International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part BI. Istanbul 2004 
  
  
  
Reaction wheel step. 
  
PDL dive me ws 
AVNIR-2 mirror drive — 
PALSAR modes 
DRC/Boom modes ===: 
Star Tracker (STT) 
GPS receiver! (GPSR) 
Inertial Reference Unit (IRU) 
Time (sec) 10 107 10? 10° 104 106 
Frequency (Hz) 101 10? 10? 107? 107 10-6 
L T I I I I I J I T T T 
PRISM Sami Scene | Lr 
amoling Mer LLL 
t Am Sk Stereo = 
Q.sm) GSkm) (610-6 36km) ae orem) Seascnal change... 
Environment asserens y tuna 
DRC antenna slug cosmos: 
DRG step — 
PDL modes 
Attitude control bandwidth 
EATS 
Angular Displacement Sensor (ADS) 
        
   
  
  
ae t 
  
  
Attitude determination bandwidth 
Figure 3. Frequency characteristics of PRISM sampling, expected attitude fluctuations, and attitude/orbit determination sensors 
(Modified from Iwata et al., 2002) 
Data flow om pues 
1B1 }— |1B 
5 
de 
  
  
iLevel 11 1A 
^ Work flow $ 
libratiio 
  
   
  
  
Relative alignment between CCD 
  
  
  
  
Pointing/attitude 
Determination accuracy 
  
Rational Polynomial 
Camera (RPC) inodel 
| Stereo pair 
  
  
Stability 
Control accuracy ; 
Geometric correction accuracy ed 
  
  
  
     
Radiometric model | 
a CUT 
  
| Radiometric Calibration =1 
Evaluation of cal. mode data 
Stripe 
Linearity 
Offset and slope 
  
Matching kj Absolute DEM 
ë Y 1 Relative DEM | 
  
  
  
‘MTF, SIN 
“Lossy, JPEG extension 
Matching accuracy 
Co-registration with AVNIR-2 
Ortho Image 
  
  
  
Radiometric Cal. #2) Aim to radiometric 
  
  
Relative accuracy between optics 
  
  
  
  
> accuracy of 1B2 
Absolute calibration 
  
  
  
Figure 4. Work flow of PRISM calibration and validation, and evaluation items 
  
Number of bands ] (Panchromatic) 
  
Wavelength 0.52-0.77 micrometers 
  
Number of optics 
3 (Nadir, Forward, and Backward) 
  
Base to Height ratio 
1.0 (between Forward and Backward) 
  
Spatial resolution 25 in 
  
Swath width 
35 km (Triplet mode) 
70 km (Nadir or Nadir + Backward) 
  
Signal to Noise ratio | > 70 
  
MTF 70.2 
  
Number of detectors | 28,000 (70km swath), 14,000 (35km) 
  
Pointing angle -1.5 to +1.5 deg. (Triplet mode) 
  
Bit length 8 bits/pixel 
  
Data rate 960 Mbps (Triplet mode) 
  
Data compression 
Lossy, JPEG extension (onboard) 
  
Data downlink rate 240 Mbps(1/4.5 compression) 
120 Mbps(1/9 compression) 
  
  
  
  
Table 1. PRISM characteristics 
nadir, forward and backward looking, to achieve alon 
g-track 
stereoscopy. Each telescope consists of three mirrors and six or 
eight Charge Coupled Device (CCD) detectors for push-broom 
scanning. The nadir-looking radiometer can provide 
70 km 
width coverage, and the forward and backward radiometers 
each provide 35 km width coverage. The radiometers are 
installed on both sides of the optical bench, which has precise 
temperature control. Forward and backward radiometers are 
inclined + and — 23.8 degrees from nadir to realize a base-to- 
height ratio of one. Each radiometer has the functions of 
pointing (within + to — 1.5 degree) and cutting electrically to 
obtain the image of the same observed area between other 
radiometers in the cross track direction. Thus, fully overlapped 
three-stereo (triplet) images with a 35 km width are obtained 
without mechanical scanning or yaw steering of the satellite. 
Without this wide Field Of View (FOV), forward-, nadir- and 
backward-looking images would not overlap each other due to 
the Earth's rotation. Pointing angles of + and — 1.25 degrees are 
reasonable to observe the whole coverage by triplet mode in 
global. 
The acquired data are separated into odd- and even-numbered 
detectors, and compressed by lossy compression with Joint 
Photographic Experts Group (JPEG) extension, which are based 
on Discrete Cosine Transform (DCT), quantization, and 
Huffman coding to reduce the downlink data rate from ALOS 
to ground stations. Averaged compression data rates can be 
selected either 1/4.5 or 1/9. 
Internationc 
725 qr 
720 
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z 710 
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595 
690 
685 L 
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= 
Altitude (km 
C 
  
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