Improved pointing information for SCIAMACHY from in-flight measurements of the viewing directions towards sun and moon
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 pl...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2017-07-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/10/2413/2017/amt-10-2413-2017.pdf |
| _version_ | 1828544542586961920 |
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| author | K. Bramstedt T. C. Stone M. Gottwald S. Noël H. Bovensmann J. P. Burrows |
| author_facet | K. Bramstedt T. C. Stone M. Gottwald S. Noël H. Bovensmann J. P. Burrows |
| author_sort | K. Bramstedt |
| collection | DOAJ |
| description | 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.
<br><br>
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.
<br><br>
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) also use the
SFD in the vertical direction. In the horizontal direction the geometry of the port defines the viewing
direction.
<br><br>
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; the
tangent heights are especially improved. The altitudes assigned to SCIAMACHY's solar
occultation measurements are changed in the range of −130 to −330 m, the lunar occultation
measurements are changed in the range of 0 to +130 m
and the limb measurements are changed in the range of −50 to
+60 m (depending on season, altitude and azimuth angle). The horizontal
location of the tangent point is changed by about
5 km for all measurements. These updates are implemented in version 9 of the SCIAMACHY Level 1b
products and Level 2 version 7 (based on L1b version 9). |
| first_indexed | 2024-12-12T02:32:31Z |
| format | Article |
| id | doaj.art-02af7edb984447d685f1633201c61498 |
| institution | Directory Open Access Journal |
| issn | 1867-1381 1867-8548 |
| language | English |
| last_indexed | 2024-12-12T02:32:31Z |
| publishDate | 2017-07-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Measurement Techniques |
| spelling | doaj.art-02af7edb984447d685f1633201c614982022-12-22T00:41:22ZengCopernicus PublicationsAtmospheric Measurement Techniques1867-13811867-85482017-07-01102413242310.5194/amt-10-2413-2017Improved pointing information for SCIAMACHY from in-flight measurements of the viewing directions towards sun and moonK. Bramstedt0T. C. Stone1M. Gottwald2S. Noël3H. Bovensmann4J. P. Burrows5University of Bremen, Institute of Environmental Physics (IUP), Otto-Hahn-Allee 1, 28359 Bremen, GermanyUS Geological Survey, 2255 North Gemini Drive, Flagstaff, AZ 86001, USAGerman Aerospace Center, Remote Sensing Technology Institute, Münchner Str. 20, 82234 Wessling, GermanyUniversity of Bremen, Institute of Environmental Physics (IUP), Otto-Hahn-Allee 1, 28359 Bremen, GermanyUniversity of Bremen, Institute of Environmental Physics (IUP), Otto-Hahn-Allee 1, 28359 Bremen, GermanyUniversity of Bremen, Institute of Environmental Physics (IUP), Otto-Hahn-Allee 1, 28359 Bremen, GermanyThe 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. <br><br> 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. <br><br> 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) also use the SFD in the vertical direction. In the horizontal direction the geometry of the port defines the viewing direction. <br><br> 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; the tangent heights are especially improved. The altitudes assigned to SCIAMACHY's solar occultation measurements are changed in the range of −130 to −330 m, the lunar occultation measurements are changed in the range of 0 to +130 m and the limb measurements are changed in the range of −50 to +60 m (depending on season, altitude and azimuth angle). The horizontal location of the tangent point is changed by about 5 km for all measurements. These updates are implemented in version 9 of the SCIAMACHY Level 1b products and Level 2 version 7 (based on L1b version 9).https://www.atmos-meas-tech.net/10/2413/2017/amt-10-2413-2017.pdf |
| spellingShingle | K. Bramstedt T. C. Stone M. Gottwald S. Noël H. Bovensmann J. P. Burrows Improved pointing information for SCIAMACHY from in-flight measurements of the viewing directions towards sun and moon Atmospheric Measurement Techniques |
| title | Improved pointing information for SCIAMACHY from in-flight measurements of the viewing directions towards sun and moon |
| title_full | Improved pointing information for SCIAMACHY from in-flight measurements of the viewing directions towards sun and moon |
| title_fullStr | Improved pointing information for SCIAMACHY from in-flight measurements of the viewing directions towards sun and moon |
| title_full_unstemmed | Improved pointing information for SCIAMACHY from in-flight measurements of the viewing directions towards sun and moon |
| title_short | Improved pointing information for SCIAMACHY from in-flight measurements of the viewing directions towards sun and moon |
| title_sort | improved pointing information for sciamachy from in flight measurements of the viewing directions towards sun and moon |
| url | https://www.atmos-meas-tech.net/10/2413/2017/amt-10-2413-2017.pdf |
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