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Mapping without the sun
Zhang, Jixian

M. He 3 ’, X. F. He 3 *
a Institute of Satellite Navigation & Spatial Information System,
Hohai University, Nanjing, Jiangsu, China 210098
hezhuminlei@hhu.edu.cn xfhe@hhu.edu.cn
KEY WORDS: InSAR, coherence, urban earthquake, damage level detection
Synthetic Aperture Radar (SAR) is one of the most potential sensors for remote sensing technologies since it is not affected by
On December 26, 2003 an earthquake devastated the city of is to demonstrate the feasibility of using interferometric
Bam. Bam is located in the margin of Kavir-e-Lut desert in the coherence magnitudes derived from Envisat-ASAR data to
south-eastern part of Iran. The city of Bam had a population of assess the damage caused by the Bam earthquake,
around 90,000 prior to the earthquake. The estimated
population in the earthquake affected area was around 200,000.
The earthquake had a magnitude of Mw=6.5 (USGS). Around 2. ESTIMATION OF COHERENCE AND COHERENCE
50,000 people were killed, over 30,000 people were injured and CHANGE INDEX
about 75,000 people became homeless by this event. The
earthquake destroyed almost 70 percent of the conjugated cities 2.1 Estimation of the coherence coefficient
of Bam and Baravat and the historical of Arg-e-Bam (2,000 -
2,500 years old mud-brick citadel - the largest mud-brick The complex coherence image between two images ( S{ and s 2 )
construction in the world prior to the earthquake. After IS defined as:
earthquake, International Centre for Geohazards (ICG) had
drawn damage mapping of the Bam city based on IKONOS
imagery and field survey data [1]. , rr „ * 11
routine tool for measuring coseismic displacements [2-4]. Using
dislocation models the data have been exploited to estimate
different parameters of the fault rupture and to compute stress The coherence coefficient is defined by | y \ and its estimator
changes in the crust. Thus, InSAR phase observations have
provided new insights into the mechanical properties of active
fault systems.
clouds and lights. The InSAR analysis, using phase information of backscattering echoes from objects on the earth’s surface, is
successfully employed to quantify relative ground displacements resulting from natural disasters. In this paper, a coherence change
index is presented based on the coherence coefficient of the SAR interferometric analysis which is a sensitive parameter for the
detection of superficial change and the classification of land use. And the feasibility of earthquake-induced urban damage detection
is investigated using the coherence change index. The method proposed is tested by SAR images of the Bam earthquake in 2003.
The results show that there are close relationships between building damage level and the coherence change index. Thus, urban
damage levels are mapped based on the index. The map is consistent with the results from the International Centre for Geohazards.
assessment has the significant advantage of being independent
of cloud cover or time of day. The main objective of this paper
Interferometric synthetic aperture radar (InSAR) has become a
Another interferometric product, the magnitude of the
interferometric coherence, is often used as a measure of quality
of the phase measurement, but rarely interpreted beyond that.
However, the coherence magnitude is a sensitive measure for
temporal changes on the imaged surface and has been suggested
to be useful for mapping seismic damages [5]. Earthquake
damage mapping, if conducted immediately following the event,
can provide vital information to guide disaster response and
emergency relief operations. Such damages have been assessed
using optical space-borne imagery [6]. It has been noted though,
that high resolution optical images are necessary to achieve
reliable results. Using the interferometric coherence for damage
|£Z 5 i w ) 5 2(».rn)e~ M "' m) I
2.2 Estimation of coherence change index
The coherence coefficient change was analyzed in the
interferogram spanning the earthquake with respect to the
interferogram before the event. A coherence change index k is
* X. F. He is the corresponding author.