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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 5, issue 11
Atmos. Meas. Tech., 5, 2867–2880, 2012
https://doi.org/10.5194/amt-5-2867-2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Meas. Tech., 5, 2867–2880, 2012
https://doi.org/10.5194/amt-5-2867-2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 27 Nov 2012

Research article | 27 Nov 2012

Precise pointing knowledge for SCIAMACHY solar occultation measurements

K. Bramstedt1, S. Noël1, H. Bovensmann1, M. Gottwald2, and J. P. Burrows1 K. Bramstedt et al.
  • 1Institute of Environmental Physics (IUP), University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany
  • 2German Aerospace Center, Remote Sensing Technology Institute, Münchner Str. 20, 82234 Wessling, Germany

Abstract. We present a method to precisely determine the viewing direction for solar occultation instruments from scans over the solar disk. Basic idea is the fit of the maximum intensity during the scan, which corresponds to the center of the solar disk in the scanning direction. We apply this method to the solar occultation measurements of the satellite instrument SCIAMACHY, which scans the Sun in elevation direction. The achieved mean precision is 0.46 mdeg, which corresponds to an tangent height error of about 26 m for individual occultation sequences. The deviation of the derived elevation angle from the geolocation information given along with the product has a seasonal cycle with an amplitude of 2.26 mdeg, which is in tangent height an amplitude of about 127 m. The mean elevation angle offset is −4.41 mdeg (249 m). SCIAMACHY's sun follower device controls the azimuth viewing direction during the occultation measurements. The derived mean azimuth direction has an standard error of 0.65 mdeg, which is about 36 m in horizontal direction at the tangent point. We observe also a seasonal cycle of the azimuth mispointing with an amplitude of 2.3 mdeg, which is slightly increasing with time. The almost constant mean offset is 88 mdeg, which is about 5.0 km horizontal offset at the tangent point.

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