1. NDWI!0
If “NDWI!0” is true, it is a water body. Otherwise, it is other types of land
covers, such as PML, saline land, vegetation cover, bare land, and fallow land.
2. NDVI>0.11
If “NDVI>0.11” is true, it is the vegetation cover; otherwise, it is PML, saline
land, bare land, or fallow land.
3. (b5-b3)/(b5 + b3) !0.28
If “(b5-b3)/(b5 + b3) !0.28” is false, it is either PML or saline land; otherwise, it
is either bare land or fallow land.
4. NDVI 8 >0.3
Bare land and fallow land have similar spectral signatures in May but can be
differentiated by the Landsat images in July/August (peak of the growing season)
since fallow land grows a lot of weeds but bare land doesn’t. Using the NDVI value
at the peak of a growing season can easily distinguish the two. In this study, we use
NDVI8 to represent the NDVI in the peak of a growing season (i.e., July/August). If
“NDVI 8 >0.3” is true, it is fallow land; otherwise, it is bare land, including Bare
Land1 and Bare Land2.
5. b5 > 0.69
If “b5 > 0.69” is false, it is PML, including PML1 and PML2; otherwise, it is
saline land. In above, b5 stands for the reflectance of Landsat TM band 5.
17.2.2 A Specific Example
17.2.2.1 Data Sets and Preprocessing
A region bounded with spatial coordinates of (45
11
0 12
00 N, 84
44
0 24
00 E),
(44
50
0 12
00 N, 86
54
0 24
00 E), (44
29
0 8
00 N, 84
30
0 5
00 E), and (44
8
0 24
00 N, 86
37
0 44
00 E)
contains a large percentage of PML in northern Xinjiang, China, was selected as the
study area. According to the phenological calendar of major crops, including cotton,
winter wheat, and spring corn, in the study area, cotton is planted around middle and
late April and emerges in early May, while corn is planted in late April and early
May. Both cotton and cornfields are mulched with transparent PML. During the
planting and emerging period, the NDVI values of both cotton and cornfields are
very low, while the NDVI values of the winter wheat and other vegetated fields are
high due to the difference in the phonological stages (i.e., winter wheat is at the
jointing and heading stage). Such a phenological difference makes PML easy to be
extracted from satellite remote sensing imagery. In addition, we concern only with
extracting the PML, not with further distinguishing between PML on cotton and
360
L. Lu
If “NDWI!0” is true, it is a water body. Otherwise, it is other types of land
covers, such as PML, saline land, vegetation cover, bare land, and fallow land.
2. NDVI>0.11
If “NDVI>0.11” is true, it is the vegetation cover; otherwise, it is PML, saline
land, bare land, or fallow land.
3. (b5-b3)/(b5 + b3) !0.28
If “(b5-b3)/(b5 + b3) !0.28” is false, it is either PML or saline land; otherwise, it
is either bare land or fallow land.
4. NDVI 8 >0.3
Bare land and fallow land have similar spectral signatures in May but can be
differentiated by the Landsat images in July/August (peak of the growing season)
since fallow land grows a lot of weeds but bare land doesn’t. Using the NDVI value
at the peak of a growing season can easily distinguish the two. In this study, we use
NDVI8 to represent the NDVI in the peak of a growing season (i.e., July/August). If
“NDVI 8 >0.3” is true, it is fallow land; otherwise, it is bare land, including Bare
Land1 and Bare Land2.
5. b5 > 0.69
If “b5 > 0.69” is false, it is PML, including PML1 and PML2; otherwise, it is
saline land. In above, b5 stands for the reflectance of Landsat TM band 5.
17.2.2 A Specific Example
17.2.2.1 Data Sets and Preprocessing
A region bounded with spatial coordinates of (45
11
0 12
00 N, 84
44
0 24
00 E),
(44
50
0 12
00 N, 86
54
0 24
00 E), (44
29
0 8
00 N, 84
30
0 5
00 E), and (44
8
0 24
00 N, 86
37
0 44
00 E)
contains a large percentage of PML in northern Xinjiang, China, was selected as the
study area. According to the phenological calendar of major crops, including cotton,
winter wheat, and spring corn, in the study area, cotton is planted around middle and
late April and emerges in early May, while corn is planted in late April and early
May. Both cotton and cornfields are mulched with transparent PML. During the
planting and emerging period, the NDVI values of both cotton and cornfields are
very low, while the NDVI values of the winter wheat and other vegetated fields are
high due to the difference in the phonological stages (i.e., winter wheat is at the
jointing and heading stage). Such a phenological difference makes PML easy to be
extracted from satellite remote sensing imagery. In addition, we concern only with
extracting the PML, not with further distinguishing between PML on cotton and
360
L. Lu