18 
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