Full text: XVth ISPRS Congress (Part A2)

  
  
  
  
  
  
  
  
  
564 
(4) Coherent Noise Analysis 
In MSS image of Landsat 4, coherent noise exists in a low-level uniform 
area such as sea surface. Investigation was made to see whether the same 
phenomenon is found in TM image or not by Fourier analysis. Data used in 
the analysis were (a) Detroit, July 25, 82 and (b) Chicago, Oct 25, 82. In 
the analysis, ocean areas with 256 x 256 pixel size were selected as test 
sites and applied with Fourier transform. In Fig. 8 shown are raw image, 
its Fourier spectrum image, pixel direction (horizontal) Fourier spectrum 
and line direction (vertical) Fourier spectrum. 
As shown in (a), coherent noise component with a wave number of 17.8 
(wavelength 14.3 pixel) is oberved in pixel direction. While in Fig. 8.(b), 
another coherent noise component with a wave number of 77 (wavelength 3.3 
pixel) appears. In both scenes, the same frequency components existed in 
all bands. The magnitudes of the first and second coherent noise components 
are 0.5 level (p-p) and 0.2 level (p-p), respectively. On the other hand, 
in the line direction (vertical) Fourier spectrum, frequency components with 
wave numbers of 8 and 16 (wavelength 32 and 16 pixels) exist, which are due 
to "striping" (intra-detector responsivity difference) and "banding" (intra-scan 
radiance difference) in the image. 
  
  
  
  
  
  
  
4 80. 
80 BRND-4 — BAND-4 
— 604 ~ 807 
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(bj Chicago, Oct 25, '82 
Fig. 8 TM Fourier spectrum analysis (Band 4) 
from left: raw image, two-dimensional Fourier spectrum image, 
pixel-direction Fourier spectrum, line-direction 
Fourier spectrum
	        
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