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squares solution with a minimum norm deformation velocity 
vector constraint (Berardino et al., 2004; Pepe et al., 2005; 
Mallorqui et al., 2005; Blanco et al., 2006) 
3. APPLICATION OF INSAR TECHNOLOGY IN 
CHINA 
InSAR technique has penetrated through almost every surface- 
deformation related monitoring, thanks to the Advanced D- 
InSAR technique. In general, InSAR has evolved to be able to 
monitor and track deformation, with great elegance, of different 
causes including tectonic seismic and volcanic activity, ice and 
rock glacier motion, slope instability, and subsidence caused by 
ground water pumping, mining, hydrocarbon extraction, and 
natural compaction in high precision and reliability. 
In the late 1990s, InSAR technology was introduced into China 
and gained firstly an experimental use and then became 
operational mainly on the subsidence taking place in urban area 
due to either water pumping and/or underground construction, 
besides the active tectonic caused deformation (Zhao et al.,2009; 
He et al.,2006; Xu et al.,2008 ) and co-seismic deformation 
extraction and modeling (Shan et al., 2002; Ji et al., 2009). 
Recently, Advanced D-InSAR techniques gain their use in long 
term series deformation monitoring in urban areas (Fang et al., 
2009; Li et al., 2009; Jiang et al., 2009; Huang et al., 2008). 
InSAR technique has also been used to monitor mining-induced 
subsidence, with the main squeeze being coal mining in China 
(Cao et al., 2008) in a cost-effective way due to the vast area 
influenced, which could be considered a startup and 
experimental and there’s certainly a long way to go for the 
operational use. The main reasons may consist in the limited 
data acquisition and the inherent limitation of InSAR for large- 
gradient and/or vegetated surface subsidence monitoring. 
4. GPS AND D-INSAR INTEGRATION 
Due to the unknown phase ambiguity number and the limited 
knowledge of the satellites’s position, measurements from D- 
InSAR are essentially relative ones. In order to relate these 
measurements to a reference datum, a priori information is 
required, such as Ground Control Points, absolute deformations 
from GPS or other geodetic techniques. What’s more, both 
atmospheric artifacts and orbital fringes feature high spatial 
correlation, since their correlation typically exceeds 1km. Local 
spurious components are compensated for by the double 
difference computation inherent in any Advanced DInSAR 
analysis, but regional signals affecting hundreds or even 
thousands of square kilometers can be difficult to discriminate 
without a priori information, thus justifying the 
complementariness between GPS and DInSAR data, which can 
be used in synergy to map surface deformation (Prati et al., 
2009). 
The idea of InSAR and GPS integration was perhaps first 
suggested in 1997 (Bock et al., 1997; 1998). Ge et al (1997, 
2000) proposed a DIDP approach for this integration. A 
methodology that uses Markov Random Field (MRF) based 
regularization and simulating annealing optimization was then 
proposed by Sverrir Guemundsson(2000) to unwrap InSAR 
images, obtaining a high-resolution 3-D motion field from 
combined GPS and interferometric observations. With GPS, 
MODIS and MORIS data, Li et al (Li, 2005a; Li et at., 2005b) 
produced regional water vapor model with a spatial resolution 
of 1km* 1km, which, applied to the ERS-2 repeat-pass data, 
assisted in discriminating geophysical signals from atmospheric 
artifacts. Doin et al. (2009) proposed another approach, using 
global atmospheric models (GAM), to model and remove the 
stratified tropospheric delay efficiently. 
5. DISCUSSIONS AND CONCLUSION 
D-InSAR technology has demonstrated unsurpassed capabilities 
of the technique in terms of deformation monitoring, and has 
embedded itself one of the most widely used geodesy 
techniques, combining the characteristics of large-scale imaging 
and high-accuracy quantitative observations, particularly of 
dynamic processes. However, there still exist several limitations 
at present, related as follows: 
A) Excessive subsidence (i.e., big phase gradient) taking place 
in one repeat cycle of satellite makes impossible deformation 
measurement without a priori information; 
B) A systemtic errors introduced during the D-InSAR process, 
such as caused by mis-coregistration, orbit perturbation, 
inaccurate topography model, phase unwrapping, atmospheric 
artifact, remains unknown, and the precision evaluation of the 
end-product at present only comparatively known through a so- 
called Quantitative Analysis step (i.e., making comparisons with 
respect to traditional implementation geodetic method); 
C) Characteristics of PSs, utilized in PSI techniques, require a 
thoroughly study, in order to geocode and interpret the studied 
PS deformation more accurately to the local structure; 
D) In some cases, such as the coal mining influenced area, 
where typically displacement in all the 3-D takes place, making 
subsidence not so dominating, chances are unpractical 
deforming information will be acquired. 
With the newly launched satellites and some ongoing research 
activity, the above-mentioned limitations can be addressed, to a 
certain extent at least, if not completely. For example, the newly 
launched four SAR satellites, operating at X-band, feature short 
repeat cycles: three belong to the dual-use Cosmo-SKymed 
constellation operated by the Italian Space Agency, with a 4-day 
cycle, and one is the German TerraSAR-X, with the cycle of 11 
days could make less likely excess subsidence. What’s more, 
some ongoing research activity are aiming at the study of the 
nature of PSs, and striking results have already been reported 
(Ferretti et al., 2005). With more knowledge of PSs, cross 
frequency and/or cross-incidence angle could be possible and 
extremely promising. We are surely convinced that all these 
existed and upcoming efforts will lead to an operational and 
routine use of Spacebome InSAR technology for ground surface 
deformation monitoring. 
REFERNECES: 
Arrigoni M., Colesanti C., Ferretti A., Perissin D., Prati C., and 
Rocca F., 2003.Identification of the location phase screen of 
ERS-ENVISAT permanent scatterers,” presented at the Fringe 
2003 Conf., Frascati, Italy. 
Berardino P., Fomaro G., Fusco A., Galluzzo D., Lanari R., 
Sansosti E., Usai S.,2001. A new approach for analyzing the 
temporal evolution of Earth surface deformations based on the 
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