Polarization data from SCIAMACHY limb backscatter observations compared to vector radiative transfer model simulations
Author:
Liebing P.,Bramstedt K.,Noël S.,Rozanov V.,Bovensmann H.,Burrows J. P.
Abstract
Abstract. SCIAMACHY is a passive imaging spectrometer onboard ENVISAT, designed to obtain trace gas abundances from measured radiances and irradiances in the UV to SWIR range in nadir, limb and occultation viewing modes. Its grating spectrometer introduces a substantial sensitivity to the polarization of the incoming light with nonnegligible effects on the radiometric calibration. To be able to correct for the polarization sensitivity, SCIAMACHY utilizes broadband Polarization Measurement Devices (PMDs). While for the nadir viewing mode the measured atmospheric polarization has been validated against POLDER data (Tilstra and Stammes, 2007, 2010), a similar validation study regarding the limb viewing mode has not yet been performed. This paper aims at an assessment of the quality of the SCIAMACHY limb polarization data. Since limb polarization measurements by other air- or spaceborne instruments in the spectral range of SCIAMACHY are not available, a comparison with radiative transfer simulations by SCIATRAN V3.1(Rozanov et al., 2012) using a wide range of atmospheric parameters is performed. SCIATRAN is a vector radiative transfer model (VRTM) capable of performing calculations of the multiply scattered radiance in a~spherically symmetric atmosphere. The study shows that the limb polarization data exhibit a large systematic bias which is decreasing with wavelength. The most likely reason for this bias is an instrumental phase shift which changes the relative contributions of different Stokes vector components to the PMD signal as compared to on-ground calibration measurements. It is also shown that it is in principle feasible to recalibrate the polarization sensitivity using the in-flight data and the VRTM simulations, enabling also the monitoring of its degradation. Together with an optimization of the algorithm used to calculate the in-flight polarization data an improved polarization correction can increase the radiometric accuracy of SCIAMACHY limb radiance spectra substantially.
Publisher
Copernicus GmbH
Reference38 articles.
1. Bingen, C. and Fussen, D.: Structure and spectral features of the stratospheric aerosol extinction profiles in the UV-visible range derived from SAGE II data, J. Geophys. Res., 105, 4767–4776, https://doi.org/10.1029/1999JD901109, 2000. 2. Bogumil, K., Orphal, J., Homann, T., Voigt, S., Spietz, P., Fleischmann, O. C., Vogel, A., Hartmann, M., Bovensmann, H., Frerik, J., and Burrows, J. P.: Measurements of molecular absorption spectra with the SCIAMACHY pre-flight model: instrument characterization and reference data for atmospheric remote sensing in the 230–2380 nm region, J. Photochem. Photobiol. A, 157, 167–184, https://doi.org/10.1016/S0010-4655(02)00555-6, 2003. 3. Bolle, H. (Ed.): A Preliminary Cloudless Standard Atmosphere for Radiation Computation, vol. WCP-112, World Climate Research Program, World Meteorological Organization, Geneva, Switzerland, 1986. 4. Bovensmann, H., Burrows, J. P., Buchwitz, M., Frerick, J., Noël, S., Rozanov, V. V., Chance, K. V., and Goede, A. H. P.: SCIAMACHY – {m}ission objectives and measurement modes, J. Atmos. Sci., 56, 127–150, 1999. 5. Bramstedt, K., Noël, S., Bovensmann, H., Burrows, J. P., Lerot, C., Tilstra, L. G., Lichtenberg, G., Dehn, A., and Fehr, T.: SCIAMACHY monitoring factors: Observation and end-to-end correction of instrument performance degradation, in: Proc. Atmos. Sci. Conf., Barcelona, Spain, 7–11 September 2009 (ESA SP-676), ESA, Nordwijk, Netherlands, 2009.
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