Agriculture Reference
In-Depth Information
winter-wheat
winter-barley
0.8
0.71
0.70
0.69
0.64
0.6
0.57
0.53 0.53
0.52 0.52
0.50
0.46
0.45
0.4
NDVI
NDVI
NDVI
NDVI
REIP
REIP
REIP
REIP
0.2
SAVI
SAVI
SAVI
SAVI
0
32
49
32
49
growth stages in EC or in BBC
Fig. 9.20
Coefficients of determination (r
2
) of standard indices for the nitrogen uptake of small
grains. The results are based on reflectance measurements by handheld instruments, natural illumi-
nation and vertical view directions.
REIP
red edge inflection point,
SAVI
soil adjusted vegetation
index,
NDVI
normalized difference vegetation index (Drawn from data by Schmid and Maidl
2005
)
results that were obtained at Munich University in Southern Germany (Fig.
9.20
). The
red edge inflection point was based on the approximating formula as defined above.
However, the coefficients of determinations of the same reflectance indices in Fig.
9.20
differ more than those listed in Table
9.3
.
The ratio of near-infrared to green is not listed in Fig.
9.20
, though this index too
provided good results that were not much inferior to those of the red edge inflection
point (Schmid and Maidl
2005
).
9.4.2.1
Interfering Factors with Standard Indices and Natural Light
Main factors that can interfere with the reflectance are the soil-colour, the zenith-
angle of the solar radiation (Fig.
9.21
) and eventually cloud-covers. Which of
these factors are important, depends on the illumination that is employed for
creating the reflectance. If natural illumination is used - which is the rule for
remote sensing and also sometimes the choice for proximal sensing - all three
factors that are mentioned above are important. When artificial illumination
induces the reflectance with proximal sensing and hence the zenith-angles of the
sun as well as cloud covers become unimportant, it is only the soil-colour that
might interfere.
