The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Voi. XXXVII. Part B7. Beijing 2008
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Figure 4-4 Local fire points on August 11 th
Figure 4-5 is scatter plot of brightness temperature of band 22
and band 23, the abscissa is band 22; Figure 4-6 is scatter plot
of the brightness temperature of band 20 and band 21, and the
abscissa is band 20. We can clearly see abnormal points from
the plot. Abnormal points are far away from points group.
These abnormal points are most likely due to the saturation of
bands 20, 22. The uncertainty data is in band 22 which can be
got from HDF document. Many researchers use band 21 only
because of its unsaturation, and abnormal data in band 20 and
band 22 was often discarded. Our experiment shows that it is an
efficient way to use these "abnormal" data combining with band
7 to detect high temperature fires.
Figure 4-5 Scatter plot of bands 22, 23
Figure 4-6 Scatter plot of bands 20, 21
4.2.2 Non-high Temperature Fires Judged with
Comprehensive Threshold Criterion
Non-high temperature fires include three major types: i) before
the fire occurred with the temperature lower than ignition
temperature; ii) after fire occurred, the temperature had fallen,
but higher than normal temperature; iii) The fire point is at high
temperature, but the firing area is smaller than that of a pixel.
There are many difficulties and uncertainties in non-high
temperature fire monitoring, particularly the third category of
non-high temperature fires. Therefore, many researchers define
the fire point that burning area is larger or equal to one pixel
size. With non-high temperature fires complex situations
considered, a comprehensive threshold criterion is used in our
work. We combine visible, near-infrared, mid-infrared and
thermal infrared bands together to get an integrated application.
First, visible and near infrared bands (MODIS bands 1, 2) are
used to generate NDVI. NDVI has two roles: i) The fire area
where NDVI is less than 0.3 generally reveals combustibles; ii)
Generally, there are unbumed vegetations with higher NDVI
around the fire place. The above two are used together to judge
forest fire points. At the same time, according to the
characteristics of the forest fire, we use the differences of
brightness temperatures between band 21 and band 31 to judge
fires. The comprehensive threshold is:
NDVI < 0.3
BT 2X -BT M > 15 ( 4_1 )
' BT 2X >315
BT 2X > aver(BT 3X )
Where BT 2 i is the brightness temperature of band 21, BT 3 i is
the brightness temperature of band 31, aver (BT 3t ) is the
average non-cloudy pixel’s brightness temperatures of band 31.
Suspected fire points are generated with the comprehensive
threshold, a second judgment is followed which purpose is to
identify whether the background pixels are forest. It can be
achieved with NDVI. Figure 4-7 is the result of using
comprehensive threshold on August 11 th , 2006.
Figure 4-7 The suspected fires points generated by threshold
criterion on NDVI of August 11 th , 2006 (red areas were
suspected fires, high temperature points in low NDVI were
suspected as urban heat islands)
In Figure 4-7, the further judgment is based on background
pixels. If we can integrate land-use data, the accuracy will be
improved. We can exclude most places with high temperature
result from urban heat island. Other high temperature points
may be fire points or ground facilities (further judgments with
ground truth are needed).
In order to make a further test, we extracted and analysed the
data on August 8 th and August 30 th , 2006. Figure 4-8, figure 4-9,
figure 4-10 and figure 4-11 were the results.
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