The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008
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The MTF value of PAN at nyquist frequency is 8% in the
KOMPSAT-2 specification. The beginning MTF value was less
than 8% (~ 6%) (Figure 12), so that we has analyzed the factors
of the KOMPSAT-2 MTF; AOCS stability & bias, noise, TDI
line rate error and Yaw steering error.
Figure 13. The analysis result of TDI line rate and Yaw steering
for MTF
FWHM = 25373 Pixel]
Figure 15. Non-symmetry of the KOMPSAT-2 PSF
Figure 16. PSF from the Night images
The optimal PSF could be measured from nine Night lamp
images (Figure 17, Right), and then the MTF kernel (Figure 18)
has been generated by the Wiener filter (Figure 17, Left). The
size of the generated MTF kernel is 13 x 13.
Figure 14. The MTF value from the Night lamp
In Figure 13, we have found out the effect of the TDI line rate
could be neglected, but the Yaw steering value was higher than
the KOMPSAT-2 specification (0.05 deg). After KARI AOCS
team uploaded the AOCS calibration data included with the
Yaw steering offset at Feb 14, 2007, the MTF value of
KOMPSAT-2 image data was measured again with the image
from the Night lamp (Figure 14), and then we got the around
‘7%’ of the MTF value.
3,2 MTF Compensation (Correction)
We have studied the difference between ‘7%’ from the Night
lamp and ‘8%’ from the KOMPSAT-2 specification, and then
the reason of it;
Non-symmetry of the KOMPSAT-2 MTF curve (Figure 15)
Non-linearity in less than 200 DN
This difference can be compensated by MTFC, so that the
optimal Point Spread Function (PSF) for the KOMPSAT-2
image data has to be needed for it.
Figure 17. Left: Wiener filter to generate the MTF kernel,
Right: MTF kernel (13x13) for MTFC
Figure 18. Left: Raw image data, Right: MTFC image data
The KOMPSAT-2 IRPE has a framelet wavelet de-convolution
algorithm (Jeong) for the MTFC and the de-noising. In Figure
18, MTFC image data is better quality than raw one. The MTF
value of the MTFC image data is 11 ~ 12 %. But, there is a
minor problem of it; aliasing.
