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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
characterized by several absorption bands of CO2. The existing 
atmospheric correction method to removed atmospheric 
absorptions is to use empirical transmission functions based on 
the ratio of two spectra acquired at the top and base of the 
Olympus Mons scaled to the CO2 absorption depth at 2 pm 
(Bibring, J.P., et al., 1989; Maustard, J.F. et al. 2005). 
3.2 Minimum Noise Fraction 
The atmospherically corrected image was then further 
processed using a called minimum noise fraction (MNF) 
transformation method. Figure 1 illustrates the atmospherically 
corrected I/F images and the MNF resulting images in the 
Maridiani Planum area. It is clear that the albedo image (Figure 
lb) reflects very similar information as the true color image 
(Figure la). The most interesting thing found is that the MNF 
band 1 (Figure lc) is almost identical with the albedo image, 
while other bands are very different from the albedo image. 
This is consistent with the scatter plots and correlation 
coefficients shown in Figure 2: very good correlation 
coefficient (r = 0.988) between the albedo image and the MNF 
band 1, no correlation between albedo image and other bands. 
Figure 1. Atmospherically corrected I/F images (OMEGA 
image ID ORB0529 3, Meridiani Planum region) and MNF 
resulting images: a: The true-color composition image (bands 
0.66, 0.55, and 0.47 pm); b: Albedo (sum of reflectance of 114 
bands from 0.969 to 2.553 pm); c, d, e, f are images of MNF 
bands 1, 2, 3, and 4, respectively. 
The first six MNF bands of the ORB548 3 at the Ophir-Candor 
Chasma area account for about 77 % of information from all 
114 bands (0.926 to 2.55 pm) together. In particular, the MNF 
band 1 (Figure 3) accounts for ~47 % of total information and 
has an inverse relation with the albedo image (r = - 0.91), 
differing from Maridiani Planum image. Due to dramatically 
changing of the topography in this area, the MNF band 2, which 
accounts for 21% of total information, represents the terrain 
information. The bands 2, 3, 4 together account for ~27% of 
total information and contain most of geological unit 
information. A false color image of MNF band 432 composite 
can be produced to delineate the lithologic units. 
2 
LL. 
H 
5 
40 
0 10 20 30 
Sum of 114 bands 
20 
0 10 20 30 
Sum of 114 bands 
Figure 2. Scatter plots between albedo (sum of reflectance of 
114 bands) and MNF bands 1, 2, 3, and 4, respectively (data 
from Figure 1), with r as the correlation coefficient of two 
variables. 
sum of 114 bands reversed MNF b1 MNFbl 
Figure 3. Atmospherically corrected I/F images (ORB548 3, 
part of the Ophir-Candor Chasma) and MNF resulting images: 
left: Albedo image (sum of reflectance of 114 bands); middle: 
reversed MNF band 1; right: MNF band 1. 
So tjjg MNF band 1 is mostly correlated (positively or 
negatively) to'the albedo ( r up to 0.83 - 0.98) of the OMEGA 
imagery, while the MNF bands 2, 3, and 4 contained almost 
lithologies information for making an informative and useful 
geologic unit map. A false color image of MNF bands 2, 3, 4 
could then be produced to represent major geological 
information for the delineation of lithologic units. 
3.3 Lithologic unit delineation 
Based on the false color image generated from above method, 
the lithologic units could be delineated by distinct tonal 
difference. These unit can also be reference to and compared 
with existing Martian “geologic units” based on geomorphology, 
crater features and density, albedo, multi-spectral properties, 
and thermal characteristics (USGS. 1986 and 1987, Arvidson, R. 
E., et al. 2003). 
3.4 Spectral matching 
Representative spectrum of these units was then processed to 
match with various mineral and rock standard spectral libraries