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Mapping without the sun
Zhang, Jixian

Y. L. Chen“, X. L. Ding*', C. Huang 1 Z. W. Li , b
a. Department of Land Surveying & Geo-Informatics, The Hong Kong Polytechnic University, Hong Kong
b. Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China
c. Graduate School of the Chinese Academy of Sciences, Beijing 100039,China
ylchen@shao.ac.cn, lsxlding@polyu.edu.hk
KEY WORDS: D-InSAR ; Two-pass; Mining Subsidence
Continuous mining will make the rock mass near the minery lose balance, which will then result in different geological hazards, such
as landslide, rock movement, earthquake, ground fissures, etc. After more than 100 years’ mining, Fushun city, Chinese mine capital,
have seriously suffered from these kinds of damages. It is essential to carry out long-term and real-time monitoring of the progress of
the mining subsidence in Fushun city. Such monitoring will help to prevent the geological hazards on one hand and improve the
planning and designing of mining activities and systems on the other. D-InSAR (Differential Synthetic Aperture Radar Interferometry)
provides a new remote sensing tool to monitor land motion with high precision, wide coverage, and under nearly all weather
condition. This paper uses 6 ERS-1 and ERS-2 SAR images acquired from May 22, 1993 to Jun 13, 2000 and covering Fushun city,
and the 3 arc second SRTM DEM to conduct two-pass differential SAR interferometry. They can form 15 differential interferograms
in total, but only 5 with satisfactory baseline and coherence. By investigating the 5 interferometric pairs, we obtain the subsidence
rate of Fushun city. The case study verifies that D-InSAR technique is able to detect cm-level subsidence of the mining area.
Traditional deformation monitoring system in most mines
includes GPS surveys, conventional precise levelling and
theodolite surveys, Electronic Distance Measurement surveys,
remote electronic monitoring, etc. However these techniques
are costly, time-consuming, high influence of field and weather
conditions, and obviously inefficient compared with remote
sensing technique such as Differential Synthetic Aperture
Radar Interferometry (D-InSAR), which provides a new
advanced tool for monitoring the ground movement over large
areas of the mine and long interval from months to years,
what’s more, whose deformation accuracy has been up to 3mm
level theoretically. These obvious advantages make scientists
investigate the motions of the land surface using D-InSAR
technique. Timmen (1996), Perski (2001), Ge (2001, 2004), and
Jarosz (2003) et al. have ever carried out studies on mining
subsidence monitoring with D-InSAR technique and have got a
lot of encouraging achievements, while related application have
been seldom carried on in China .
In general, there are three main D-InSAR techniques: two-pass;
three pass; and four pass. This paper employs 2 -pass D-InSAR
technique with 5 pairs of ERS SAR images and SRTM DEM to
monitor 7 years’ average subsidence rate. The result shows that
D-InSAR technique is able to detect cm-level subsidence of the
mining area.
Mathematically, the phase measurements of the repeat-pass
InSAR, ^ and ^ , can be written as y/ = + n ,
^2=y^2+«2 (1)
Where R ] and R 2 are the slant ranges between a ground
resolution cell and the SAR platform; A is the radar
wavelength; Yl x , Tl 2 are noises generated by different
scattering features and other noises. Then the interferometric
phase theoretically is:
0 = i//\-y /l =—(R x -R 2 ) + (n l -n 2 ) (2)
Meanwhile, (f) can be physically divided into two parts as
follows, which is corresponding to the two components in
function (2) respectively:
= (fiflat + topo +( />def)
t . . . . (3)
+ (0ork +( Patm +0noi)
where (f)ji at , due to earth curvature, topographic phase, orbit
error,atmospheric delay, and noise respectively.
The destination of D-InSAR is to extract (f> de j , so we need
remove the reluctant phase. (J) f]al can be removed by using
the known baseline and earth model geometry functions;
0topo can be subtracted by InSAR pairs of short interval or
external DEM , which is the most essential difference between
two pass , three pass, and four pass D-InSAR. Two-pass
D-InSAR adopts the external DEM to obtain (f> topo , but
three-pass and four- pass use the DEM from interferometric
SAR image pairs. To reduce the phase error (f) orb due to the