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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part Bl. Istanbul 2004 
  
1. INTRODUCTION 
The HRS Scientific Assessment Program is a new initiative 
for CNES and its partners in the SPOT program. It is the first 
time that an international user community (ISPRS) is 
formally associated to the scientific assessment of the 
"system" quality of a satellite, in this case SPOT 5 and 
especially its new instrument HRS (High Resolution 
Stereoscopic) 
The results of this program, to be presented during the next 
ISPRS Congress in Istanbul, July 2004, should help CNES to 
improve its future Earth Observation systems (such as 
Pléiades: Baudoin 2004) and all users to better know and 
trust the accuracy and quality of the HRS instrument and of 
the derived DEM. 
2. SPOT 5 
SPOT 5 is the latest satellite of the SPOT family, launched 
during the night of the 3" to the 4^ of May 2002 from the 
European Spaceport in Kourou (French Guyana) with one of 
the last Ariane 4 to be used. (Flight V151 with ARA2P) 
This satellite (Fig 1) ensures data continuity with the 
previous satellites but provides also enhanced images (at 2.5 
m resolution with its two HRG instruments) and new 
stereoscopic capabilities with the HRS instrument. A fourth 
imaging sensor, Vegetation 2 (recurrent model of Vegetation 
1 on SPOT 4) gives a wide-swath (2500 km) daily coverage. 
A star tracker is used to get better attitude measurements and 
therefore better image location. 
High Resolution Geometry 
Instrument 
  
i 
n Star 
1 
m sensor 
        
   
Vegetation : 
Doris Antenna ' 
  
High Resolution 
Stereo Instrument 
Fig 1: Spot 5 satellite and payloads 
3. HRS CHARACTERISTICS 
The High Resolution Stereoscopic instrument (HRS) has 
already been described (Fratter, 2001; Bernard, 2001, 
Gleyzes, 2003) Figures of the instrument (Fig.2), of its optics 
(Fig.3) and its main technical characteristics (Table 4) are 
presented below. With two telescopes HRS acquires nearly 
simultaneous stereo pairs (at 90-second interval) of 120-km 
swath, along the track of the satellite, with a B/H ratio of 
about 0.8. 
  
Fig 2: HRS instrument 
wl 
  
Fig 3: HRS optics and detection unit 
A continuous strip of 600 km length can be covered 
stereoscopically with 10 m ground resolution across track and 
with 5m ground sampling distance along track (parallax 
lines). (Fig. 5) 
  
HRS characteristics 
  
  
  
  
  
Mass 90 kg 
Power 128 W 
Size 1.0x 1.3 x 0.4 m° 
Panchromatic band 0.48-0.70 um 
Ground sampling distance 10 m cross-track, 
5 m along track 
  
Field of view/swath width +/-4° 120 km 
  
  
  
  
  
  
  
  
Focal length 0.580 m 
Detectors per line 12,000 
Detector size 6.5 um 
Integration time/ line 0.752 ms 
Fore/aft viewing angle +/- 20° 
Signal / Noise Ratio > 120 
MTF 240.25 
  
  
  
Table 4: HRS characteristics