429
Microwave Vegetation Indices from Satellite Passive Microwave Sensors
(0.36–0.62) and MVIs (A: 0.30–0.49 and B: 0.12–0.23). Land covers with low coefficients of variation include broadleaf forests (both evergreen and deciduous), savannas, and woody savannas with 0.20–0.24 for NDVI, 0.08–0.18 for A, and 0.05–0.10
for B parameters. The other land covers (cropland, grassland, and shrubland) have
moderate coefficients of variation values for both NDVI and the MVIs.
The coefficients of variation of A are only slightly lower than those of NDVI,
and both have very similar distribution patterns above 20°N latitude (Figure 18.4a
through 18.4c). Below 20°N, especially over Africa, there are some disagreements in
the patterns, primarily when the A values are less than 0.10. This can be attributed
to the small standard deviation and large mean values in these regions, which results
in the small coefficients of variation values.
The MVI B values, especially for the high-frequency pair, exhibit a large seasonal variation for evergreen broadleaf forests, with magnitudes comparable to those
of grassland, cropland, and the evergreen needleleaf forest. On the other hand, the
coefficients of variation of NDVI for these regions are comparable to those of barren
or dessert regions. This is clearly shown in Figure 18.4e for the tropical rain forest
regions near the equator. This effect is mainly due to the very low mean values of B
parameters in these regions.
18.4.3 analySeS of Mvi’S new infoRMation foR vegetation MonitoRing
To assess whether the microwave vegetation indices have significant new or complementary information compared to NDVI, we performed the following analyses: (1)
examination of the global distribution pattern of the correlation coefficient between
TABLE 18.2
Global Mean Values of Coefficient of Variation of MVIs and NDVI for
Different Vegetation Types in 2003
Land Cover
a(6.925 GHz/
10.65 GHz)
a(10.65 GHz/
18.7 GHz)
B(6.925 GHz/
10.65 GHz)
a(10.65 GHz/
18.7 GHz)
NDVI
Evergreen
needleleaf forest
0.3972
0.3693
0.1234
0.1490
0.4417
Evergreen
broadleaf forest
0.0981
0.0821
0.0548
0.1037
0.2052
Deciduous
needleleaf forest
0.4238
0.4916
0.1715
0.2265
0.6253
Deciduous
broadleaf forest
0.1850
0.1408
0.0723
0.0783
0.2435
Mixed forest
0.3065
0.3235
0.1192
0.1560
0.3562
Shrubland
0.3273
0.3398
0.0632
0.0869
0.3470
Woody savannas
0.1691
0.1334
0.0895
0.1039
0.1956
Savannas
0.2033
0.1605
0.0778
0.0961
0.2156
Grasslands
0.3249
0.3353
0.0825
0.1274
0.3064
Croplands
0.2701
0.2682
0.0807
0.1057
0.3515
Microwave Vegetation Indices from Satellite Passive Microwave Sensors
(0.36–0.62) and MVIs (A: 0.30–0.49 and B: 0.12–0.23). Land covers with low coefficients of variation include broadleaf forests (both evergreen and deciduous), savannas, and woody savannas with 0.20–0.24 for NDVI, 0.08–0.18 for A, and 0.05–0.10
for B parameters. The other land covers (cropland, grassland, and shrubland) have
moderate coefficients of variation values for both NDVI and the MVIs.
The coefficients of variation of A are only slightly lower than those of NDVI,
and both have very similar distribution patterns above 20°N latitude (Figure 18.4a
through 18.4c). Below 20°N, especially over Africa, there are some disagreements in
the patterns, primarily when the A values are less than 0.10. This can be attributed
to the small standard deviation and large mean values in these regions, which results
in the small coefficients of variation values.
The MVI B values, especially for the high-frequency pair, exhibit a large seasonal variation for evergreen broadleaf forests, with magnitudes comparable to those
of grassland, cropland, and the evergreen needleleaf forest. On the other hand, the
coefficients of variation of NDVI for these regions are comparable to those of barren
or dessert regions. This is clearly shown in Figure 18.4e for the tropical rain forest
regions near the equator. This effect is mainly due to the very low mean values of B
parameters in these regions.
18.4.3 analySeS of Mvi’S new infoRMation foR vegetation MonitoRing
To assess whether the microwave vegetation indices have significant new or complementary information compared to NDVI, we performed the following analyses: (1)
examination of the global distribution pattern of the correlation coefficient between
TABLE 18.2
Global Mean Values of Coefficient of Variation of MVIs and NDVI for
Different Vegetation Types in 2003
Land Cover
a(6.925 GHz/
10.65 GHz)
a(10.65 GHz/
18.7 GHz)
B(6.925 GHz/
10.65 GHz)
a(10.65 GHz/
18.7 GHz)
NDVI
Evergreen
needleleaf forest
0.3972
0.3693
0.1234
0.1490
0.4417
Evergreen
broadleaf forest
0.0981
0.0821
0.0548
0.1037
0.2052
Deciduous
needleleaf forest
0.4238
0.4916
0.1715
0.2265
0.6253
Deciduous
broadleaf forest
0.1850
0.1408
0.0723
0.0783
0.2435
Mixed forest
0.3065
0.3235
0.1192
0.1560
0.3562
Shrubland
0.3273
0.3398
0.0632
0.0869
0.3470
Woody savannas
0.1691
0.1334
0.0895
0.1039
0.1956
Savannas
0.2033
0.1605
0.0778
0.0961
0.2156
Grasslands
0.3249
0.3353
0.0825
0.1274
0.3064
Croplands
0.2701
0.2682
0.0807
0.1057
0.3515