Generally, in all four regions throughout the study period,
elevation values were lower than the year 2000
SRTM
values
with some exceptions in the
NW
region. Over the study period
in the Dry Central region, there was a negative elevation differ-
ence trend of −0.04 ±0.14 m a
-1
. This trend indicates a reces-
sion of glacial mass compared to the year 2000, but the uncer-
tainty in this estimation is higher than the elevation difference
trend. In the
DC
region, the maximum mean elevation differ-
ence (Table 2) (Figure 4) was −0.98 ±0.29m in 2005, and mini-
mum elevation difference was −0.13 ±0.18m (Table 2) in 2006.
The overall mass balance in the
DC
region was -0.037 ±0.13m
w.e.a
-1
on the clean ice region. Clearly, there were significant
negative mass balance in
DC
in some years, but in other years,
there were higher uncertainty in the estimated values.
In the North Wet region, elevation differences on clean ice
fluctuated significantly over the study period. However, the
overall elevation difference trend was −0.14 ±0.13m a
-1
. The
mean elevation values were lower than the year 2000 values
in the years 2005, 2006, and 2008, while in 2007 and 2004,
the mean elevation values were little higher than the 2000
value. The maximum mean elevation difference in this region
was −0.64 ±0.5m (Table 2) in 2005, and there was a positive
elevation difference of 0.5 ±0.9m (Table 2) in 2004. Over the
study period, mass balance rate was −0.122 ±0.12m w.e.a
-1
on
the clean ice region.
In the
SPI
there also was a negative elevation difference
trend of −0.04 ±0.05m a
-1
during the study period. In all the
years, the mean elevation difference was lower than the val-
ues in 2000. The maximum mean elevation difference (Figure
4) we observed for this region was −1.17 ±0.09m (Table 2) in
2006 and the minimum elevation difference we noticed was
−0.75 ±0.10m (Table 2) in 2004. Likewise, there was a nega-
tive trend in mass balance (−0.037 ±0.05m w.e.a
-1
).
In the Cordillera Darwin Icefields, there was a negative gla-
cier elevation difference throughout the study period. The over-
all trend in the elevation difference was −0.14 ±0.06 m a
-1
. The
maximum mean elevation difference (Figure 4) we observed in
this region was −1.31 ±0.3m (Table 2) in 2005, and the minimum
elevation difference we noticed −0.11 ±0.6 m (Table 2) in 2004.
The mass balance trend was −0.126 ±0.05m w.e.a
-1
. Among all
the regions,
CDI
showed highest negative mass balance trend.
Conclusions
The objective of this study was to estimate the trends in
glacial mass balance using
GLAS
-
ICESaT
and
SRTM
elevation
models in the Andes of Chile and Argentina. We classified
the study area into
DC
,
NW
,
SPI
, and the
CDI
regions. One of
the challenges of using
ICESaT
data in non-polar regions is
the scarcity of footprints outside the Polar Regions. This is
Figure 5. Average elevation differences per annum and linear trends between ICESat and SRTM data from 2004 through 2008 on clean
ice in four regions.
T
able
2. A
verage
E
levation
D
ifferences
and
T
rends
between
ICES
at
and
SRTM D
ata
from
2004
through
2008
Regions
Average elevation difference per annum (ma
-1
)
Elevation Difference
Trends (ma
-1
)
Mass Balance
Trends (m w.e.a
-1
)
2004
2005
2006
2007
2008
NW 0.53
±
0.9
-0.64
±
0.5
-0.50
±
0.4
0.29
±
0.4
-0.42
±
0.3
-0.14±0.13
-0.122±0.1
2
DC
-0.46
±
0.3
-0.98
±
0.3
-0.13
±
0.2
-0.46
±
0.2
-0.87
±
0.2
-0.04±0.14
-0.037
±0.13
SPI
-0.75
±
0.1
-1.01
±
0.1
-1.17
±
0.1
-0.92
±
0.1
-0.79
±
0.2
-0.04±0.05
-0.037
±0.05
CDI
-0.11
±
0.6
-1.31
±
0.3
-1.19
±
0.3
-0.99
±
0.5
-1.26
±
0.2
-0.14±0.06
-0.126±0.05
816
October 2016
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
