3-3. Effect of Viewing angle on Canopy Spectral Radiance Factor for 
Paddy fields 
    
   
  
  
  
  
   
  
   
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
  
   
  
  
  
  
  
  
  
  
  
    
As the data acquistition of the remote sensing are mainly done 
in the center projection, it is required to make clear the relation 
between the viewing angle and the characteristics of the spectral 
radiance of the object. 
The effect of the change of the viewing angle was measured with 
the rotating mirror with the fixed spectro-radiometer. (Fig.3-6,3-7) 
The mirror rotates from +45 to -60 degree by 15 degree in vertical 
observation. This rotating mirror was used to get a long observation 
distance and to measure the large area of canopy by the spectro 
radiometer with the small viewing angle. 
Fig. 3-8 shows the differences of the mirror images of the canopy 
according to the chage of the observation angle. 
When the automatic spectro-radiometer had used, the observation 
area of radio is ll cm with the 2? FOV and with 6 m observation distance 
was measured. 
The measurement was carried out with the average of the 3 or 5 
data which were given from the random point on the mirror while the 
Kodak white standard board on the same hight with the canopy was 
also measured. During the measurement, it was cloudy sky and the 
light source can be considered as the perfect distributed one. 
Fig. 3-9,- 3-15 shows the change of the spectral radiance factor 
according to the change of the viewing angle, where the spectral 
radiance factor was expressed with the relative value g, Q7 geh) - 
As the rice stump grows straightly to the end of ripping period and 
the each leaf stands straightly, Stove-pipe Effect was observed (Fig.3-9, 
Fig. 3-15). Especcially this effect was clear before the blooming 
season, but it got smaller after the blooming season to the ripping 
period and disapeared at the end of the ripping period. (i.e. had 
a deffuse feflectance). 
And this effect was remarkable in the Infra-red band rather 
than in the visible bands. 
The viewing angle which gives the minimum radiance factor 
8 (\) depends on the bending direction of the rice which mainly affected 
by the wind blows there. In Fig. 3-9 - Fig. 3- 15, the minimum value 
were given when the angle is -15° - +15°. This phenomenon was also 
clear judging fmem the change of the photographs is Fig. 3-8.