Browsing by Author "Bracher, A."

Now showing 1 - 4 of 4
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    Current retrieval and inter-comparisons results of Sciamachy Nighttime Nox
    (Institute of Environmental Physics and Remote sensing, 2014) Amekudzi, L. K.; Bramstedt, K.; Bracher, A.; Rozanov, A.; Bovensmann, H.; Burrows, J. P.
    Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) performs lunar occultation measurements over the high southern latitude (50o S–90o S). Using the global spectra fitting method by the differential optical depth approach and the optimal estimation method, vertical profiles of nighttime NOx (NO2 and NO3) are retrieved. The quality of the retrieved NOx products are verified by comparing SCIAMACHY nighttime NO2 result with other satellite instruments (HALOE and SAGE II) and NO3 results with a simple chemical model outputs. Very promising results are obtained. The relative mean differences (rmd) of SCIAMACHY-HALOE comparisons are within -16 % to +3 % and the standard deviations (rms) within 4–16 % between 25–38 km. The rmd and rms for SCIAMACHYSAGE II comparisons are within -9 % to +7 % and 10– 17 % between 22–39 km. The retrieved NO3 are in very good agreement with the model calculations between 16 to 38 km within accuracy of 25 %.
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    Nighttime nox from sciamachy lunar occultation measurements
    (Proc. of the First ‘Atmospheric Science Conference’, ESRIN, 2006-05) Amekudz, L. K.; Bracher, A.; Bramstedt, K.; Bovensmann, H.; Burrows, J. P
    Vertical profiles of stratospheric NO2 and NO3 have been retrieved from moderately resolution atmospheric lunar transmission spectra measured by SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) on board the ENVISAT (Environmental Satellite). The measurements were taken over the high Southern latitude (50o S–90o S). The global spectra fitting method by differential optical depth approach were used to fit NO2 and NO3 using the spectral window of 430–460 nm and 615–680 nm respectively. To assess the accuracy of the retrieved NO2 profiles the SCIAMACHY nighttime NO2 profiles were compared with daytime NO2 profiles measured by Halogen Occultation Experiment (HALOE), using photochemical correction model. The validation results show that the quality of SCIAMACHY nighttime NO2 is high within 5–20% in the altitude range of 24–39 km. Our current understanding of NO3 chemistry and the internal consistency of the retrieved NO3 profiles were verified with a complex and a relatively simple model scheme. The complex model uses a comprehensive photochemistry of the stratosphere and the simple model uses only SCIAMACHY ozone and ECMWF temperature and pressure analyses as input. We found that the retrieved NO3 profiles are in very good agreement with the model calculations within the expected accuracy of 20–35 %.
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    Sciamachy solar and lunar occultation: validation of ozone, No2 and No3 profiles
    (ESRIN, 2007-02) Amekudzi, L. K.; Bramstedt, K.; Bracher, A.; Rozanov, A.; Bovensmann, H.; Burrows, J. P.
    Using a global spectra fitting method by the differential optical depth within the radiative transfer and retrieval code SCIATRAN 2.1, vertical profiles of stratospheric traces gases are derived from SCIAMACHY solar and lunar occultation transmission spectra. From solar occultation observations ozone and NO2 profiles have been retrieved, from lunar occultation measurements ozone, NO2, and NO3 profiles have been derived. To access the quality of the SCIAMACHY occultation retrieved products a validation study was carried out, by comparing the retrieved ozone and NO2 profiles to correlative observations of other satellite instruments. These instruments are the Halogen Occultation Experiment (HALOE), the second Stratospheric Aerosol and Gas Experiment (SAGE II), and The third Polar Ozone and Aerosol Measurement (POAM III) . The NO3 profiles are compared with results from a photochemical model scheme. The validation show good results for SCIAMACHY occultation products. In solar occultion, the deviation of ozone is mostly within 0 % to +10 % for ozone and within 20 % for NO2 over a wide altitude range. In lunar occultation, the agreement is +10% to +20 % for ozone and within 20 % ˙ for NO2 in the main part of the profiles. The NO3 results show good agreement with the model outputs within the accuracy of 35 %.
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    Sciamachy solar occultation: ozone and No2 profiles 2002-2006
    (ENVISAT, 2007-07) Bramstedt, K.; Amekudzi, L. K.; Bracher, A.; Rozanov, A.; Bovensmann, H.; Burrows, J. P.
    The spectrometer SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) on-board ENVISAT is measuring solar irradiances and Earthshine radiances from the UV to the NIR spectral region in nadir, limb and lunar/solar occultation geometry. Solar occultation measurement are performed during sunrise at northern latitudes (49N to 69N, depending on season). Using an optimal estimation approach with the radiative transfer and retrieval code SCIATRAN 2.1, these measurements are used to derive vertical profiles of ozone and NO2. Precise tangent height information is derived from the scanning over the solar disk. Here we present an almost complete dataset from August 2002 to December 2006, including validation results with independent measurements from other satellites.