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

6.1.4 Validation of dust monitoring with OMI UVAI
The dust storm in center China was captured by Aqua MODIS on October 23, 2007
at UTC time 04:55. The MODIS true color image is shown in Fig. 6.3a and
corresponding dust image generated with algorithm illustrated in Chapter 4 is shown in
Fig. 6.3b. The UVAI values associated with dust aerosol are usually larger than 1.2
according to the procedure of aerosol selection in OMAERUN README file. Therefore,
only the areas with UVAI values larger than 1.2 in OMI UVAI image are shown in the
Fig. 6.3c. With comparison, totally about 187,472 pixels are labeled as dust with OMI
UVAI product. Among these pixels, 137,554 pixels are labeled as the dust either in
MODIS dust image, but 49,918 pixels are undetected. About 3.67% (6,871 pixels) are
identified as dust in MODIS dust image but labeled as non-dust pixel in OMI UVAI
image. Fig. 6.3d gives the spatial distribution of all identified, unidentified, and
misidentified pixels. The center part of the dust storm is detected by both images. The
major difference is appeared at the front of dust storm (southeast part) where many pixels
are labeled as dust aerosol in OMI UVAI image. Statistically, at the margin area, more
than 5% difference can be attributed to the spatial resolution differences between two
sensors. Moreover, the small clouds floated above the dust storm contribute another
around 3% errors, which is too small to be detected by OMI sensor.
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