Agriculture Reference
In-Depth Information
Table 6.2 Spectroscopic sensing of water content of crop canopies (results listed by coefficients
of determination r 2 )
Plant species,
sensing methods
Reflect. indices R
with wavelength in nm
Coeffic. of
determinat. r 2
Reference
Jones et al. ( 2004 )
Maize
R1450
0.67
( Zea mays )
R2250
0.61
Sensing in the lab
Spinach
R960
0.94
( Spinacea oleracea )
R1150 - 1260
0.93
Sensing in the lab
R1450
0.85
R1950
0.80
R2250
0.79
Penuelas et al. ( 1993 )
Gerbera, 3 varieties
R970/R900
0.79
( Gerbera jamesonii )
R970/R900
0.86
Sensing in the lab
R970/R900
0.84
Sims and Gamon ( 2003 )
Means of 23 species,
R960
0.75
Sensing in the field
R1180
0.81
Sonnenschein et al. ( 2005 )
Wheat
R900/R970 static a
0.90
( Triticum aestivum )
R900/R930 - 990 var b
0.90
Sensing in the field
Wheat
R900/R981
0.90
( Triticum aestivum )
Airborne sensing
Yang and Su ( 2000 )
Rice
R697
0.81
( Oryza sativa )
R1508
0.90
Sensing in the field
R2113
0.96
a Denumerator and denominator static as listed
b Denumerator static, denominator was varied between R930 and R990
The wavelengths of the successful narrow band indices are located in a rather
wide range extending from 697 to 2,250 nm, thus within the near-infrared region
(700-1,300 nm) and the short-wave infrared region (1,300-2,500 nm). Within the
whole spectrum, the near-infrared radiation has the highest foliar reflectance due to
scattering in the canopy, and the short-wave infrared region has ranges of high
liquid water absorption. But it is not clear whether these special properties of
liquid water are important. High coefficients of determination can be seen in the
near infrared- as well as in the short-wave infrared region (Table 6.2 ). However,
sensing in the near-infrared is less expensive because these sensors are mass-produced
and less sensitive to temperature.
Generally, it can be expected that ceteris paribus sensing in laboratories provides
higher accuracies than proximal sensing in fields while remote sensing from satel-
lites or aerial platforms supplies the least precise results. However, such an effect of
the sensing location is not indicated by the coefficients of determination in Table 6.2 .
This probably is due to the fact that just comparing results from several investiga-
tions - among them many varying factors such as e.g. plant species, wavelength,
 
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