ciduous Conifer Forest which is the sample point of index using GVI data. The vegetation degradation affected
Figure-1. By using the moving average method, the time area are seen in South America especially in the basin ofthe
series tendency. of the vegetation activity can be seen Amazon and the La Plata, Middle Africa, and South East
without. small scattering ofthe NDVI value. Asia. There are some unreasonable spots showing vegetation
degradaion where the vegetation condition is considered to
3. METHODOLOGY be rather stable. For the future study, the modification method
to make standerdize data which include the variety ofthe
Alter preprocessing ofthe data, the characteristics of 8km sensors, and position should be considered.
NDVI fluctuation pattern can be obtained and a major pattern
is selected to represent each class. The represented patterns References
are used to reclass the existing map fromlow spatial
? resolution to 8km resolution. The new time series maps for10 — Justice,C.O., Townshend,J.R.D., Holden,B.N., and Tucker,C.J.,
: years data shows the vegetation class during the 10 years 1985, Analysis ofthe phonology ofglobal vegetation using
and the changes of vegetation map, which had not been meteorological satellite data, INT.J.Remote Sensing, Vol6,
generated with satellite data, with little ground No.8, ppl1271-1318
investigation. Tucker, C.J.,1986, Maximumnormalized difference vegetation
Index images for sub-Sahara Africa for 1983-1985,
On the other hand, the NDVI fluctuation patterns may change = INT.J.RemoteSensing, Vol7,No.11,pp1383-1384
depending on the climate conditions in cach year, however,
the long term tendency ofthe fluctuation is expected to be
stable in rather long period e.g. 10 years. Figure-3 shows
samples ofaverage "GVI" fluctuation pattern for "Tropical
Broadleaf Forest", "Equatorial Rain Forest", "Semi Desert" and
"Sand Desert and Barren Land" fromApril, 1985 to December,
1988. From these figures tendencies ofthe fluctuation
patterns which is declining, increasing or stable can be seen.
A index which is called vegetation degradation index is
proposed to indicate the vegetation degradation tendency
which is defined as the inclination ofthe line-f(x) to fit the
following formula.
0
T
y=G (x)
RS EEE ME
f (x) =ax+b
EOS
m m= 1'2n
e Figure-4 Illustration of Definition of
| Vegetation Degradation Index
J 4. RESULT AND DISCUSSION
Outcome(Slide) demonstrates how to define the degradation
tendency of GVI fluctuation pattern - G(x) - ,and line - f(x)- is
set to make the area above the line and below the line to be
Same. Points with smaller inclination ofthe tendency line is
the area where serious vegetation degradation is proceeding.
After calculation of the vegetation degradation index foreach
pixel, a map of vegetation degradation is generated. Outcome(
Slide)shows the global map ofthe vegetation degradation
549
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996