Table 4-1. Derived groups of EVI grouping based on similarity pattern
No Group
EVI Classes No
Group EVI Classes
1 A
Class 1, 4 11
K Class 21
2 B
Class 2 12
L Class 24
3 C
Class 3 13
M Class 25, 26, 27
4 D
Class 5 14
N Class 28, 29, 35
5 E
Class 6 15
O Class 30, 31, 32, 34
6 F
Class 7, 8, 9 16
P Class 33
7 G
Class 10, 11, 12 17
Q Class 36, 39, 42
8 H
Class 13, 14, 15 18
R Class 37, 38, 40, 41, 44
9 I
Class 16, 18, 22, 23 19
S Class 43, 45
10 J
Class 17, 19, 20
Figure 4-4. 19 class of EVI supervised grouping
4.3 Rice Detection
To identify pixel value that represent rice field, multiple linear regression was conducted by comparing the number of pixel in each classification with rice
crop area derived from BPS data. Multiple linear regressions on the data based on 19 classes EVI grouping and crop statistic from BPS give result R
2
of 0,89 which described that the result shows good correlation between crop area and EVI Group
D, Group F, Group G, Group H, and Group J see table 4-2. The 5 out of 19 class resulted from the regression process then were considered as rice field for next
calculation to estimate the rice production in Karawang, Subang, and Indramayu Regency.
Table 4-2. Multiple linear regressions result
Regression Statistics Multiple R
0.945829 R Square
0.894593 Adjusted R
Square 0.868266
Standard Error
2202.428 Observations
59 ANOVA
df SS
MS F
Significance F Regression
5 2.22E+09
4.45E+08 91.65966
7.69E-25 Residual
54 2.62E+08
4850690 Total
59 2.49E+09
Coefficients Standard
Error t Stat
P-value Lower 95
Upper 95 Lower
95.0 Upper
95.0 Intercept
NA NA
NA NA
NA NA
NA Group G
1.034164 0.179695
5.755102 4.2E-07
0.673897 1.394431
0.673897 1.394431
Group D 2.233164
0.334074 6.684648
1.34E-08 1.563387
2.902941 1.563387
2.902941 Group H
1.160912 0.194857
5.95777 1.99E-07
0.770248 1.551576
0.770248 1.551576
Group F 1.013324
0.151267 6.698927
1.27E-08 0.710053
1.316596 0.710053
1.316596 Group J
0.544629 0.150224
3.625456 0.000639
0.243449 0.845809
0.243449 0.845809
Based on the regression result, the spatial distribution and the estimated area of rice field in the research area can be identified by using formula:
Rice Area Y = Area Group D + Group F + Group G + Group H + Group J By summarizing the EVI Group EVI Group D, Group F, Group G, Group
H, and Group J, the estimation of rice field can be measured and compared with the existing data from BPS for validation see table 4-3 and figure 4-5. A bias
between estimated area and BPS data can occurred in this process because MODIS EVI data has the spatial resolution of 250m by 250m pixel size,
meanwhile the real condition of rice field can be smaller or bigger than 250m by 250m.
Table 4-3. Rice field area estimation
GROUP Area Ha
D 19.603,9805
F 73.686,4218
G 86.752,9034
H 65.791,9433
J 38.516,5273
Total Rice Field Area 284.351,7763
The harvested areas from BPS data then were compared with the area estimation result from image data. The data from BPS seems to be larger from the
estimation from image data because BPS data measured the harvested area which means that when the rice plantations were harvested twice a year then the area
also multiplied by two most of rice variety planted in the research area were harvested twice a year. To compare the area from BPS data with the result from
image data, the estimation area need to be multiplied by 2 times of harvesting which gives the result of 568.703,5526 Ha of estimated harvested area. The error
was under estimated compared to BPS data with the difference of 7,38 for rice field area.
