The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008
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3.3 Establishment of a regression model
For the establishment of a regression model the correlation
between the VI and agronomic parameter from the experiment
field data from 2006 have been tested by coefficient of
determination (R 2 ). Generally the correlations are dependent on
the winter wheat variety and GS. For the analysis four different
feekes GS (4, 5, 7 and 9) were used. The analysis show that
correlations between hyperspectral Vis and agronomic
parameters are higher as for multispectral Vis. Significant
correlations could be made for biomass, N-content, N-uptake,
SPAD and measured LAI for the experiment fields. N-uptake
was calculated as the product from dry biomass and N-content.
Biomass and plant N-uptake show the highest R 2 values for
HNDVI, HVI, OSAVI and MCARI2 for the experiments fields.
SPAD readings were only significant for the GS 4, but not for
other GS or across all stages. The chlorophyll content decreases
during the stages 4 to 9, so that this parameter is disregarded for
the use in a model. The R 2 for LAI and the VI also show
different significant and not significant correlations for the tree
experiments. An establishment of a model for LAI is not
possible with the 2006 data.
Results for multispectral Vis like the NDVI in this study are
evaluated in Li et al. (2008). Analysis from Koppe et al. (2008)
show that Normalized Ratio Indices (NRI) derived from a large
number of two-bands combinations of EO-1 ALI and Hyperion
satellite images offer good results
3.4 Model evaluation
In this step the data are analysed for model evaluation. Thereby
the data of the farmer's field from the two years 2006 and 2007
are validated. For 2006 the GS 4, 5, 7 and 9 have been
considered and for 2007 GS 4, 5 and 7. Table 2 shows the
coefficient of determination (R 2 ) for the agronomic parameters
like biomass, plant N-uptake and LAI and selected VI. Plant-
uptake and biomass show the highest R 2 values for all Vis.
HNDVI and OSAVI are more significant as NDVI and other VI
for the four stages and across the stages in 2006. Correlations
for LAI can be stated only for two feekes GS. Regarding the
analysis of 2007, the performance of the regression models is
less reliable than in the 2006 analysis as the R 2 values are lower.
Especially the R 2 values for OSAVI at the feek GS 4 and 5 are
lower as for RVI or NDVI. So in 2007 the models for RVI show
the best performance for the feekes GS 4 and 5, OSAVI for the
GS 7 and across all stages calculations of OSAVI and HNDVI
provide best results
NDVI
RVI
HNDVI
HVI
OSAVI
MCARI2
Feekes growth stage 4, n = 74
biomass (kg/ha)
0.629***
0.603***
0.665***
0.518***
0.656***
0.567***
Plant N-uptake (kg/ha)
1 0.710***
0.707***
0.752***
0.716***
0.727***
0.532***
Feekes growth stage 5, n - 43
biomass (kg/ha)
1 0.323*
0.323*
0.318*
0.160
0.313*
0.239*
plant N-uptake (kg/ha)
1 0.390**
0.391**
0.330*
0.305*
0.445**
0.393**
Feekes growth stage 7, n = 43
biomass (kg/ha)
0.107
0.101
0.123
0.034
0.115
0.086
VO
o
plant N-uptake (kg/ha)
I 0.294*
0.290*
0.308*
0.176
0.357*
0.304*
o
N
LAI
0.077
0.081
0.088
0.193
0.182
0.222
Feekes growth stage 9, n = 43
biomass (kg/ha)
1 0.104
0.101
0.126
0.099
0.156
0.119
plant N-uptake (kg/ha)
0.130
0.124
0.129
0.149
0.202
0.181
LAI
1 0.148
0.152
0.296*
0.300**
0.389**
0.357**
All growth stages n=
203, n = 86 for LAI
biomass (kg/ha)
I 0.583**
0.603**
0.609**
0.441**
0.620**
0.525**
plant N-uptake (kg/ha)
I 0.593**
0.618**
0.618**
0.449**
0.631**
0.532**
LAI
1 0.114
0.112
0.149
0.115
0.239*
0.203*
Feekes growth stage 4, n = 95
biomass (kg/ha)
I 0.407***
0.443***
0.410***
0.054
0.229**
0.289**
plant N-uptake (kg/ha)
1 0.351***
0.333**
0.349**
0.082
0.241**
0.299**
Feekes growth stage 5, n = 52
biomass (kg/ha)
H 0.323*
0.358**
0.342*
0.151
0.302*
0.379**
t"
©
plant N-uptake (kg/ha)
0.390**
0.301*
0.292*
0.111
0.270**
0.454**
©
fN
Feekes growth stage 7, n — 50
biomass (kg/ha)
J 0.044
0.037
0.051
0.101
0.114
0.131
plant N-uptake (kg/ha)
1 0.023
0.013
0.022
0.031
0.049
0.138
All growth stages, n = 197
biomass (kg/ha)
j 0.583**
0.603**
0.609**
0.441**
0.620**
0.525**
plant N-uptake (kg/ha)
0.593**
0.618**
0.618**
0.449**
0.631**
0.532**
* significant at 0.05 level; ** significant at 0.01 level; *** significant at 0.001 level
Table 2. Correlations coefficients for relationships between agronomic parameters and Vis for farmer’s field