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

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MODIS L1B<br />

measurements<br />

<strong>Dust</strong> aerosol over bright surface<br />

Ln(R1)≤-1.2<br />

& BT20-BT31≥25K<br />

<strong>Dust</strong> storm<br />

pixels<br />

Figure 4.5: The flowchart <strong>of</strong> the dust storm detection<br />

Table 4.4: The tests <strong>and</strong> thresholds used for detecting dust storm; <strong>and</strong> sensitivity analysis<br />

based on the selected dust storm events in China during years 2001-2007.<br />

Bright surface Dark surface<br />

Class Type Threshold test<br />

Value Error (%) Value Error (%)<br />

<strong>Dust</strong> over l<strong>and</strong><br />

Cloud<br />

Total<br />

Y<br />

N<br />

N<br />

BT 3.7 –BT 11<br />

& Ln (R1)<br />

(B7-B3) / (B3+B7)<br />

& BT 12 –BT 11<br />

(R7-R3) / (R3+R7) ≥ 0.0<br />

& BT32-BT31 ≥ 0.0<br />

Y<br />

<strong>Dust</strong> & surface scenes<br />

L<strong>and</strong> pixels<br />

<strong>Dust</strong> &<br />

Noise<br />

Discrete<br />

pixel?<br />

56<br />

25 K<br />

-1.2<br />

0.0<br />

0 K<br />

<strong>Dust</strong> aerosol over dark surface<br />

2.843<br />

2.294<br />

1.886<br />

0.334<br />

1 5.976<br />

20 K<br />

-1.6<br />

0.0<br />

0 K<br />

2.623<br />

4.416<br />

12.484<br />

0.845<br />

1 17.717<br />

1 The total errors <strong>of</strong> both over bright <strong>and</strong> dark surface are not equal to the summation <strong>of</strong> errors from<br />

each test because the overlap exists among tests.<br />

N<br />

Y<br />

Y<br />

N<br />

Cloud pixels<br />

Pre-store<br />

surface types<br />

Ln(R1)≤-1.6<br />

& BT20-BT31≥20K<br />

Noise pixels

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