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
2 a
E 40. 5 401 V
$ B lv
20.\X 20: lta
A
0 Tm À Q T
0 32 64 96 128 32 64 96 128
WAVE NUMBER WAVE NUMBER
BAaND-4 1j BAND-4
cn
ce
1
POWER (DB)
Fm
e
v
RO entr
T T T 1 0 T T T 1
32 64 96 128 0 32 64 96 128
WAVE NUMBER WAVE NUMBER
!
m
ea
(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