In: Wagner W., Székely, B. (eds.): ISPRS ТС VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Vol. XXXVIII, Part 7B 
and then to Mt. Dahingganling, Mt. Xiaohingganling and Three 
River Plain (also known as the Sanjiang Plain). This 
progression is disrupted by the high elevation of Mt. Changbai. 
The onset of near-surface soil frozen begins early in the Gurban 
Tonggut and Taklimakan deserts, which can perhaps be 
attributed to these areas being at lower elevations than 
surrounding areas and having less soil water. 
The earliest offset of near-surface soil frozen occurs at Mt. 
Qinling. It then progresses to the northwest through the 
Guanzhong Basin, along the west of the Loess Plateau, through 
the Hexi Corridor and Badain Jaran Desert, and finally to Mt. 
Altayn and Mt. Hangayn. To the east of the Badain Jaran Desert 
and Hexi Corridor, the offset of near-surface soil frozen arrives 
earlier than in surrounding regions. From Mt. Qinling, the offset 
progresses north to the Guanzhong Basin, and continues along 
the area south of Mt. Luliang and Mt. Taihang, then to the 
Loess and Ordos plateaus and through to Mt. Yinshan, the 
Mongolian Plateau, and the Desert Basin, until the latest offset 
of near-surface soil frozen occurs on the Hulunboir Plateau and 
at Mt. Henteyn. The offset of near-surface soil frozen also 
progresses northeast from the Haihe River Plain along the coast 
to the Horqin Sandy Land, and then to the surrounding areas of 
Mt. Dahingganling, Mt. Xiaohingganling, the Northeast Plain, 
Mt. Changbai, with the latest offset of near-surface soil frozen 
occurring to the north of Mt. Dahingganling and the Three 
River Plain. 
Figure 3. Onset (upper) and offset (nether) of springtime soil thaw derived from SSM/I brightness temperature (Julian week). (Gray- 
colored areas are the high elevation regions) 
5.4. Difference in the results 
Result that derived from SSM/I brightness temperature was 
almost relied on the T 37 which have significant linear 
relationship with near-surface soil temperature. From which, we 
can deduce that the results derived from SSM/I brightness 
temperature is sensitive to near-surface soil temperature, which 
is why soil thaw event could be detected in desert regions. 
Result that derived from QuikSCAT backscatter time series has 
regions both soil thaw event occurrence and no soil thaw event 
occurrence. From the analysis of average air temperature and 
modeled soil moisture as shown in figure 4, the difference 
between samples with/without soil thaw event happened could 
be clarified: 1) samples with thaw event detected by QuikSCAT 
backscatter had an average air temperature of -15.29±4.29 °C 
with soil moisture of 38.27+21.96 mm in the month of thaw 
event happened; and 2) samples without thaw event detected by 
QuikSCAT backscatter had an average air temperature of - 
1.80+6.37 °C with soil moisture of 35.77+24.63 mm in the 
month when air temperature switch from negative values to 
positive values. And at the areas where air temperature keeping 
negative for a long period but no thaw event detected could 
easily deduce that the region has no enough soil water content 
to freeze.