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SPOTS IN-FLIGHT COMMISSIONING : 
INNER ORIENTATION OF HRG AND HRS INSTRUMENTS 
R. Gachet CNES/IGN, 
roland.gachet @cnes.fr 
  
KEY WORDS : SPOTS, inner orientation, accuracy, Manosque, DTM, image matching 
ABSTRACT: 
Launched on May 2002 the 3", SPOTS is the latest of the SPOT series of satellites continuing and complementing the mission 
assigned to its predecessors in the field of Earth Observation and Mapping. In order to optimize the various improvements of the 
platform and of the payload the CNES has carried out, for the first time, an accurate determination of the inner orientation of the 
instruments. This paper details the method involved in this determinaation and the results obtained. 
RESUME : 
Lancé le 3 mai 2002, SPOTS est le dernier né de la famille des satellites SPOT continuant et complétant la mission de ses 
prédécesseurs dans le domaine de l'Observation de la Terre et la Cartographie. Les multiples évolutions dans la définition de sa 
plateforme ainsi que de sa charge utile ont conduit le CNES à réaliser pour la premiére fois une détermination fine de l'orientation 
interne des instruments. Cet article présente la méthode mise en oeuvre et les résultats obtenus lors de cette détermination. 
1 -INTRODUCTION 
SPOTS is the latest of the SPOT series of-satellites continuing 
and complementing the mission assigned to its predecessors in 
the field of Earth Observation and Mapping. Launched on 
May 2002 the 3", its in-flight commissioning was led in two 
phases. The qualification phase permitted to hand over the 
satellite to Spot Image in july 2002 [Bouillon 2002,2003], 
[Breton 2002]. The second phase included fine tuning of its 
components and continued until early 2003 allowing to fully 
take advantage of the geometric improvements brought to 
SPOTS compared to its elders : 
* star tracker and improved steering mirror on HRG 
instruments for the localization, 
* monolithic CCD array, 
* resolution, 
* along track stereoscopic instrument HRS. 
Observations on the first SPOT 5 images showed 
imperfections in the CCD array and telescop alignments both 
on HRG and HRS instruments. An inner orientation of the 
instruments was therefore considered necessary, especially for 
the HRS stereoscopic instrument with an optical distorsion of 
several pixels. Following is a non exhaustive list of the 
outcomes expected from this inner orientation : 
* assessed and refined look angle models provided by 
the satellite constructor ; 
* optimized relative orientation between the forward and 
backward HRS stereoscopic instruments ; 
* optimized relative orientation between the 
panchromatic and multispectral bands within each 
HRG instrument. 
On previous SPOT satellites the geometric performance of the 
detectors has been assessed with relative methods [Valorge 
2003] involving simultaneous acquisitions of the same scene 
with both instruments ; these methods never permitted to 
obtain an absolute measurement of the viewing directions 
[Gachet 1999]. The characteristics of SPOTS instruments 
together with the objective of inner orientation made it 
necessary to implement another method based on absolute 
calibration using airborne images and elevation information 
from our « super site » in southeastern France. 
Since March 2003, ancillary data provided in the 
« METADATA.DIM » file associated with SPOTS images 
[Spot Image 2002] include the instruments look angles for 
each detector with an estimated RMS accuracy of 0.03 pixel. 
2 -THE MANOSQUE SUPERSITE 
2.1 The supersite characteristics 
Since early 1999, CNES has worked on defining and equiping 
a supersite for its image quality assessment needs. Various 
criteria guided the definition of this supersite involving both 
the SPOT satellites characterictics and the image quality 
assessment methods. 
2.1.1 Measurement quality through image matching : the 
accuracy that can be obtained using image matching technics 
depends on such parameters as 
* the level of information to be matched, forbiding sites 
with radiometrically uniform areas 
the radiometric similarity between data to match (MTF, 
spectral bands, seasonal and long term diachrony, ...) . 
Hence the reference data must comply with the 
radiometric characteristics of the SPOTS imagery, with 
a relatively slowly evoluting landuse, forbiding highly 
cultivated sites. 
2.1.2 Geometric quality of the reference data : both 
planimetric and altimetric accuracy of reference data over the 
« supersite » must be controlled. 
* Planimetry should be controlled through particularly