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

6.2 Validating Dust Detection with CALIPSO
The CALIPSO is an effective tool for validating the dust detection. It is capable of
separating airborne dust from ground dust with the vertical information of aerosol and
cloud layers. As illustrated in Chapter five, the CALIPSO VFM classifies various scene
features into several types. Therefore, the VFM product is used for the quantitative
validation of dust detection results.
Fig. 6.4 shows a dust storm event over Taklimakan Desert captured by Aqua
MODIS on July 26, 2006. The image is generated with measurements extracted from two
swaths at UTC time 7:25 and 7:30. The dust aerosol is located at the eastern desert. The
blue dash line is the footprint of CALIPSO in this area. The dust image generated from
multi-spectral approach is displayed in Fig. 6.5. The VFM product of the region marked
by blue dash line in Fig. 6.4 is shown in Fig. 6.6. The validation is executed by matching
pixels from two sensors with their geolocation measurements in the overlapping region. It
is worth noting that the misclassification of labeling dust aerosol over desert area as cloud
is observed which is mentioned in Chapter five. The dust aerosol layer marked in the
black circle is misclassified as cloud in Fig. 6.6.
The error analysis is performed to count the number of pixels identified (pixel is
labeled as dust aerosol with both sensors), unidentified (pixel is labeled as dust aerosol
with only CALIPSO but undetected with MODIS), and misidentified (pixel is labeled as
non-dust aerosol pixel with CALIPSO but detected with MODIS). According to spectral
curves of dust aerosol in Figs. 4.2 and 4.3, red band is a key spectral band able to reflect
the intensity of dust aerosol loading. Usually, the stronger the dust storm is the higher
87