attitude jitter is random (Normal 
The original SPOT/HRV imagery data 
distribution) image motion within an 
and MTF degraded images are shown in 
exposure time, MTF of the imaging figure 2. 
system is degraded as shown in 
Fig. 1(Ref. 6). 
MTF degradation results in 5.2 Experimental results 
degradation of cross correlation between Table 5 shows a relationship 
image chips of stereo pair. It implies between standard deviation of random 
stereo matching error results in motion of attitude  jitter and DEM 
decreasing DEM estimation accuracy. accuracy degradation. 
5.1 Simulatiorn* of MTF degradation (1) MTF degradation 
In order to generate MIF degraded If the random image motion is 
image, an image motion is simulated with considered for ASTER/VNIR, MTF 
Fast Fourier Transform(FFT). Firstly degradation is shown in Table 5. 
16 of FFT transformed SPOT/HRV data in : : . 
frequency domain are used for MTF degradation implies stereo 
determination of the shifted pixel due matching error results in decreasing DEM 
to random image motion with Normally estimation accuracy. MTF degradation in 
distributed random number. Through this nadir viewing differes from that in 
process, all the pixels at the pixel backward viewing if the random sensor 
location „of one 16th of the pixel motions in both viewings are same. Thus 
interval can be determined. Namely, MTF degradation causes a stereo matching 
analogue image motion is quantized by 4 error. Sensitivities of X, Y and Z 
bits, 16 steps. This process is applied directions on the ground for nadir and 
to SPOT/HRV data in direction of pitch. backward viewings are shown in Table 6. 
Due to the fact that the most dominant 
factor on DEM estimation is attitude 
changes in pitch direction as is shown 
Let us assume that sigma values of 
random image motion in pitch, roll and 
  
in th Dove section so that in this yaw directions are the same and also MTF 
Stud e ane o motion is sinulated in degradations in X, Y and Z directions 
tel direction occures in independently, then the MTF 
P en ; degradations for nadir and backward 
Normal distributed random numbers S : 2 
; : viewings are 15.411 "VS 73.245. This 
with mean of zero and variance of 0.44, implies that df samo sigma value of 
Q n5 aud d. a Other Corr eSpOnd 1e random motion. occures for both nadir and 
IFOV were generated. With these numbers, backward viewings, MIF degradations 
image motion was added to the original s 
: 2) Stereo Matching Error 
SPOT/HRV image with FFT/IFFT rpocesses (2) in order to ne CIT ani-effect of MIF 
in pitch direction. Thus MTF degraded : 
images: were simulated. A portion of desradation on stereo matching error, 
simulated image is shown in figure 3. the following SPOT/HRV panchromatic data 
With these images, cross correlation of stereo pair is used. ; 
between image chips, matching accuracy the 812 À 400 panel Jere genre tag in 
and DEM estimation accuracy were pair. itnin. a. subset o 
investigated assuming the same image stereo pair, 9 tip images which consists betwee 
motion is existing on both optics for of 32 X 32 pixels were extracted. MTF of assess 
stereo imaging system. the tip images was degraded by using for 9 
spatial filtering then cross correlation " 
corre 
Was : 
match: 
a = rms motion correi 
-in an exposure 
interval Was as 
9 tir 
pair. 
$ 
= 
= 
0 0.5 1.0 
NORMAL IZED SPATIAL FREQUENCY, K,(1/a) 
Fig. 1 Attitude jitter is random(Normal distribution) image 
motion within an exposure time, MTF of the imaging system 
is degraded 
Modulation Transfer Functions(MTFs) for image motion 
(normalized to a spatial frequency KO = 1/a where a = rms motion 
in an exposure interval). 
992