i Detection of Smoke and Dust Aerosols Using Multi-sensor Satellite ...

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4.2 Methodology
Dust over bright surface
Clear bright surface
Reflectance Response curve of dust and clear bright pixels by statistical analysis
B8 B3 B4 B1 B2 B7 B20 B29 B31 B32
MODIS band
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412 469 555 645 858 2130nm; 3.75 8.55 11.03 12.02μm
Figure 4.3: Response curves of dust and clear bright pixels.
4.2.1 Threshold and accuracy analysis
The scatter plots of NDDI, BTD (12, 11), BTD (3.7, 11), and logarithm of single
reflectance of band 1, are given in Fig. 4.4 to decide the thresholds of each test. Each data
point is the average value of one dust events, along with standard deviation. Figs. 4.4a
and 4.4b show a large difference of NDDI and BTD (12, 11) values between cloud and
dust. Cloud has negative BTD (12, 11) and NDDI values while dust has positive values
of these two indices contrarily. The dust has larger BTD (3.7, 11) values than clear bright
surface (Fig. 4.4c) and clear dark surface (Fig. 4.4e). Among them, the BTD (3.7, 11)
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BT (K)