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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