Results and Discussion
Rice plant growth observation from the field work is shown on figure 3.1 by using time series geo-tag photographs. It shows changes of the color of plants from light green, green to yellow during the rice cycle.
Figure 3.2 illustrates rice plant height time series in each field site. According to the time series graph, rice plant grows more than 1.2 m height and plants are growing in uniform speed.
Plant height and VI
We can observe how VI changes with plant height from the graphs of figure 3.3. When plant height reach between 0.7 m and 1.0 m, NDVI and EVI show their peak values during the plant cycle. However both NDVI and EVI have similar pattern with plant height. At the start of the season VI, proportionally the plant height increases and come to peak level then it decreases while plant height increase.
Rice Acreage and SOS mapping
The paddy cultivation seasons with cultivation area mapping was mapped using both NDVI and EVI time series by threshold method. Figure 3.4 shows maps of rice crop season from NDVI and EVI respectively in Sakeo Province. Total rice cultivation area in Sakeo province is calculated from both analyses. They are 138795.16 ha and 152944.08 ha from NDVI and EVI respectively.
Rice crop cultivation starting month for a single crop area (mapped?) by NDVI and EVI are shown in figure 3.5. Both analyses showed more than 80% paddy fields in single cropping area cultivation were started in June, July and August.
Double rice cropping area has two cultivations which has a starting month for each paddy area. April and May are the starting months for 1st cultivation season and July, August are the starting months for 2nd cultivation season in double crop area. Figure 3.6 and 3.7 shows the starting months for 1st and 2nd cultivation seasons with time series analysis using both NDVI and EVI time series.
Overall accuracy of NDVI based rice paddy area mapping is 77.43% and Kappa statistics is 0.55.
EVI based rice acreage mapping overall accuracy is 76.47% and Kappa statistics is 0.52. Confusion matrices from both analyses are shown in table 3.1 and 3.2.
Table 3.1 – Accuracy assessment result of NDVI based rice acreage mapping
NDVI Non Paddy Paddy Total Producer’s Accuracy (%)
Non Paddy 89 19 108 82.41
Paddy 32 86 118 72.88
Total 121 105 226
Consumer’s Accuracy (%) 73.55 81.90
Overall Accuracy (%) 77.43
Table 3.2 – Accuracy assessment result of EVI based rice acreage mapping
EVI Non Paddy Paddy Total Producer’s Accuracy (%)
Non Paddy 100 34 134 74.63
Paddy 18 69 87 79.31
Total 118 103 221
Consumer’s Accuracy (%) 84.75 66.99
Overall Accuracy (%) 76.47
Rice paddy area based statistics were used to calculate province-level and district-level rice acreage accuracy. According to the rice statistics in 2012/13, total rice cultivation in Sakeo province by NDVI is 138795.16 ha and by EVI 152944.08 ha and 135265.6...