Models MASTER P-value |Correlation |R’
RX = 79,4678 -0,579643*Alunite [0.0004 |-0.811637 65.88%
RX = 69,1488 - 0,50982*IIlite 0.0001 |-0.855083 73.12%
RX = 126,893-0,905153*Kaolinite 10.0178 |-0.620723 ]38.53%
Table 2. Comparison of relationships between spectral
anomalies and hydrothermal alteration, from MASTER images.
Among all linear models obtained, the one which shows a
higher R-squared value (73.12%), corresponds to the RX-Illite
from MASTER data.
The P value obtained less than 0.05 in all cases, except for RX-
kaolinite, RX-montmorollonita from HyMAP, indicates that
there is a statistically significant relationship and there is no
indication of serial autocorrelation in the residuals at the level
of confidence 95.0%.
The R-squared statistic indicates that the adjusted models
explain the variability in different percentages between
hydrothermal alterations and spectral anomalies. The maximum
correlation coefficients (-0.831632 and 0.850365) indicate a
moderately strong relationship between the corresponding
variables.
Figure 4. Detail of RX spectral anomalies (a), Alunite (b)
and Illite (c), from 2005 HyMAP image in Turrialba crater
(top). Detail RX spectral anomalies (a), Alunite (b) and Illite
(c), from 2005 MASTER image on manmade cover (lower).
There is correlation, positive or negative depending on the case,
between hydrothermal alteration detected and spectral
anomalies calculated from HyMAP reflective channels.
In the case of thermal anomalies, this relationship is not as
consistent as the previous ones. However, this relationship is
showed with biophysical parameters calculated and with effects
associated to the volcanic activity. A special case is the crater
itself, which is detected as a thermal anomaly, but it goes almost
unnoticed as a spectral anomaly in the reflective range.
Hydrothermal alteration detected from HyMAP in Turrialba and
environment, is linked to crops and bare areas, as well as to
artificial surfaces (roofs of buildings mainly). This does not
mean that in the vicinity of these areas there are not
hydrothermal alteration minerals. It can be observed that the
detection is strongly influenced by the contribution of the
broad, dense and homogeneous natural vegetation cover
existing on the spectral information recorded by space sensors.
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
5. CONCLUSIONS
It has been carried out a comparative study of the spectral
anomalies and the hydrothermal alteration materials detected
from HyMAP and MASTER data, on the Turrialba volcano and
its environment.
It has been found that a higher spectral resolution of the images
improves accuracy in the detection of diagnostic bands of the
hydrothermal alteration minerals analyzed. A higher
dimensionality of the data implies however a greater number of
samples to typify classes of materials.
Higher concentrations of hydrothermal alteration minerals, in
scenarios where the sources of error (mainly vegetation) are
minimized, are correlated with the anomalies calculated in the
spectral range reflective. It has not been established a clear
relationship between thermal anomalies and minerals analyzed.
The spectral mixing, associated directly with the spatial
resolution, the airborne sensors and the satellites used, has an
impact, in a significantly way, on the characterization of the
background, and thus in the calculated spectral anomalies.
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