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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008
Figure 14 : Raw and low-pass filtered barycentre profile
— Injected micro-vibration
0.3 —Barycentre filtered measure
Figure 15 : Low-pass filtered barycentre profile and injected
micro-vibration
About 90 stars fulfil this condition, but if we focus on stars
brighter than magnitude 1 to ensure a very good accuracy,
about 15 are available (Fig 18) which is enough given that a
same star may be shot several times along the night-orbit.
Figure 18 : Stars candidate for dynamic stability assessment
The absolute location, measured along the line-wise direction,
is very closed to the injected micro-vibration as shown in Fig
15. The profile spectra presented below for a magnitude 1 (Fig
16) give an idea of the micro-vibration restitution accuracy in
amplitude and frequencies. The maximum amplitude deviation
is less than 0.02 PA pixel. Frequency resolution (4.7 Hz in our
example) is given by the observation length.
0.10 —Barycentre filtered measure spectra
Figure 16 : measured and injected micro-vibration spectra
3.7 Stars selection
A requested RMS amplitude accuracy better than 0.10 PA
pixel can be reached with stars brighter than magnitude 2.5
according to Fig 17.
4. CONCLUSIONS
Brand new image calibration methods have been designed and
are still studied thanks to Pleiades-HR satellite agility. These
capabilities offer large operational benefits. Many other specific
acquisitions will be carried out during the commissioning phase.
For instance, radiometric absolute calibration will be
performed using the moon as a photometric benchmark. As for
the stars, they could also be used to assess absolute calibration,
MTF or accurate viewing directions.
ACKNOWLEDGEMENTS
The authors would like to thank Laurent Bernard for his work
on image simulations and Olivier Puig for his studies on stars
radiometric behaviour within Pleiades-HR sensors.
REFERENCES
1. L. Lebegue & al., SPOT5 Radiometric Image Quality,
IGARSS, Toulouse, 2003.
2. Ph. Kubik & al, AMETHIST : A Method for Equalization
Thanks to HISTograms, SPIE, Maspalomas, 2004
3. N. Theret & al, AMETHIST guidance : 3000 eyes focused
on the same spot, SpaceOps, Rome, 2006