133 
determined by ground objects’ texture characteristics with little 
influenced from water (ice). The vegetation on the alpine aim is 
denser than on the alpine meadow, and conglomerates on the 
alpine aim have higher density, so the coherence of alpine aim 
is higher than of alpine meadow. 
Figure 4. Influence on coherence of part area season thawing. 
The images, composing pair C or D, are obtained at the time 
between the end of January and the beginning of March and 
April respectively, and this period belongs to the process of 
temperature rising in spring. In the pair C, when the 
temperature is rising in March and April, alpine aim firstly 
begins to thaw because of more density vegetation and energy 
exchange, and the scattering characteristics correspondingly 
take place change that leading to decorrelation. However, alpine 
meadow still keeps in lower temperature, so the coherence of 
ground objects on alpine meadow varies little. The phenomena 
presented above results that alpine aim has little lower 
coherence than alpine meadow. In April, with the temperature 
rising further, frozen ground in the region of alpine aim thaw 
strongly and the coherence decrease continually. However, 
frozen ground in the region of alpine meadow has not began to 
thaw and the coherence in alpine meadow still keep high value 
relatively. So, there is a big difference on conherence between 
alpine aim and alpine meadow in the pair D. 
Table 1. Comparison of coherence for different process of 
frozen earth changing 
ID 
Date 
Whole 
Railwa 
y 
A 
041118-041223 
66 
0.431 
0.340 
0.206 
0.157 
D 
050127-050407 
-185.4 
0.335 
0.335 
0.175 
0.133 
H 
040108-040527 
-14.4 
0.283 
0.176 
0.152 
0.091 
K 
040527-041014 
18.6 
0.174 
0.176 
0.112 
0.097 
O 
050407-060216 
53.8 
0.198 
0.143 
0.115 
0.090 
The two images, composing the pair H, are acquired at the 
beginning of January and the end of May. At the end of May, 
all near-surface of permafrost in Beiluhe area enter upon the 
process of thawing with the temperature rising, and the change 
from thawing phenomenon is same to all the ground objects, so 
ground object characteristic becomes the main factor that 
influences the coherence again in Beiluhe area. 
To analyze the coherence characteristics for different 
thawing/ffeezing process at all permafrost area, we select 5 
interferograms to compare the coherence coefficients. Tab. 1 
list the coherence coefficients and perpendicular baseline for 
the 5 pairs. 
Comparing the pair A and H, it can be found that the pair H has 
shorter spatial baseline but lower coherence than the pair A for 
all kinds of ground objects. The two images, composing the pair 
A, are both acquired in winter. On the contrary, the two images, 
composing the pair H, are not acquired in the same season. One 
is acquired in the stable winter, and the other is acquired at the 
active process on April. In other words, the pair H experiences 
the process of frozen ground thawing, so the ground objects’ 
dielectric characteristics have an evident change and coherence 
falling correspondingly. This means that the coherence is 
affected by the thawing process. 
With regard to the pair H and the pair K, the value of two pairs’ 
spatial baseline is very close, but their coherence has a great 
difference and the coherence of the pair H is much higher than 
that of the pair K. Comparing the time of image acquired for 
two pair, we can find that the pair H is from a stable statue to an 
active statue and the pair K goes through two active process 
which are thawing and freezing, so in the pair K ground surface 
change a lot and the effect of decorrelation is more strong. 
Both the pair O and the pair D experience the process of 
thawing and freezing, but the pair O goes through all 
thawing/freezing circle in almost one year interval. The 
coherence of the pair O is lower than that of the pair D, which 
means that ground surface has seriously decorrelated after the 
process of thawing and freezing, even the ground surface goes 
back to the stable status again. 
5.2 Deformation Analyzing of PS 
Whenever enough images are available, DInSAR limitations 
can be overcome by adopting a multi-interferogram framework. 
The PS technique takes advantage of long temporal series of 
SAR data, acquired over the area of interest along the same 
(nominal) satellite orbit, to filter out atmospheric artefacts and 
to identify a subset of image pixels where high-precision 
measurements can be carried out. These pixels, almost 
unaffected by temporal and geometrical decorrelation (usually 
but not necessarily corresponding to man-made objects) are PS 
(Colesanti, 2003; Bu'rgmann, 2006). 
There are 385 points were selected as PS in experiments area 
with 12 interferograms between Jan. 8, 2004 and June 1, 2006, 
a lot of PS are around the Qinghai-Tibetan railway and highway 
passing Beiluhe area. Figure 6 showed the PS candidates 
distribution around the railway and highway. There are two 
lines interlacing with each other in these images, the left one is 
the Qinghai-Tibetan railway, and the right one is the highway. 
The deformation history of PS are derived from 12 
interferograms after removed the topographic phase and the 
effect from atmosphere and orbit errors. Fig.7 showed the 
deformation value for different time period compared with Jan. 
27, 2005 around Qinghai-Tibet railway area. The maximum