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4.06 AVERAGE PLANT PRODUCTION |
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Data ID |
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Description: |
Average maximum Green vegetation biomass between 93-94 and 99-00 seasons |
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Chapter: |
4 Living Resources |
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File name: |
gvb_9300 |
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File type: |
ArcView shapefile |
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Geographical area: |
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Keywords: |
GVB |
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biomass |
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vegetation |
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Notes on data, analysis and |
An average composite of maximum green vegetation biomass for the seasons 93-94 to 99-00. |
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compilation: |
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The Green Vegetation Biomass (GVB) images are derived from satellite data (NOAA) and represent the maximum green |
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vegetation cover and biomass during the rainy season (October to April). Every day the satellite data are recorded for |
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every pixel (1 x 1 km area) of |
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pixel are extracted and a 10 day composite image produced. Such images are also called maximum value composites |
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(MVC’s). To produce the overall rainy season GVB image, all of the 10 day MVC’s are compiled and the maximum |
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values of each pixel are extracted. |
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The rainy season GVB values therefore represent the maximum values during the entire rainy season for any location in |
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Namibia. Such images are very useful indicators of possible drought conditions which may occur in the dry season, and |
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could identify areas for selective drought aid distribution. These images also show areas with normal or high vegetation |
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development, which may guide farmers in dryer areas to move their stock to these high biomass areas during the dry |
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season if possible. |
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A study in Etosha during 1994/95 compared MVC values with green vegetation cover and biomass and with 10 day |
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interval rainfall as well as with annual rainfall. The Etosha Pan is a relatively constant reflective source, and has been |
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used as a calibration constant since 1993. From this study, the Green Vegetation Biomass (GVB) concept has been |
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developed, and a classification system proposed. The images have been classed into 12 classes. This process involves |
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grouping the digital number (DN) values ranging between 0 and 255 into 12 classes. |
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The first class (DN 0-10) represents water. |
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The second class (DN 11-50) represents water, clouds or bare ground. |
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The third class (DN 51-110) represents bare ground or extremely low GVB development (the Etosha Pan typically |
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belongs to this class). |
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The fourth class (DN 111-125) represents very low GVB development. |
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The fifth class (DN 126-140) represents low GVB development. |
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The sixth class (DN 141-155) represents medium GVB development. |
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The seventh class (DN 156-170) represents high GVB development |
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The eighth class (DN 171-185) represents very high GVB development. |
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The ninth class (DN 186-200) represents extremely high GVB (level 1) development. |
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The tenth class (DN 201-215) represents extremely high GVB (level 2) development. |
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The eleventh class (DN 216-230) represents extremely high GVB (level 3) development. |
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The twelfth class (DN 231-255) represents extremely high GVB (level 4) development. |
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The range of values between extremely low to extremely high level 4 GVB have been quantified in terms of grass cover |
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and biomass: |
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Description Percentage cover Grass standing crop/biomass |
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Extremely low cover or standing crop/biomass 0-1 % 286 kg ha-1 |
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Very low 1-5% 287-628 kg ha-1 |
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Low 5-25% 629-1235 kg ha-1 |
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Medium 25-50% 1236-2032 kg ha-1 |
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High 50-75% 2033-3020 kg ha-1 |
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Very high 75-90% 3021-4197 kg ha-1 |
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Extremely high level 1 to 4 90-100% > 4197 kg ha-1 |
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Class 1 and 2 are of little concern to vegetation studies. Class 3 represent bare ground, no green vegetation or extremely |
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low levels of green vegetation development. Most game, domestic stock and people are not be able to make a living |
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from the land during the subsequent dry season in such areas. |
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Note: with the shapefiles, polygon values represent the classes described above (first class = 1, second class = 2 etc.) |
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although some of the classes have been amalgamated. For interpretation see the Arcview legend file supplied. The |
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shapefile was created following resampling (0.025 cell size) of the grid file. |
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Data quality and organisation |
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Positional Accuracy: |
Derived from 1x1 km grid (NOAA image) |
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Vector/Raster: |
Vector |
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Spatial reference |
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Projection: |
Geographic |
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Fields |
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Field name |
Field description |
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GRIDCODE |
polygon values represent the GVB classes described in the notes |
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(first class = 1, second class = 2 etc.) although some classes have |
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been amalgamated. 2 = bare ground, 3 = VL, 4 =L , 5 = M, 6 = H, 7 |
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= VH, 8= EH1, 9 = EH2-4 |
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COUNT |
Number of polygons in the GVB class |
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Source/Distribution |
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Data Source: |
Wynand du Plessis |
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Distribution notes: |
Unrestricted |