The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
In Unit-3, two major representative spectra were identified: 3- 
yellow and 3-green. The best matched lithologies are basaltic 
andesite for 3-yellow and basalt for 3-green. The possible 
minerals matched are hematite for 3-yellow and pyroxene, 
hematite, and monticellite for 3-green. The Unit-3 consists of 
well developed basaltic sediments named as etched terrain and 
layered terrain (Hynek, et al, 2002) that, together with the Unit- 
2, overlies the oldest dissected crater terrain (DCT) unit and 
partly covered by hematite-bearing soil or dune (Arvidson, et al, 
2003). They may originate from the erosion of the south 
highlands (Edgett, 2005). Although the unit-4 shows variable 
colors from pink to green, the two major representative spectra 
(4-green and 4-pink) best match with basalt. Possible minerals 
matched are copiapite, hematite and pyroxene. Copiapite is a 
poly-hydrated sulfate mineral and was also found in an area of 
the etched terrain (Unit-3), just east of this OMEGA image 
(Gendrin et al., 2005). The unit-4 corresponds to the mantled 
terrain that mantled by tens of meters of aeolian deposits 
(Arvidson et al., 2003). 
4.2. Ophir-Candor Chasma area 
Ophir-Candor Chasma area is the widest portion of the Valles 
Mariner and the biggest canyon on Mars. A false color image of 
MNF band 4, 3 and 2 composite can be produced to delineate 
the geologic units. As a result, Ophir-Candor Chasmas area can 
be divided into 3 geologic units (Figure 5a) and the 
representative spectrum of each unit is shown on the Figure 5b. 
Figure 5c is the USGS “geologic” unit map, in which 9 
different units were mapped (relative or estimated ages also 
indicated in the map). The best matched lithologies for each 
unit are shown in Table 2, while best matched minerals are 
listed as reference only. More details described as follows. 
WaoWHiffiHh 
Figure 5. a. Geologic unit map (3 units) based on false-color 
image of MNF band 4, 3, and 2 of ORB548 3 at the Ophir- 
Candor Chasma area; b: Representative unit spectrum 
corresponding to the units and colors in the left image, by 
averaging the spectra within the square area of each unit, c: 
USGS “geologic” map of the same area: colors and numbers on 
the legend are 1-Ridged Plains Material; 2-Older Channel 
Material; 3-Undivided Material of Highly Deformed Terrain; 4- 
Silde Material; 5-Layered Member; 6-Smooth Unit; 7-Floor 
Member; 8-Subdued Cratered Unit; 9-Yonger Fractured 
Material. Numbers in the “geologic” map are relative or 
estimated age (0.1 Ga) of the geologic units. 
The Unit-I, at the chasmas floor with low albedo (Figure 3) and 
colored yellow in Figure 5a, best matches with mafic basalt. 
Possible minerals are pyroxene and hematite. Typical ferrous 
absorptions (such as 1.04 pm) and broad pyroxene absorption at 
2.0 to- 2.4 pm implicated that the low albedo areas in the 
Chasma floor is mainly basaltic materials that possibly have 
large basaltic bedrock exposure (Bibring et al., 2001). 
Polyhydrated sulfate was also mapped in some small areas of 
the Chasmas floor (Gendrin, et al., 2005). Unit- I is well 
corresponding to Floor Member (7) and Older Channel Material 
(2) in the USGS geologic map (Figure 5c). Some parts of the 
Layered Member (5) in the USGS map are also part of the Unit- 
I. 
Unit 
MNF 
b432 
Lithologic spectral matching 
Minerals spectral matching 
Lithologic 
SFF 
SAM 
Minerals 
SFF 
SAM 
Unit- 
1 
1-yellow 
Basalt-cdrs83 
0.87 
0.96 
Pyroxene-ccrs85 
0.85 
0.96 
Hematite-cjb496 
0.78 
0.94 
Unit- 
2 
2-green 
( Pink) 
Basaltic andesite 
0.80 
0.97 
Copiapite-gds21 
0.93 
0.34 
Hematite-lahe03 
0.90 
0.85 
3-blue 
Basaltic andesite 
0.83 
0.95 
Flematite-lahe03 
0.88 
0.95 
Hematite-cdrh07 
0.84 
0.95 
4-cyan 
Basaltic andesite 
0.81 
0.97 
Copiapite-gds21 
0.93 
0.29 
Flematite-clcyl 1 
0.92 
0.84 
Unit- 
3 
5-red 
Basalt-cars83 
0.85 
0.98 
Kieserite 
0.90 
0.37 
Flematite-lahe03 
0.87 
0.97 
Table 2. The spectral matching score of lithologic unit of 
ORB0548 3 at Ophir-Candor Chasma area 
The Unit-n includes three sub-units: green (and pink) areas (FI- 
green) at the cliff edge (corresponding to Undivided Material of 
Highly Deformed Terrain (3) and Yonger Fractured Material (9) 
in the USGS map), blue or dark blue areas (n-blue) at the 
northern of Ophir Chasma (Slide Materials (4) of the USGS 
map), and cyan areas (n-cyan) at the top of planum 
(corresponding to Ridged Plains Material (1), Smooth Unit (6), 
and Subdued Cratered Unit (8) in the USGS map). All of them 
best match with the basaltic andesite. This means that they are 
actually the same geologic units: n-green is actually the cliff 
edge of the n-cyan, while n-blue is just the slide materials from 
the cliff edge of the planum (n-cyan). The color differences of 
this same unit are the combined effect of topography, terrain 
texture and solar illumination. The topographic difference is 
huge in this area, i.e. the elevation of the flat (planum) area (n- 
cyan) is about 3.5 - 4 km, while the elevation of slide materials 
(n-blue) changes from -3.8 - -4.5 km. Best matched possible 
minerals are hematite and copiapite, though the SAM scores for 
copiapite are very low (only 0.29-0.34 in Table 2). 
The Unit-Ill colored red or dark red, corresponding to the 
Layered Member (5) in the USGS map, though the Unit- HI 
consists of several isolated small areas compared with the large 
area of the unit 5 in the USGS map. Most part of the unit 5 
actually belongs to the Unit-I in our delineation. The possible 
minerals are kieserite and hematite. But the kieserite does not 
get a high score (only 0.37) in the SAM method, though the 
best score from the SFF method. Gendrin et al. (2005) found 
wide distribution of kieserite and polyhydrated sulfate in the 
Unit area. 
5. CONCLUSION 
A four-step procedure are developed to delineate the geologic 
unit map using the ESA’s OMGEA/Mars Express data and 
proved the method to be efficient. Two areas (Meridiani 
Planum and Ophir-Candor Chasma) were chosen to test the 
methods, some good results have been achieved by compared 
with previously well-known rock and mineral compositions 
derived from TES, THEMIS, and Opportunity Rover as well as