In early 1995, Hanshin area in the west part of Japan 
suffered severe damage from a tremendous earthquake. 
Dislocations of land and soil liquefaction, which were 
caused by the earthquake, were observed by the SAR 
interferometry and the high-resolution optical sensors. 
The usefulness of such kind of satellites for hazard 
monitoring was confirmed (Sudo et a/.,1995). The users' 
requirements for hazard monitoring are “as prompt as 
possible” and “as precise as possible”. According to our 
study, to choose adequate orbit and employ cross-track 
pointing mechanisms of the sensors let a polar orbiting 
satellite to observe damaged area within 48 hours. 
3. ALOS SATELLITE SYSTEM 
In order to accommodate high performance sensors, the 
ALOS satellite system should have several outstanding 
capabilities. First one is precise determination of position 
and attitude, and second one is mass data handling 
capability. The ALOS equips a star-tracker for accurate 
attitude determination and carrier phase tracking Global 
Positioning System (GPS) receivers for precise position 
determination. The position and attitude accuracies of 
the ALOS will be set to achieve the requirements from the 
geometric accuracies and the derived height accuracies 
of the sensor data. 
To handle huge data generated by the AVNIR-2 and the 
PALSAR, the ALOS has mass data memories on board. 
The memories should have 706 Gbits storage capacity 
and 240 Mbps data handling capability. The candidates 
for these mass memories are optical data recorders and 
solid state memory recorders. The ALOS also equips a 
high data rate transmission capability through the Data 
Relay Technology Satellites (DRTS) scheduled to be 
launched before the ALOS's launch. They allow us to get 
ALOS data in real time for hazard monitoring. Table 1 
shows the ALOS satellite system characteristics, and 
figure 1 gives its in-orbit configuration. 
Table 1. ALOS Satellite System characteristics 
Launch 2002 
Launch vehicle H-11A 
Spacecraft mass about 3,850 kg 
  
Generated power about 7 kW 
Orbit sun-synchronous 
near recursive 
-altitude 720 +/- 60 km 
-inclination 98 degree 
-repeat cycle 45-52 days 
-local time at 10h 30m am 
descending node 
Mission instruments 
AVNIR-2, PALSAR, DCS 
194 
4. PALSAR CHARACTERISTICS 
The PALSAR is the Japanese second spaceborne SAR 
using L-band frequency and will have a cross-track 
pointing capability from 18 to 55 degrees of incidence 
angle. Table 2 summarizes the PALSAR characteristics 
as well as the JERS-1/SAR's. 
4.1 Observation Modes 
The PALSAR basically has three modes in its 
observation, such as fine resolution, ScanSAR , and low 
data rate modes. The fine resolution mode, a strip SAR, is 
a conventional mode and mainly used for detailed 
regional observations and repeat-pass interferometry. 
The goal of this mode is to achieve 10 meters of spatial 
resolution both in range and azimuth directions, 70 km of 
swath width, -25 dB of noise equivalent backscattering 
coefficient (NEc’), and 25 dB of Signal-to-Ambiguity 
(S/A) ratio at a look-angle of 35 degrees. Its signal to 
noise ratio was determined from the average 
backscattering coefficient of natural targets and the 
accuracy of elevation determination by using SAR 
interferometry. The PALSAR’s S/A level is about 10 dB 
higher than that of JERS-1/SAR's, and will improve data 
quality especially in the coastal region. A five bits 
quantization excludes a Sensitivity Time Control (STC) of 
the receiver and phase errors at the changing points of 
the receiver gain. 
The PALSAR will have another attractive observation 
mode which is the ScanSAR mode. This mode will allow us 
to get about more than 250 km width of SAR images by 
sacrificing spatial resolution, which is about three times 
wider than conventional SAR (e.g. JERS-1/SAR) images 
and is considered to be useful for sea ice extent and 
rainforest monitoring. When we use an optimized orbit, by 
using pointing and ScanSAR capabilities, we can get the 
data from the same target area in less than five days. 
The observed data in the low data rate mode can be 
transmitted directly to the ground stations by using X- 
band frequency. Because of narrow band width in the X- 
band down-link frequency, the maximum data rate in this 
band is limited to 120 Mbps. By sacrificing spatial 
resolution in range direction, dynamic range, and swath 
width of the fine resolution mode, we can transmit the 
observation data either in 120 Mbps or 60 Mbps. Even in 
the 60 Mbps data, the data quality may be almost as 
same as the JERS-1/SAR's. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B1. Vienna 1996