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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
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impervious area 
bare soil 
Figure 4 Normalized spectral profile of endmembers extracted from pre-C corrected(left) and post-C corrected (right)ASTER 
imagery in test site. 
4. RESULTS AND DISCUSSION 
4.1 Comparison analysis 
In mountain area, the terrain undulation effect which could 
cause shadow or occlusion is not ignored, shadows frequently 
occur in airborne or space-bome imagery in terrain area with 
steep slope when the sun elevation angle is low. A number of 
technologies were developed to circumvent the terrain 
illumination effect, here we selected the C correction method, 
Fig2 shows the pre-corrected and post-corrected ASTER images 
(bandsl32 for RGB)of test site. To visually compare the two 
images same histogram stretch was applied to them and the 
histogram of C corrected image was matched to the 
pre-corrected one. As can be seen from Fig2, Fig2(a) had a lot 
of shadows, the terrain undulation and stereo was apparent 
across the scene(except the urban area), whereas Fig2(b) which 
was C corrected had less shadow and the terrain undulation was 
also inconspicuous. Fig2(b) was even more smooth than Fig2(b). 
therefore it showed that the terrain undulation impact in study 
site could be dramatically reduced by C method employed 
above. 
The spectra profile along a random line(Fig3) across undulate 
area within test site showed that the spectrum variance of 
objects which were similar in spectra value but locate in both 
sunny side and opposite side due to the terrain undulation was 
diminished(Fig3(b)). So the C correction could also effectively 
reduce the phenomenon characterized by that same targets 
display varying spectral radiance due to the topographic 
undulation. 
4.2 Regression and validation the C method 
LSMM was applied to both pre-corrected and post-corrected 
ASTER data of study site and two vegetation abundance 
images were calculated. Unfortunately we did not collect the in 
situ vegetation abundance data when the ASTER image was 
acquired. But literatures showed that the vegetation abundance 
and normalized difference vegetation index-NDVI or modified 
vegetation index-MVI have close correlation(Carlson et 
al,1997;Qi et al,2000;Zeng et al,2000 McDaniel and Haas, 1982), 
the correlation coefficient could indicate the unmixing precision 
at a certain extent. In addition, our main objective is to 
investigate the impact on LSMM due to the topographic 
undulation while not to specifically evaluate the precision for 
unmixing the vegetation abundance, so the correlation 
regression method is alternatively feasible for characterizing the 
negative effect of terrain undulation in this study. 
Normalized difference vegetation index and modified 
vegetation index(MVI) or transformed vegetation index(TVI) 
maps were derived from pre-corrected ASTER image as 
follows: 
NDVI=( R-NIR-Rred)/( RNIR-Rred) (7) 
AM(TVI) =yj( RMR-Rredy( RMR-Rred)+0.5 (8) 
Where R nir and R red are the spectral reflectances in ASTER 
near-infrared(band 4) and red(band 3)bands; 
To apply regression analysis 5,000 sample points were selected 
randomly in four images including NDVI, MVI, vegetation 
abundances from pre-C corrected and pos-C corrected ASTER 
images. Sequentially the multi-regression analysis between 
vegetation abundances and vegetation indexes(NDVI and MVI) 
was employed and the results were displayed in Fig5. 
Correlation coefficient (R)or square-R as a indicator index was 
chosen to quantitate the unmixing precision indirectly. It should 
be noted that a high R 2 value could indicate the good unmixing 
precision and also the effectiveness of C correction. As is 
shown in Fig5 the R 2 between vegetation abundances and 
vegetation indexes followed by C correction is higher than that 
of pre-corrected ones. The unmixing precision was improved 
17.6% and 18.6% in R 2 value for NDVI and MVI by 
minimizing or even removing terrain undulation effect using C 
correction method. On one hand, it proved that, the terrain