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21 February 2001 Retrieval of PSC properties from MIPAS-ENVISAT measurements
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The possibility to derive microphysical properties of polar stratospheric clouds from future MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) -- ENVISAT measurements was investigated. Available refractive index data for PSC candidates were intercompared in order to estimate their reliability. Especially for NAT the laboratory measurements differ significantly and for ternary H2SO4/HNO3/H2O solutions only one source of data exists. For simulating limb-spectra, a Mie model was implemented in the forward code KOPRA (Karlsruhe Optimized and Precise Radiative transfer Algorithm) in such a way that in parallel to the radiance spectra the derivatives with respect to a variety of microphysical aerosol parameters can be generated. Broadband forward calculations for small and large aerosols were made for various refractive indices. For large particles the PSC signal in the spectrum was up to forty times larger than the noise level. The signal for small particles was around the spectral noise. By minimizing the total retrieval error an automatic microwindow selection was performed for different PSC scenarios. Under the assumption of known radius and width of the aerosol size distribution resulting errors for number density retrieval were less than 3% (9 X 10-4 cm-3) for large and around 50% (7 cm-3) for small particles. For large particles it is possible to perform a two-parameter fit of number density and mode radius with errors less than 10%. Due to the Rayleigh- limit a distinction between radius and number density is not possible for small particles. However, the volume density can be derived with 12% (0.4 micrometer3/cm-3) uncertainty for large and 20% (2.2 X 10-2 micrometer3/cm-3) for small aerosols. These conclusions are valid as long as the aerosol layer is not optically thick which in our examples was the case for water ice (type II) PSCs of number density 0.2 cm-3 and radius 2.6 micrometer.
© (2001) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Michael Hoepfner, Thomas von Clarmann, Georg Echle, and Alexandra Zimmermann "Retrieval of PSC properties from MIPAS-ENVISAT measurements", Proc. SPIE 4150, Optical Remote Sensing of the Atmosphere and Clouds II, (21 February 2001);

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