340
Abstract:
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.A new technique for evaluating mesospheric momentum balance utilizing radars and satellite data
Annales Geophysicae 18:4 (2000) 478-484