summer cold in winter > less rain but concentrate > long
time Sunny day and more radiation.
• Vegetation: Grassplot is the leading vegetation,which
mainly include hilly grassland field, high-cold grassland
field and high-cold meadow field, hilly grassland field is
chiefly distributed in the plain of the north bank of
Qinghai Lake and in the edge of the south hill, and have
less distribution in the slope to sun with 3200—3500m
high-cold grassland field and with some plant such as
precarious. High-cold grassland field principally spread
in drought slope to sun of the north and middle part
coteau and small proportion of the hill, with the altitude
of 3300—3600m, and the vegetation in this region is
mainly couch grass. Sub-high-cold grassland field chiefly
distribute in the north of Gangcha and down-sun slope of
the middle coteau, with 3400—3700 altitude, in the
region of which vegetation is abundant, but the
differentiation of the community is not obvious. The
bottomland of north Molei River is the distribution of
sub-high-mountain-swamp meadow field with 4400—
4700m altitude, the arrangement of grassplot is
unconspicuous with 1.95—12.1cm height of grass and the
average bestow proportion is 71.5%. Frustex meadow
field is mainly distributed in the downsun slope of Haixi
Mountain and north hill with 3300—4500m height above
sea level, but the arrangement of grassplot is conspicuous.
• Social and economy: There are four county—gangcha^
gonghe > tianjun and haiyan. It has lager population
consistency, and more developed economy, and which is
an important pasture base of Qinghai province, and in
1986 the Qinghai Lake is authorized as the protective
natural region of state by the State Department. But since
1950s, due to the change of the climate and the activity of
the human being’s, the quality of the grass is declined and
the productivity of stockbreeding is descended in this
area, and which have grave effect on the sustainable
development in this area. The status will become worse if
nothing has been done to the Land Sandy Desertification
in this area.
• These characters have much impact of land sand
desertification on
2.2 Data
Land sand desertification is a long-term action, so we elected
Landsat MSS data collected in Oct, 1973 and ASTER LIB data
collected in Sep,2003 to do the research. The Advanced
Spacebome Thermal Emission and Reflection Radiometer
(ASTER) is an advanced multi spectral imager that was
launched on board NASA’s Terra spacecraft in December,
1999. ASTER covers a wide spectral region with 14 bands
from the visible to the thermal infrared with high spatial,
spectral and radiometric resolution. An additional backward
looking near-infrared band provides stereo coverage. The
spatial resolution varies with wavelength: 15 m in the visible
and near-infrared (VNIR), 30 m in the short wave infrared
(SWIR), and 90 m in the thermal infrared (TIR). Each ASTER
scene covers an area of 60 x 60 km. The ASTER instrument
produces two types of Level-1 data: Level-1A (LIA) and
Level-IB (LIB). ASTER LI A data are formally defined as
reconstructed, unprocessed instrument data at full resolution.
They consist of the image data, the radiometric coefficients, the
geometric coefficients and other auxiliary data without
applying the coefficients to the image data, thus maintaining
original data values. The LIB data are generated by applying
these coefficients for radiometric calibration and geometric
resampling(Mei Anxin, Peng Wanglu, et al,2001, Shunlin
Liang, 2004, Hu Peng,et al,2002).
Other than Remote Sensed data , we also elected some climate
data, topography data, social and economy data, etc.
2.3 Land Sandy Desertification Classification system
In order to simplify the classification, this paper classify the
Land Sandy Desertification to six levels as light, low-grade,
middle, high-grade, strong and Intensive. Table 1 is the
classification index of the Land Sandy Desertification.
Table 1 Classification Index of Sandy Desertification
Grade
Surface form
Vegetation
Overcast ratio
1 light
Fastness dene, sandlot and
sand beach
>70%
2 low-grade
Fastness dene, half-fastness
sandlot and sand beach
70-50%
3 middle
half-fastness dene and
sandlot
50-30%
4 high-grade
half-fastness dene, flowing
sandlot and sand beach
30-10%
5 strong
flowing sandlot and sand
beach
<10%
6 intensive
Large-area flowing sandlot
and sand beach
<5%
2.4 process flowchart
Figure 2 is the process flowchart used in the paper. We use
false color image of ASTER 3N21 and false color image of
MSS 754 for Unsupervised Classification, then with the aid of
NDVI Retrieval result, Climate data, Topography data, Social
and Economy data to do the Land Sandy Classification.
Figure 2. Process flowchart
3 RESULTS
3.1 Land Sandy Desertification in 1973 and 2000 of
Qinghai Lake Area.
Figure 3 and Figure 4 are the spatial change of Land Sandy
Desertification in 1973 and 2000 in Qinghai Lake Area.
