International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
Syr Darya deposits are enriched in gypsum, aragonite and
calcite. Diatoms are hardly observed. On the contrary, the Amu
Darya sediments are characterized by aragonite and Mg-calcite
precipitation and high Fe and Mn carbonate contents (Le
Callonnec).
If the geochemical characteristics of Amu Daria sediments have
not changed from Pliocene to Holocene era, then is reasonable
to expect high Fe contents in Red Series of Cheleken Peninsula,
which are formed by Pliocene-aged Paleo Amu Darya
sediments.
The use of ASTER band 1 / band 2 can be affected by band 2
(660 nm) absorption feature which is caused most likely by
chlorophyle and other pigments contained in green vegetation
(Mather, 1999). This fact has been ignored in this study,
because the vegetation mapping based on NDVI has shown no
or sparse vegetation cover in the areas which in spite of it
shows band 2 absorption feature (presence of chlorophyle). The
spatial distribution of band 2 absorption is not linked with
NDVI values and band 2 / band 1 ratio values. In other words, if
exists any sparse vegetation cover (exhibited by band 2
absorption), it should not affect the conclusion that Red Series
can be mapped by ASTER band 1/ band 2 ratio. This problem
can be solved by purchasing other VNIR data of the study area
(as Landsat ETM+ or SPOT), which can give additional
information.
[4
+
Yo
Figure 5. ASTER band 1/ band 2 ratio image shows ability to
map outcrops of Red series, which have the lowest values of
ratio in the area (the lowest values appear in blue, the highest
appear red), compare with Figure 4.
ASTER SWIR band rationing to map major mineral
groups. Ratio images designed to display the spectral contrast
of specific absorption features have been used extensively in
geologic remote sensing and Rowan, 2003 has already applied
this remote sensing technique on ASTER data to carry out
lithologic mapping in the Mountain Pass, California area.
Relative absorption depth (RBD) images are an especially
useful three-point ratio formulation for displaying Al-O-H, Mg-
O-H and CaCO, absorption intensities prior to conducting more
detailed, time-consuming spectral analysis. For each absorption
feature, the numerator is the sum of the bands representing the
shoulders (bands 1 and 2), and the denominator is the band
located nearest the absorption feature minimum (band 3);
removal of continuum increases the intensity of the absorption
feature:
RBD = (band 1 + band 2) / band 3 (1)
Several different RBD images have been created. The ((band 7
+ band 9)/band 8) RBD image which highlights the CaCO; and
Mg-O-H absorption feature at 2237.5 nm is affected by higher
values of band 9 caused by ASTER SWIR instrument problem
(Scholte, 2003), thus the presence of absorption feature occurs
across whole studied area, with exception of pixels located
along NW coast, where sharp fall-off of spectra from band 8
towards band 9 overestimate the higher values of band 9.
In order to eliminate the effect of band 9, the threshold value
has been changed to get more presumable result. First is
possible to state, the presence of absorption feature is linked
with brine activity, the other areas which most likely contain
CaCO; bearing minerals are roads in Cheleken City and on
some other places of peninsula. The presence of the band 8
absorption feature differ two areas classified as dunes. Whereas
the bright dunes (G) show absorption feature at 2237.5 nm
(even without correction of band 9), the dunes close to the north
sand bar has some absorption at this wavelength. These dunes
have other spectral characteristic then other dunes in the area
(more Calcite like then Alunite).
The Al-O-H absorption RBD image ((band 5 + band 7))/band 6)
shows that this absorption feature is in general distributed in
areas of brines activity, but highly significant is that brines in
NE part of Chochrak Ridge does not show presence of Al-O-H
groups (and thus can be easily differentiated from the other
brines). As other meaningful fact appears that large areas in the
SE part of the scene shows presence of Al-O-H Mica absorption
as well, but more detailed look at the spectra shows that these
areas have broad absorption feature both in Al-O-H Mica and
AI-O-H Phyrophillite group. The presence of AI-O-H Mica
absorption feature could be caused by stronger brine activity in
the past.
The largest areas are covered by Al-O-H Alunite &
Phyrophyllite absorption RBD image which occurs on most
areas. Generally the pixels belong either to AI-O-H Alunite or
to Al-O-H Mica group.
The ((band 5 + band 9)/band 8)) RBD image successfully maps
distribution of pixels dominated by deep absorption at 2237.5
nm, which are linked with brine activity located in NE part of
Cheleken. The spectra of other brine ponds mapped by this
band ratio show both dominating 2237.5 nm absorption and less
distinct absorption feature caused by Al-O-H Mica group.
Figure 6. ASTER SWIR band ratio highlighting strong
absorption feature at 2237.5 nm (probably carbonates and Mg-
O-H group).
2.5 Spectral methods
Spectral signatures of minerals in SWIR. Several spectra of
minerals from USGS Spectral library have been resampled to
demonstrate major spectral signatures of minerals in SWIR.
Minerals characterized by absorption feature near 2165 nm
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