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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
the USGS “geologic” unit map. The minimum noise fraction 
(MNF) method is an efficient method to derive noise-free 
principle components that can be used to delineate the Martian 
geologic units. It is found that the MNF band 1 is mostly related 
(positively or negatively) to the albedo (r up to 0.83 - 0.98) of 
the hyperspectral imagery, while the MNF bands 2, 3, and 4 
contained almost all lithologies information for making an 
informative and useful geologic unit map. 
The two spectral matching methods (spectral feature fitting and 
spectral angle mapper) have different performances in matching 
lithologies and minerals. The SFF method especially 
emphasizes the overall similarity of positions and depths of 
absorption bands for two spectral curves, while the SAM 
method emphasizes the overall similarity of the two spectral 
curves and does not care much about the position and depth of 
absorption bands. Three good examples found in this study are 
seen in the Table 2, in which the copiapite and kieserite have 
the highest SFF scores (0.90 - 0.93), while the SAM matching 
scores for them are very low (0.29 - 0.37). This suggests that 
the existence of those two minerals are questionable, even 
kieserite was reported in the region by the Gendrin et al. (2005). 
But another explanation for the difference is that as mentioned 
in,the method section, the unit spectrum used in the study is 
actually the spectral average of a small area. So the unit 
spectrum is extremely mixed spectral signature which might 
good for lithologic unit mapping but not for individual mineral 
identification. So the minerals matched using this method are 
only for reference only. This also explains that the Unit-2 of 
Maridiani Planum area, best matched mineral is not hematite, 
but hematite was found widely distributed in the area by the 
TES and Opportunity Rover. Overall, the two matching 
methods (SFF and SAM) complement each other and should be 
always used together. If both give a high score, the matching 
results should be much confident than only one high matching 
score. 
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ACKNOWLEDGEMENTS 
The authors would like to thank Yves Langevin, John Mustard, 
Joe Zender, and Aline Gendrin for their directions on the 
OMEGA data pre-processing and atmospheric corrections. 
Special thanks also go to ESA and OMEGA/Mars Express 
Science team for acquiring data and making data available to 
rest of the world. The first author would like to thank the 
Chinese State Scholarship Fund Award (2005-2006) to him to 
make this collaborative study possible. The project is supported 
by NSFC program “OMEGA/Mars Express Surface Spectra 
Retrieve Methods and Mineral Detection (40772200) ”