Figure 4 shows the extent of ‘Quickbird’ satellite coverage of Bam, acquired
by the University of California at Irvine (UCI), and the Earthquake Engineering
Research Institute (EERI) as part of their Learning from Earthquakes Program.
The first image is dated September 30th 2003 – approximately 3 months before
the earthquake struck. Visual comparison with the second image, taken just
over one week after the earthquake on 3rd January 2004, reveals widespread
changes. Many of the differences are caused by building collapse, although
seasonal variations in vegetation may also be present.
Figure 4 Pan-sharpened QuickBird
satellite coverage of Bam, acquired: (a) in September 2003 ‘before’
the earthquake; and (b) in January 2004 ‘after’ the earthquake. In addition
to differences between the scenes due to urban damage, the greenness
of vegetation has changed because of seasonal effects and sensor look
angle variation. Imagery courtesy of DigitalGlobe, http://www.digitalglobe.com.
These changes were quantified using a texture-based change detection algorithm
originally developed for the 2003 Algerian earthquake. In the resulting building
damage map (Figure 5), red and orange areas are associated with extreme changes
where structures have collapsed. These zones are concentrated within eastern
districts of Bam, a distribution which corresponds closely with preliminary
results of a ground-based damage assessment (National Cartographic Center
of Iran, 2004).
Figure 5 Preliminary VIEWS
damage assessment for Bam, obtained using texture-based change detection.
Red and orange areas correspond with pronounced changes between the
‘before’ and ‘after’ scenes, which are primarily associated with collapsed
buildings. To aid visualization, results are overlaid with QuickBird
coverage from 30th September 2003. Imagery courtesy of DigitalGlobe,