The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
Figure 1. Affection of different frequency jitter on imaging 
process, where (a) represents high frequency jitter with t > T, (b) 
represents low frequency jitter when t < T 
2.2 Affections of Jitter with Different Directions 
Satellite jitter can be separated into three directions, along optic 
axis, along track and across track. Here image quality affections 
of jitter in different directions are discussed. 
3. PROPERTIES OF BEIJING-1 SMALL SATELLITE 
JITTER 
To facilitate exploration of jitter characteristics, data employed 
in our research is the Level 1 product with radiometric 
correction done. 
In Beijing-1 small satellite images, jitter performs as jagged 
edges, period of the jag is about 8 to 9 lines, the frequency 
approximates 200 HZ. Period of the jitter is not only larger than 
pixel integration time, but also larger than line integration time. 
It is low frequency jitter. In visual observation, the jagged edges 
mainly express the devastating across track jitter, the jitter can 
be assumed as similar linear movement of pixels on the whole 
line, which causes displacements of pixels to their original 
positions and lead to jagged edges and linear objects shown in 
the image. As period of jitter is far larger than pixel integration 
time, displacements of pixels on the same line can be taken as 
one value. 
To prove applicability of the above assumptions in jitter 
removal process, the model is testified with Beijing-1 
panchromatic image containing linear objects to see if jitter 
performance in the image does conform to the hypothesis. As 
jitter shows clearly on linear objects and edges, the runway 
from an airdrome is chosen to evaluate property of the jitter. 
Properties obtained from an airdome are taken as reference for 
correction of the whole line. 
When the jitter is along optical axis, change of the blur circle 
diameter d can be expressed as 
d= 21 (i) 
H-f-a 
Where/= focal length 
H = height of the orbit 
a = swing of the jitter wave 
D = aperture of the camera 
For jitter along track, the equation is as follows. 
d ~c J rvt~c + 
f 
H 774 
X 
(2) 
Where v = motion speed of the imaged objects. Jitter in along 
track direction mainly changes v value and disturbs the imaging 
process. 
For the fact that in satellite imaging process, H is far larger than 
f the change of d is inapparent, along optical axis and along 
track jitter has little impact on quality of the acquired images. 
Jitter across track causes diameter expansion of the blur circle, 
if swing of the jitter is large to some extent, pointing object of 
the CCD sensor will change and cause geometric errors in 
imaging process. Affection of across track jitter can be 
devastating and is the most remarkable. 
The process is as follows. First, the jittered runway is 
segmented using proper threshold, then DN centroid of the 
segmentation result is calculated as central position of the 
runway, after that, linear regression is done with x y value of 
the central position and residual value is calculated. 
The runway can be restored to be linear by taking the residual 
as displacement value in horizontal shifting of relevant lines. 
With applying the displacement value to shifting and sampling 
of whole lines of the image, jitter that affiliates to all linear 
objects and edges are removed (Figure 2). Therefore it can be 
confirmed that the assumption of the jitter in Beijing-1 
panchromatic image as uniform displacement of pixels on lines 
(b) 
Figure 2. Jitter evaluation with image of an airdrome, where (a) 
represents the jittered image, (b) represents the image after 
shifting and sampling of whole lines