-B3, 2012
0 (maximum
ibility) based on
VI results were
oil moisture data
tween these two
y Edge
let Edge
ve
NDVI
I adapted from
ll data obtained
0 investigate the
to facilitate this
g the rain gauge
results indicated
11 in most cases
after rain events,
ain several days
For example, at
17, 73 and 225
sed again after
3a) The same
where the TVDI
the rain events,
81, 137 and 241
Bainfali iem)
: 8
300 350
and (b) Suao.
32 Spatio-temporal evolution of surface soil moisture
Figure 4 shows the spatio-temporal evolution of TVDI from
January to December 2009. In general, the TVDI results (values
from 0 to 1) show a large degree of variation in TVDI values over
space and time. Low TVDI values (0 — 0.4) were generally
observed at water surfaces and high elevation mountain areas.
Higher TVDI values (0.4 - 0.6) were observed in the plains and
lower elevation parts of the study area. High TVDI values (0.6 -
0.8 and 0.8 - 1.0) were observed mainly in coastal and residential
areas. The regression analysis between TVDI results and
AMSR-E soil moisture data (Figure 5) was performed to find the
transformation function between the two datasets. This was done
to convert the TVDI to the real soil moisture data that had the
same unit with AMSR-E soil moisture data (i.e. g cm”). The
results indicated that there was good agreement between the two
January 11 February 25
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B3, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
datasets. The mean correlation coefficient was -0.82 and the root
mean squared error (RMSE) to quantify the difference between
the two datasets was 39.8. These results confirmed that the
AMSR-E soil moisture data (25-km resolution) can be used to
transform TVDI results to surface soil moisture data with a
higher spatial resolution (1-km resolution).
Figure 6 showed the spatial distributions of surface soil
moisture (achieved by regression analysis between TVDI and
AMSR-E soil moisture). In general, the spatio-temporal
evolution of TVDI-derived soil moisture was comparable with
those from AMSR-E data throughout the year. The areas of low
soil moistures were generally concentrated in the west part of the
study area, where most residents settled in the cramped plains.
The areas of low soil moistures were expanded from April, but
likely returned to wet conditions by the end of September due to
the monsoonal influence.
March 16 April 28
ga =
November 04
Figure 4. Spatiotemporal evolution of monthly TVDI during 2009.