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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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doi:10.5194/amt-2016-397
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
09 Jan 2017
Review status
This discussion paper is under review for the journal Atmospheric Measurement Techniques (AMT).
Improved pointing information for SCIAMACHY from in-flight measurements of the viewing directions towards sun and moon
Klaus Bramstedt1, Thomas C. Stone2, Manfred Gottwald3, Stefan Noël1, Heinrich Bovensmann1, and John P. Burrows1 1Institute of Environmental Physics (IUP), University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany
2US Geological Survey, 2255 North Gemini Drive, Flagstaff, AZ 86001, USA
3German Aerospace Center, Remote Sensing Technology Institute, Münchner Str. 20, 82234 Wessling, Germany
Abstract. The SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) on Envisat (2002–2012) performed nadir, limb, solar/lunar occultation and various monitoring measurements. The pointing information of the instrument is determined by the attitude information of the Envisat platform with its star trackers together with the encoder readouts of both the azimuth and the elevation scanner of SCIAMACHY.

In this work, we present additional sources of attitude information from the SCIAMACHY measurements itself. The basic principle is the same as used by the star tracker: We measure the viewing direction towards celestial objects, i.e. sun and moon to detect possible mispointings.

In sun over limb port observations, we utilise the vertical scans over the solar disk. In horizontal direction, SCIAMACHY's sun follower device (SFD) is used to adjust the viewing direction. Moon over limb port measurements use for both the vertical and the horizontal direction the adjustment by the SFD. The viewing direction is steered towards the intensity centroid of the illuminated part of the lunar disk. We use reference images from the USGS Robotic Lunar Observatory (ROLO) to take into account the inhomogeneous surface and the variations by lunar libration and phase to parameterise the location of the intensity centroid from the observation geometry. Solar observations through SCIAMACHY's so-called sub-solar port (with a viewing direction closely to zenith) use in vertical direction also the SFD. In horizontal direction the geometry of the port defines the viewing direction.

Using these three type of measurements, we fit improved mispointing parameters by minimising the pointing offsets in elevation and azimuth. The geolocation of all retrieved products will benefit from this, especially the altitudes assigned to SCIAMACHY's limb and occultation products will be improved.


Citation: Bramstedt, K., Stone, T. C., Gottwald, M., Noël, S., Bovensmann, H., and Burrows, J. P.: Improved pointing information for SCIAMACHY from in-flight measurements of the viewing directions towards sun and moon, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-397, in review, 2017.
Klaus Bramstedt et al.
Klaus Bramstedt et al.
Klaus Bramstedt et al.

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Short summary
The satellite instrument SCIAMACHY on-board the ESA's platform Envisat (2002–2012) performed observations of the Earth's atmosphere. Using sun and moon observations of the instrument itself, we derived a set of correction parameters for the determination of the viewing directions of the instrument. From this work, all vertical profiles of atmospheric parameters from SCIAMACHY's limb and occultation measurements will be improved by a more accurate altitude information.
The satellite instrument SCIAMACHY on-board the ESA's platform Envisat (2002–2012) performed...
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