The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
84 samples were selected from FVC image and reference image 
of Kai County respectively (Fig.2), and the statistic numbers of 
these samples were shown in Tab. 1.The mean square deviation 
was calculated by the formula: 
a = *i(Vi-V,if !(„-1) 
Where Vi is the retrieval value, VOi is the reference value. By 
this equation the mean square error was less than 17%, that is to 
say, FVC can be obtained from MODIS vegetation indices with 
accuracies lower than 83% in the TGRA. 
4. RESULTS AND DISCUSSIONS 
The methodology described above was applied to the NDVI 
data from MODIS images to create the annual FVC images 
from 2000 to 2006 in the TGRA. Fig. 3 showed us the retrieval 
images in 2000 and in 2006 (limited by paper length, the other 
five retrieval images were omitted). From these pictures we can 
see there was no obvious change in this area in our study time. 
To study the change between different vegetation cover types, 5 
classes were divided by the threshold value of FVC images. 
They are no vegetation cover (NC) by FVC less than 0.2, low 
vegetation cover (LC) by 0.2<FVC<0.45, medium vegetation 
cover (MC) by 0.45<FVC<0.75, high vegetation cover (HC) by 
0.75<FVC<0.9, and full vegetation cover (FC) by FVC more 
than 0.9. 
(b) 
Fig.3. Illustration of the vegetation fraction maps of the Three 
Gorges Reservoir Area in 2000 and in 2006: (a) Vegetation 
fraction map in 2000; (b) Vegetation fraction map in 2006. 
4.1 Feature value change analysis of vegetation coverage 
Monitoring results from Landsat TM and MODIS imagery 
showed us that there was no obvious change on the vegetation 
cover during 7 years from 2000 to 2006 in this area (see Fig. 3c 
and 3d), but overall trend was that there was a slight decrease in 
the area of cropland, woody land and grassland, compared to a 
little increase on the averaged vegetation cover per pixel (Tab. 
1). The mean vegetation cove fraction was 0.761 in 2000 while 
0.769 in 2006, with an increase of 0.8% in the seven years. 
Usually, the regions where there were vegetation cover changes 
were construction areas and the areas with rapid economic 
development, such as the dam area, Fengjie County, Yunyang 
County, Kai County, north of Fuling, middle of Chongqing city, 
south of Jiangjin city, etc. 
Year 
minimum 
maximum 
avergae 
Mean 
square 
error 
2000 
0.074071 
0.907299 
0.761144 
0.067085 
2001 
0.100025 
0.914586 
0.749200 
0.070722 
2002 
0.065377 
0.912588 
0.770832 
0.065433 
2003 
0.057644 
0.930441 
0.779378 
0.068252 
2004 
0.067976 
0.921937 
0.783044 
0.073894 
2005 
0.085229 
0.903025 
0.764458 
0.072537 
2006 
0.096957 
0.915866 
0.768665 
0.072578 
Table 1. Feature values of FVC images from 2000 to 2006 
4.2 Grade change analysis of vegetation coverage 
The vegetation coverage in TGRA was being converted from 
NC to LC or from MC to HC (Tab. 1). The ratio of HC area was 
increasing with the number 68.7% in 2000 to 72.5% in 2006. 
The reasons are various. Increasing of water areas and 
construction lands caused by the Three Gorges Project 
construction and resettlement, reduced vegetation coverage area, 
however, implementation of a series of relative environment 
protection, such as several important forest projects of de 
farming and reforestation, mountains closed for afforestation, 
Yangtze River Forest Protection Project, greenbelt construction 
in the reservoir, increased the fraction of pixel vegetation 
coverage. 
5. CONCLUSIONS 
From the results of the vegetation cover fraction retrieved from 
time series Modis NDVI data of the TGRA, it can be concluded 
that: 
(1) It is proved to be effective that yearly vegetation cover 
information was achieved by monthly vegetation cover fraction 
using MODIS NDVI data from April to October. 
(2) The vegetation cover was increasing in a small extent in the 
Three Gorges Reservoir Area in recent seven years, with the 
average vegetation cover fraction from 0.761 in 2000 to 0.769 
in 2006. In general, the vegetation cover took on a good 
developing state. 
(3) The vegetation cover types were transformed from NC to 
LC and from MC to HC. The proportion of HC was enhanced 
from 68.7% in 2000 to 72.5% in 2006. In a word, the vegetation 
cover has been improved in recent seven years.