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0.5
970 nm 1200 nm
0.4
water content:
low
medium
high
0.3
cutaway (below)
0.2
0.1
0.0
400
600
800
1000
1200
1400
1600
1800
2000
2200
wavelength in nm
visible
near-infrared
short-wave infrared
Fig. 6.16 Canopy water content, reflectance and sensing barriers ( red columns ) due to atmo-
spheric water vapor (From Clevers et al. 2010 , altered and supplemented)
970 nm
1200 nm
0.45
0.40
0.35
water content:
low
medium
high
0.30
0.25
800
900
1000
1100
1200
1300
wavelength in nm
Fig. 6.17 Enlarged cutaway from the figure on top with changed scales showing the locations of
recommended bands for canopy water sensing and of barriers (in red ) due to atmospheric water
vapor. Either first derivatives or simple wavelength ratios based on narrow bands from within the
green framed columns should be used (Drawn from data by Clevers et al. 2008 and 2010 )
Summing up, it can be concluded that the perspectives for site-specific canopy
water sensing look good. However, canopy water sensing is not yet state of the art.
It could be practiced either in a proximal sensing mode simultaneously with other
farming operations or in a remote mode, e.g. from satellites. The proximal sensing
 
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