Role of
Photogrammetry and Remote Sensing in Wenchuan Earthquake Deren Li
It has been demonstrated that photogrammetry and remote sensing has played a crucial role in the aftermath of the earthquake in Wenchuan, Sichuan
An earthquake, measured 8.0 on the
Richter scale, struck Wenchuan
County, Sichuan Province at 14:28 on
May 12, 2008. The epicenter was at
Yingxiu, a town in Wenchuan, as shown
in Figure 1. As indicated in Figure 1, the
middle segment of the Longmen Mountain
earthquake zone encloses the epicenter,
Yingxiu, with the Longmen Mountain zone
being part of the north-south earthquake
zone in China. According to records, there
have been 9 earthquakes larger than a
grade of 8 occurring in the north-south
earthquake zone from 1739, and 7 of
them were after 1897, when the greatest
one was at Haiyun in 1920 and at Chayu
in 1950, both of them measured 8.5.
Figure 1. The Wenchuan earthquake in context
In Wenchuan earthquake, the worst hit
areas include Beichuan and Qingchuan,
with the earthquake intensity measured
at 11, with the maximum being 12 by the
Chinese seismic survey standards. By
12:00 pm on June 14, 2008, the death
toll read 69,170,
with 374,159 people injured, 17,428 people missing,and a population of 48,270,000 severely
affected by this huge disaster. Figure 2
shows the beauty of Beichuan before
the earthquake against the destruction
and devastation after the earthquake.
Figure 2. Pictures showing Beichuan before and after the earthquake.
Under the leadership and organization
of the Chinese government and Premier
Wen Jiabao, and with the support of many
countries and people around the world,
the Chinese people braved against the
devastating earthquake, and carried out
timely and active disaster relief work.
Photogrammetry and remote sensing, as
high-tech, has played an important role
in the fight against this natural disaster.
In Phase I, rescue of people buried under
the rubbles was the main goal. Highresolution
aerial and satellite imagery
were used to locate buildings collapsed in
the worst hit areas so that rescuers were
dispatched. In Phase II, prevention of and preparedness for secondary disasters, i.e.,
landslides and mudslides, especially, those
in and around the quake lakes or barrier
lakes that are formed when a landslide
plugs a river, top the agenda. Air-borne
and space-borne optical imagery and radar
data are required for identifying, assessing,
and decision-making regarding locations
prone to such secondary disasters. Phase
III is concerned with disaster assessment
and reconstruction. It is then necessary
to undertake topographic mapping at
1:10,000 scale in the region with an
areal extent of 120,000 km2 based on
the technique of aerial photogrammetric
survey without ground control points,
generating information products, such as DEMs, DOQs, and DLGs. Topographic
mapping in urban areas is performed at a
larger scale of 1:2,000.
These will better serve
the people in the disaster
areas so that they can
outline reconstruction
of their homes.
Figure 3. Aerial photography flown with
ADS40 (GSD: 0.3 m) showing what was
left of Yingxiu Town in Wenchuan after
the earthquake on May 15, 2008.
Figure 4. The image acquired by Cosmo (at a resolution of 1
m) indicating the locations (white segments) where buildings
are likely collapsed after the earthquake; up to 14.8% of the
areas were suspected to be results of collapsed buildings.
In the struggle against
the destructive quake
in Sichuan, Chinese
photogrammetry
and remote sensing
professionals have, with
supports from colleagues
around the world, made
various contributions
as follows. For Phase I, rapid surveys and assessment of the
disasters are important, as shown by
Figures 3 and 4, with the former being
aerial photography flown with ADS40
(GSD: 0.3 m) showing what was left of
Yingxiu Town in Wenchuan after the
earthquake on May 15, 2008, the latter
being an image acquired by Cosmo (at a
resolution of 1 m) indicating the locations
(white segments) where buildings are
likely collapsed after the earthquake; up
to 14.8% of the areas were suspected
to be results of collapsed buildings.
Figure 5. The change of river water ways due to the forming of quake lakes in Tangjiashan,
as indicated by white regions generated by comparing SPOT5 (10 m resolution) images
taken before (November 10, 2006) and after (May 16, 2008) the earthquake.
Figure 6. The DEM of the quake lake in Tangjiashan, Mianyang city, Sichuan Province,
one of the area worst affected by Wenchuan earthquake, which was generated based
on ALS50 II air-borne LiDAR data with a sampling interval of 2 m, flight date, May
31, 2008, by the State Bureau of Surveying and Mapping, Wuhan University, and
Wuda Geo Information Company (the barrier dam is shown with a inset picture)
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