The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008
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from USGS, John Hopkins University, and Brown University.
Two spectral matching methods, spectral angle mapper (SAM)
(Kruse et al. 1993) and spectral feature fitting (SFF) (Clark et al.
1990), were applied based on both spectra and/or continuum
removed spectra for scoring each individual minerals and
lithological classes from libraries with individual representative
spectrum of each unit.
The highest scores of matched minerals and lithological units
were then recorded for each unit. It should be realized that the
representative spectrum, an average spectrum of an area, may
well represent the lithologic information for the area but not the
mineral information for the area due to extremely mixing
feature. So matched minerals recorded here are only for
reference purposes.
4. EXPERIMENT RESULTS
4.1 Maridiani Planum area
The Maridiani Planum area is the Opportunity Rover landing
site and has been studied in a great detail (i.e., Arvidson et al,
2003; Christensen et al. 2001; Squyer, et al, 2004). Figure 4a is
the RGB composition of MNF bands 4, 3, and 2, showing four
major geologic units in the region. Figure 4b shows the
representative spectra (atmospheric corrected I/F) for each unit
(unit number and color corresponding to the number and color
in Figure 4a). Figure 4c is the geologic unit map based on
morphology, topography, and hematite index (Arvidson et al,
2003), with the red frame area representing the footprint of the
ORB0529-3 image (Figure 4a). In comparison of the geologic
units mapped by the OMEGA false-color image and those from
Arvidson et al. (2003), it is clear that they matched very well.
Unit-1 (in Figure 4a) corresponds to unit DCT (in Figure 4c)
named Noachian dissected cratered terrain. Unit-2 corresponds
to unit Ph named hematite-bearing plains deposit. Unit-3
corresponds to etched terrain unit E and unit P. Unit-4
corresponds to unit MCT named aeolian deposits mantled
terrain.
Figure 4. a: Geologic unit map (4 units) based on RGB image
of MNF band 4, 3 and 2 of Figure 1. 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:
“Geologic unit” map from Arvidson et al. (2003), with the red
frame representing the footprint of ORB0529-3 [DCT:
Noachian dissected cratered terrain; Ph: Hematite-bearing plain
deposit that transitions to unit P; E: Etched terrain; MCT:
Aeolian deposits mantled terrain].
Except for the unit Ph well-known as hematite-bearing plains
(Christensen et al. 2001), there was no way to tell minerals and
rock compositions for other units by using traditional
topography, morphology, and albedo-based datasets. With
spectral matching, it is possible to estimate the dominant
minerals with hyperspectral data. Table 1 lists the spectral
matching scores for each unit spectrum shown in Figure 4b as
to the best possible lithologic (and mineral types as reference
only), based on spectral feature fitting (SFF) and spectral angle
mapper (SAM) methods.
unit
MNF
Lithologic matching
Minerals spectral matching
b432
Lithologic
SFF
SAM
Minerals
SFF
SAM
Unit
1 -Cyan
Diabase-hl
0.89
0.98
Pyroxene-cldd8
0.89
0.86
-1
Basalt-cdrs83
0.89
0.91
Pigeonite
0.88
0.86
Unit
-2
Basalt-h5
0.90
0.88
Geothite ws220
0.91
0.76
2-Red
Basalt-c 1 rb34
0.91
0.82
Limonite hs41
0.91
0.63
Ferrihydrite
0.91
0.64
3-yellow
Basaltic
0.82
0.97
Hematite-cjb496
0.90
0.95
Unit
-3
andesite
Flematite-lahe03
0.90
0.94
Pyroxene-cldd6
0.92
0.75
3-green
Basalt-cers83
0.90
0.96
Flematite-cjb496
0.91
0.95
Monticellite
0.89
0.98
Hematite-cjb496
0.90
0.95
4-Green
Basalt-cers83
0.88
0.98
Monticellite
0.89
0.96
Unit
Pyroxene-ccrs85
0.86
0.94
Copiapite-gds21
0.93
0.29
4-pink
Basalt-cdrs83
0.85
0.98
Pyroxene-
clsb58
0.91
0.76
Hematite-cjb496
0.89
0.95
Table 1. The spectral matching score for each lithologic unit of
OMEGA image (ORB0529 3) at Meridiani Planum
The Unit-1 colored as cyan, located in the most-southern
portion of the OMEGA image, is distinct from the Unit-2
colored as dark-red. Both units are dark in the true-color, albedo,
and MNF band 1 images (Figure 1) due to the same low albedo
characteristics. However, the Unit-1, named as Crater Unit and
Dissected Unit of Plateau Sequence in the USGS “geologic”
maps, best matches with mafic basalt, possible diabase and
minerals of pyroxene and pigeonite as reference (Table 1).
While the Unit-2, including the Opportunity landing site, best
matches with basaltic rock and possible minerals of goethite,
limonite and ferrihydrite, hydrated iron oxide minerals. These
mineral types differ from the TES results (Christensen et al.
2001; Hynek, 2004) in which hematite, non-hydrated iron oxide
mineral, was found rich in this unit. The major reason as
mentioned earlier is that the representative spectrum got here is
extremely mixed and barely tell individual minerals, but do give
some hint about the compositions here. For example, all
possible minerals seem to be iron-oxide minerals. In addition,
the Opportunity’s multispectral images show a stronger kink
spectra near 530 nm and a shallow absorption near 900 - 950
nm, indicating the possible existence of ferrihydrite and
goethite (Bell et al. 2004). The weak absorption near 900-950
nm is consistent with the presence of fine-grained, crystalline
hematite alone (Bell et al. 2004). However, if the presence of
goethite is true, it would support that the hematite formed in
watery conditions, since the goethite only forms in the presence
of water (liquid, ice or gaseous form), while hematite usually,
but not always, forms in the presence of water. The
Opportunity’s other instruments suggested that the soil consists
of fine-grained basaltic sand and hematite-rich spherules and
that the finely laminated rocks, siliciclastic sediments, contain
abundant sulfate salts with embedded hematite-rich spherules
(Squyer, et al, 2004).
