Full text: XVIIIth Congress (Part B2)

f illustrates the results for a 3-look ERS-1 SAR image. 
The results coincide with the theoretical analysis. 
) However, the speckle index changes with the intensity 
of the image. The lighter the image is, the smaller the 
speckle index is. From this result, we indicate that the a 
linear fit is not accurate enough. 
] Probability density function(pdf) of SAR images: In 
Xx] section 2, the statistical models of the SAR images are 
] provided to have a Gamma distribution. Here we 
process a patch of homogeneous area in the ERS-1 and 
] ERS-2 image to test the distribution of the SAR images. 
" The tested results is shown in Fig.2,(a),(b). Fig.2(a) 
7 shows the pdf of a ERS-1 single-look image and 
7 Fig2.(b) shows the pdf of a ERS-2 single-look image. 
] The results accord with the Gamma distribution. The 
{A slight deviation is due to the heterogeneous effect. 
Distribution of ERS—1 Amplitude Rage 
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Quad Fig.2 (a). pdf of a ERS-1 single-look image 
700 
(b).pdf of a ERS-2 single-look image 
Pdf of speckle index: It demonstrates the variation of 
speckle index for any one SAR image and illustrates 
the characteristics of a heterogeneous image. Fig.3(a) 
he shows the pdf of speckle index for an ERS-1 image. 
le- Several curves are overlapped in this figure to show 
ne that the speckle index is changing with the variation of 
I the terrain. The pdf of speckle index can be 
its approximated as the Gaussian distribution for the 
D homogeneous area. However, for the heterogeneous 
C 
167 
area, the pdf of speckle index is a complicated function 
and needs to be investigated (Ref. Fig.3 (b)). 
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Fig.3 (a) the pdf of speckle index for different areas 
(b) the pdf of speckle index for a heterogeneous area 
4. Evaluation of Filtering Techniques 
Both quantitative evaluation and qualitative evaluation 
have been made to evaluate the filtering techniques for 
ERS-1&2 imagery. 
Quantitative Evaluation: 
The performance of evaluating eight filters for 3-look 
ERS-1 images by computing the mean value, standard 
deviation and speckle index is shown in table 2. The 
window size of filtering is 7 by 7. The pixel number for 
statistical value is 400. The testing was done in a HP 
workstation using the PCI software package. From the 
average statistical data, the Box Filter, Frost Filter, Lee 
Filter, and Kuan filter have a good performance to keep 
the mean value of the tested area. Median Filter, 
Enhanced Lee Filter, Enhanced Frost Filter and GMAP 
Filter make a small amount of change in the mean 
value. Box filter is the best one to reduce speckle noise 
for SAR images. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996 
 
	        
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