Land degradation & change detection of biophysical products using multi temporal
SPOT NDVI image data:a case in Blue Nile river basin, Ethiopia
Taye Gidyelew
International Livestock Research Institute (ILRI)
Introduction
Land degradation is a process of progressive deterioration of biological and physical resources of the land
It is a cause of low agricultural productivity for Sub–Saharan Africa in general and Ethiopia in Particular.
Biophysical products such as NDVI,NPP and biomass indirectly determines land degradation
Intro…
Remote sensing is the best method for obtaining such data
Recently large volume of high quality global remotely sensed data available
– SPOT– MODIS– MERIS– AVRIS/NOAA
Objective of the study
To identify the trend of NDVI to monitor land degradation through analysis of multi temporal and multi spectral SPOT-Vegetation imageries and
To determine the amount of Net Primary Product (NPP) and fraction of Absorbed Photosynthetically Active Radiation (fAPAR) in Blue Nile river basin.
Methodology - study site
Clip NDVI to sample land
use
DN NDVI Image From Spot Satellite
Conversion NDVI
Image to Arcinfo grid
and dbf
Decadal NDVI
to monthly NDVI
Determine & stratifiy
Land use types
7 years NDVI
Trends per land use types
Landsat imageries
(1999&2003)
Woody Biomass land cover
Yearly and Monthly
NDVI
Methodology
Algorithms to derive biophysical products
Normalized Difference vegetation Index (NDVI)
REDNIR
REDNIRNDVI
fAPAR = a + b *NDVI fAPAR= -0.025+1.25*NDVI
• Fraction of Absorbed Photosynthetically Active Radiation (fAPAR)
Algorithms……
Net Primary Productivity (NPP)
PARdt*fAPARNPP
12
1
0.798] / 0.087)* (NDVI * NDVI) * 1.25 (-0.025 * [1.5NPP
Results and discussion
The biophysical products are derived from the SPOT vegetation for different LU types which are:
– Dabus Valley park– Farm land– Forest area– Grass land and– Towns
Dabus Valley Park_ NDVI
y = -0.0128x + 0.4758
0.00
0.20
0.40
0.60
1998 1999 2000 2001 2002 2003 2004
Years
ND
VI
MIN
MAX
MEAN
Farm land_ NDVI
y = -0.0076x + 0.4238
0.00
0.20
0.40
0.60
1998 1999 2000 2001 2002 2003 2004
Years
ND
VI
MINMAXMEAN
Forest area_NDVI
y = 0.0002x + 0.4693
-0.10
0.10
0.30
0.50
0.70
1998 1999 2000 2001 2002 2003 2004
Years
ND
VI
MINMAXMEAN
Grassland_NDVI
y = -0.001x + 0.3948
0
0.2
0.4
0.6
0.8
1998 1999 2000 2001 2002 2003 2004
years
ND
VI
MIN
MAX
MEAN
Town-NDVI
y = -0.0045x + 0.4046
0.00
0.10
0.20
0.30
0.40
0.50
0.60
1998 1999 2000 2001 2002 2003 2004
Years
ND
VI
MinMaxMean
NDVI for all land use types
0.30
0.40
0.50
0.60
1998 1999 2000 2001 2002 2003 2004
Dabus
Farm
Forest
Grass
Town
The NDVI for town is appeared at the bottom of all curves followed by that of grass land and forest at the top of all
Overall monthly NDVI for all Land use types
0
0.2
0.4
0.6
0.8
98
04
'
98
07
'
98
10
'
99
01
'
99
04
'
99
07
'
99
10
'
00
01
'
00
04
'
00
07
'
00
10
'
01
01
'
01
04
'
01
07
'
01
10
'
02
01
'
02
04
'
02
07
'
02
10
'
03
01
'
03
04
'
03
07
'
03
10
'
04
01
'
04
04
'
04
07
'
04
10
'
DabusFarmForestGrassTown
Time
NDVI
Summary of fAPAR and NPP
Land Use Mean NDVI fAPAR NPP Remark
Dabus 0.4245 0.5056 5.98
Farm land 0.3936 0.4670 4.64
Forest 0.4702 0.5627 6.36 Highest
Grass land 0.3909 0.4636 4.61
Town 0.3868 0.4585 4.42 Least
Conclusion and Recommendation
The NDVI trend and the derived parameters during the seven periods time showed a declining trend .
Forest area over the study area showed higher value for all the biophysical products and a minimum value is recorded in towns.
Combination of Rain Use Efficiency with NDVI trends will be a good parameter to monitor the status of vegetation cover and good indicator for land degradation.
Field data has to be included for validation and calibration of biophysical products for different land use types
Thank you !
Comments, suggestions and questions are most welcome!
Land cover Land use 15 years ago