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| Titel |
Characterization of MIPAS elevation pointing |
| VerfasserIn |
M. Kiefer, T. Clarmann, U. Grabowski, M. Laurentis, R. Mantovani, M. Milz, M. Ridolfi |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 7, no. 6 ; Nr. 7, no. 6 (2007-03-26), S.1615-1628 |
| Datensatznummer |
250004833
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| Publikation (Nr.) |
 copernicus.org/acp-7-1615-2007.pdf |
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| Zusammenfassung |
| Sufficient knowledge of the pointing is essential for analyses of
limb emission measurements.
The scientific retrieval processor for MIPAS on ENVISAT operated at IMK
allows the retrieval of pointing information in terms of tangent altitudes
along with temperature.
The retrieved tangent altitudes are independent of systematic offsets
in the engineering Line-Of-Sight (LOS) information delivered with the ESA
Level 1b product.
The difference of pointing retrieved from the reprocessed high
resolution MIPAS spectra and the engineering pointing information
was examined with respect to spatial/temporal behaviour.
Among others the following characteristics of MIPAS pointing could be
identified:
Generally the engineering tangent altitudes are too high by 0–1.8 km
with conspicuous variations in this range over time.
Prior to December of 2003 there was a drift of about 50–100 m/h, which was
due to a slow change in the satellite attitude.
A correction of this attitude is done twice a day, which leads to
discontinuities in the order of 1–1.5 km in the tangent altitudes.
Occasionally discontinuities up to 2.5 km are found, as already reported from
MIPAS and SCIAMACHY observations.
After an update of the orbit position software in December 2003
values of drift and jumps are much reduced.
There is a systematic difference in the mispointing between the
poles which amounts to 1.5–2 km, i.e. there is a conspicuous orbit-periodic
feature.
The analysis of the correlation between the instrument's viewing angle
azimuth and differential mispointing supports the hypotheses that a
major part of this latter phenomenon can be attributed to an error in the roll angle
of the satellite/instrument system of approximately 42 mdeg.
One conclusion is that ESA level 2 data should be compared to other data
exclusively on tangent pressure levels.
Complementary to IMK data, ESA operational LOS calibration results were used
to characterize MIPAS pointing.
For this purpose MIPAS is used as a radiometer while the passage of infrared bright stars
through the instrument's field of view is recorded.
Deviation from expected time of passage gives information about mispointing.
Results are: a pronounced seasonal variation of the LOS is seen
before a correction of on-board software took place in December of 2003.
Further a pitch bias of 26 mdeg with respect to the platform attitude information
is found, which corresponds to 1.45 km tangent altitude offset towards low altitudes. |
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