Monitoring Global Vegetation Degradation Using NOAA NDVI Data
4. Results
Figure-3 shows the vegetation fluctuation patterns for some ecoregion categories. The tendency of GVIdynamics can be easily known from the graphs.
Figure-3. GVI Fluctuation Patterns by eco-regions categories
Table-l shows the calculated vegetation degradation index. Minus value of the index means that the tendency: of vegetation activity is declining. So the less the vegetation degradation index shows, the more the vegetation degradation is proceeding. Generally, the categories those average of GVI are low have the tendency to increase the vegetation activities, and the categories those average of GVI are high have that to decline the vegetation activities.
Table-l Vegetation Degradation Index(VDI) and categories
| VDI Categories |
VDI Categories |
| 0.33 Ice |
-0.18 Urban |
| 0.22 Semi arid rough grazing |
-0.20 Tropical savanna |
| 0.22 Sand desert and barren land |
-0.21 Open drought deciduous woodland |
| 0.21 Tundra |
-0.25 Dense droght deciduous forest |
| 0.21 Scrub desert and semi desert |
-0.31 Thorn shrub |
| 0.21 scrub desert + scattered trees |
-0.34 Equatorial tree crop |
| 0.20 Irrigated cropland |
-0.37 Tea |
| 0.20 Dwaf shrub |
-0.42 Coffee |
| 0.16 Vineyard |
-0.44 Open tropical woodland |
| 0.16 Vineyard |
-044 Open tropical woodland |
| 0.16 Temperate rough grazing |
-0.44 Equatoria rain foreat |
| ..... ...... |
-0.55 Dense evergreen broadleaf forest |
Figure-4 shows the global map of the vegetation degradation index. Large area are affected by degradation in South America, especially the central Amazon, and the LaPlata River basin, middle Africa, and South East Asia. It looks strange that the low vegetation degradation index area can be seen in Japan. The output is considered to be reasonable in the tropical regions.
Figure-4. Vegetation Degradation Index Map by eco-regions categories
5. Conclusion and Discussion
OVI fluctuation patterns could be recognized by overlaying the long-term NOM NDVI data and eco-regions map. By using the pattern graph, a vegetation degradation index was proposed which is showing the trend of vegetation degradation in global scale. However, the land degradation as well as vegetation degradation are considered to happen with area of several hectares to several square kilometers, depending on the types of degradation. So the s[spatial resolution is expected to be improved.
The index is showing reasonable output about the vegetation degradation in the tropical area where the mean
OVI is rather high, however, some part of temperate zone such as Japan is recognized as the area where the degradation is proceeding. To correct such error, statistical modification to the original OVI is recommended , to be made.
References .
-
Justice, C.O., Townshend,J.R.D., Holden,B.N. and Tucker,C.J., Analysis of phonology of global . vegetation using meteorological satellite data, INT.J. Remote Sensing, 1985, vo16, No8, 1271-1318
- Tucker,C.J.,Maximum Normalized Difference Vegetation Index Images for sub-Sahara Africa for 1983- 1985, INT.J. Remote Sensing, 1986, vol.7, No.11, 1383-1384
