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Title
Mapping without the sun
Author
Zhang, Jixian

coarse satellite orbit as possible, this paper employs precise
orbits issued by TU Delft University. (f) atm is always not very
easy to model and estimate, which can be removed afterwards
as well as (f> noi by filtering technique. In the end we have got
Qdef
which is what we are interested in most.
3 CASE STUDY
3.1 Data Sets
The basic data for two-pass D-InSAR is SAR pairs and external
DEM. The SAR pairs are used to generate the interferogram
comprising the deformation information. The aim of using
external DEM is used to remove topographic contribution from
the interferogram.
This paper collects 6 ERS SAR SLC images covering Fushun
city, Liaoning province, and their swathes are all about
lOOkmx 100km. The time spans May 1993 to Jun 2000, and the
frames are all 2763. The parameters of the example SAR pairs
are listed in Table 1, the average spectral overlap is more than
85%. The external DEM we adopted is USGS SRTM DEM
issued on the internet (ftp://e0srp01u.ecs.nasa.gov). The DEM
covering our research area available only has 3 arc-seconds’
(90m) sample spacing with 3.7 m standard deviation, seen in
Figure 1-b.
Figure 1-a SAR image acquired on July 14 1998 Figure 1-b. Mosaic SRTM DEM covering Fushun city
No.
Mission
Orbit
No.
Master
Slave
ЛТ
(days)

(m)
Spectral overlap
Range
Azimuth
1
ERS-1
09667
1993/05/22
1995/04/10
688
-27
97. 5
96. 8
2
ERS-1
19530
1995/04/10
1996/06/04
421
-397
63.2
83. 1
3
ERS-2
05869
1996/06/04
1998/07/14
770
14
98. 7
99.3
4
ERS-2
16891
1998/07/14
1999/09/07
420
65
94. 0
100
5
ERS-2
22903
1999/09/07
2000/06/13
280
251
76.8
70.4
Table 1. Basic parameters of interferometric pairs
3.2 Data Processing
To reduce errors from co-registration and flat earth phase
removal, we used the precise ERS orbit data from Delft
University of Technology. Consequently, we need execute
general coarse to fine coregistration between master and slave
images, and between simulated SAR image from SRTM DEM
and master image. To suppress noise, the SAR images are
processed by a multi-look operation of 5 pixels along the
azimuth direction to obtain a final resolution of 20 x 20m, and
filter the interferogram with a new modified Goldstein
algorithm(Ding, 2006) in frequency field, and compared with
the rectangular filtering, our method improved the quality of
differential interferogram about 28%. The starting coherence
threshold is set to the average coherence value 0.12 and the
interferograms are unwrapped with the iterative disk masking
algorithm. The unwrapped interferograms are mapped to slant
range ground surface deformation, and then geocoded and
projected to the vertical direction so as to reflect height change.