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

3.2.3 Training data collection
Surface geology and wood species, two key parameters affecting the spectral
response of smoke received by sensor, vary with site by site. The geology decides the
reflectivity of the surface and the wood species determines the component of smoke
plume. The amount of training data in given area determines the applicability of the
algorithm. In this manner, eighteen smoke plumes with various intensities occurred in
USA during last five years (2000-2005) are selected as training data to perform the
statistical analysis. Around 200,000 smoke pixels are collected with visual identification,
and separated into two classes using MODIS land/sea mask product: smoke pixels over
land and ocean respectively. Moreover, bright land pixels, dark land pixels, and cloud
pixels are also colleted for deciding the bands and thresholds of each index.
3.2.4 Spectral curves
The spectral responses of several major scene types are calculated statistically from
training data, given in Figs. 3.4 and 3.5. The spectral responses at ten bands are plotted in
these two figures since those bands are usually used for aerosol detection. The spectral
response at each band is the mean value of all training data for each scene type with the
standard deviation. Since part of smoke events occurred in eastern or western USA may
spread over the oceans, the spectral curves of smoke are separated into two classes:
smoke over land and smoke over ocean. For easily comparison, spectral curves of smoke
(both over land and ocean) and cloud are plotted in Fig. 3.4. The curves of smoke (over
land only) and land (both dark and bright surfaces) are plotted in Fig. 3.5. The abscissa of
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