al
., 1994; Moran
et al
., 2004; Petropolous, 2009). An irrigated
crop is expected to have both low surface temperature and high
vegetation cover as compared to other land uses. Therefore,
the joint use of temperature and
NDVI
is needed for the study of
irrigated crops (Moran
et al
., 1994).
NDVI
at high frequency, and
at medium to fine resolution, is available from satellites such
as RapidEye, QuickBird and WorldView. Surface temperature,
however, is available at medium to coarse resolution. Land-
sat-7 and
ASTER
, used in this study, provide synchronous
NDVI
and surface temperature at moderate resolution.
The approach to detect “irrigated” crops presented in this
study is most suited to arid or semi-arid areas where rainfall
is not a confounding factor. In such environments,
NDVI
alone
may provide some indication of irrigated crops but for in-
season changes in irrigation practices, temperature differences
are needed. The
CGID
is a semi-arid area but did receive some
rainfall during the irrigation season from September 2012 to
May 2013. The amount of seasonal totals were low and uni-
form with 62.7 mm in spring, 64 mm in summer and 64.7 mm
in autumn, although there were some spikes that occurred
T
able
4. E
valuation
of
I
rrigation
C
lassification
(a) Occurrence
Occurrence
according to
Classification
Occurrence according to Water Delivery Records*
Spring
Summer
Autumn
Irrigated Non-irrigated Irrigated Non-irrigated Irrigated Non-irrigated
Spring
Irrigated
2011
501
0
0
0
0
Non-Irrigated
0
16
0
0
0
0
Summer
Irrigated
0
0
1431
158
0
0
Non-Irrigated
0
0
0
939
0
0
Autumn
Irrigated
0
0
0
0
1608
222
Non-Irrigated
0
0
0
0
0
698
* Victorian Water Register (waterregister.vic.gov.au/).
(b) Accuracy
Farms
Producer’s Accuracy % User’s Accuracy %
Spring
Irrigated
100
80
Non-Irrigated
3
100
Summer
Irrigated
100
90
Non-Irrigated
86
100
Autumn
Irrigated
100
88
Non-Irrigated
76
100
Overall Accuracy = 88.4%
Figure 11. Rainfall at a representative weather station (Tatura) located within the study area during 2012/2013.
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
March 2015
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