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Figure 3 Map of the vertical displacement of the urban areas of Tangshan measured with ERS differential SAR interferometry
between 1997 and 1998. The results were exported to and post-processed in the GIS. The subsidence regions can now be seen clearly
and the color coding indicates the magnitude of subsidence. After overlapped with the Mine Area map, we can see it has largest
displacement in Tangshan Mine area, in Gangyao Mine and Majiagou Mine, it has average 10 cm displacement, in west of Tangshan
Mine, and it has average 15 cm displacement due to the Kast collapse.
From Pos: 39* 37'38.3(To Pos: 39* 35' 49.13" N,118* 18'59.38" E
0.25 m
0.20 m
0.15 m
(a)Position profile #1
Figure 4 Profiles of the vertical displacement velocity obtained from
directions over the subsidence area of Tangshan Mine.
From Pos: 39* 36'26.3To Pos: 39* 36'09.26" N, 118* 12’02.79" E
(b) Position profile #2
SAR interferometry between 1997 and 1998 along two
4.2 Envisat
The interferogram formed with the two Envisat ASAR images
contains both the topography and subsidence, the SRTM-DEM
with 90m resolution was used as the reference DEM. The
coherence and the differential interferogram are presented in
figure 5, the data was filtered and multi-look processed to
improve phase statistics, we can see from the figure that only
the urban areas and Guye district has high coherence.
To date, ten ENVISAT images have been acquired near the
same site during 17 Jan. 2004 and 17 May 2007. Unfortunately,
the baseline distance of some pairs is over 700m, and it failed
to give sufficient spectral overlap between the two images. The
characteristics of the local vegetation cover make it difficult for
C-band images to conserve sufficient coherence over only one
year. In near future, the Permanent Scatterers (PS) technique
will be used to improve the accuracy of InSAR and D-InSAR
in monitoring the surface subsidence.
