LITE
Three-line
ing
mospheric
r practical
pheric and
| by multi-
bservation
s followed
ERS-1 has
Advanced
solar array
c and 16m
tion of the
Iti-channel
gust 2002.
Takhasi Hamazaki
The resolution of the panchromatic channel is
improved to 2.5m. The multi-spectral and L-band
SAR resolution is 10m.
Star Tracker
1.2 ALOS Overview
Mission objective of the ALOS is to advance land-
observing technology and to contribute to
cartography, ^ regional ^ observation, disaster
monitoring and Earth resources survey. The ALOS
has three major sensors; Panchromatic Remote
Sensing Instruments for Stereo Mapping (PRISM),
Advanced Visible and Near Infrared Radiometer type
2 (AVNIR-2) and Phased Array type L-band
Synthetic Aperture Radar (PALSAR). ALOS
launch configuration is shown in Fig.2. The ALOS
is planned for launch in August 2002 by the H-IIA
launch vehicle from Tanegashima Space Center in
Japan.
Data Relay
Antenna
Fig.2 ALOS Launch Configuration
2 ALOS SENSORS
2.1 PRISM
The PRISM is what is called a three line sensor and provides 2.5m resolution image and 3 to 5meter accuracy Digital
Elevation Model with triplet stereo mapping capability. The PRISM consists of three optics that look nadir, forward,
and backward respectively. Base to height ratio between forward and backward optics is equal to one. Observation
swath width is 35km in triplet stereo observation mode and 70km in nadir observation mode. This data is mainly for
cartography and will be used to generate and revise 1/25,000 scale maps and digital data for Geographical Information
System (GIS). The Geographical Survey Institute of Japan (GSI) that is the Japanese national mapping authority is
expected to be a biggest user for PRISM data. Offset-axis triplet mirror optics and higher order aspheric surface
mirror is developed in order to realize the unique combination of high-resolution and wide swath width for the PRISM.
Size of the primary aperture mirror is 600mm by 300mm. Eight 5000-pixel linear CCDs are allocated on the 300mm
length half mirror prism and works as a 40,000 pixels linear array sensor. Thermal distortion of the PRISM internal
truss structure must be minimized in order to achieve both 3 to Smeter altitude determination accuracy and 2.5 meter
position determination accuracy. This is realized by the accommodation of integrated optical bench concept, that is,
three optics, star trackers, and attitude sensor unit, and jitter sensors are integrated on one rigid optical bench and
temperature of the entire optical bench is controlled within plus and minus 3 degree Kelvin. PRISM optical bench
concept is shown in Fig.3 and PRISM characteristics is shown in Table.1.
PRISM (Forward)
PRISM (Bacward)
Number of Optics 3
Wave Length 0.52-0.77 x10um
| Base/Height Ratio 1.0
IFOV 2.5m
Swath Width 70km(Nadir)/ C C
35km(Forward, Nadir,
Backward) PRISM (Nadir)
S/N >70 Star trackers
MTF 23
Table 1 PRISM characteristics Fig.3 PRISM Optical Bench
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part Bl. Amsterdam 2000. 137
