ypes 
and 
‚use 
ugh 
ind 
[oT 
0 
xels area at 
546 8736 
84 1344 
132 2112 
) 
+ 
1000 à 
  
  
„10 
of 
.) and 
    
The influence of vigor conditions on the spectral signatures can 
clearly be recognized here where healthy maize is compared with 
maize affected by drought. The decrease of the reflectance in the 
IR part of the spectrum is well described in the literature but 
it is remarkable that the reflectance increases in the visible 
part of the spectrum, not only in the red part, but also in the 
green part of the spectrum, which cannot be realized visually. 
The observation zenith angle has proved to be a very important 
factor influencing the spectral response of the objects. An 
example of a deciduous forest is given in figure 7. 
The changes of the reflexion behaviour depending on the obser- 
vation zenith angle can be clearly seen in figure 8 which shows 
the relative change of the energy measured in chanel 10 of the 
MSS for a pine stand. The azimuth angle difference between the 
observation and the sun direction has been kept either 09 or 
1800 in this curve or 909 and 270. respectively. This leads to 
the recommendation that scanner flight missions should be per- 
formed in such a way that an azimuth angle difference of 90 and 
2709, respectively, should be applied in order to avoid 
difficulties in recognizing the objects. 
The energy reflected from the object will be changed by passing 
through the atmosphere as demonstrated in figure 9 (10). There 
are two effects which cause this variation: the first one is the 
overlying of scattered light on the reflected energy which 
dominates in the visible part of the spectrum. The second is 
the extinction which dominates in the IR part of the spectrum. 
  
  
  
  
  
  
>> 1. corn, healthy 
Mee oM z ----seseeas LAUDMALD Theta r=38 Phi r=229 
2. corn, affected by. |  .....---- LAUDVALD Theta r=0 Phi r=0 
drought Le sgu4o,m.= LAUDNALD Thota r=12 Phi r=49 
--.--.-- .-- LAUBWALD Theta r=5 Phi rzh9 
Theta 1 289. 
Theta r Phi r Phi i 159° (-21%) 
13 229 
2. 13 229 
Theta i 28° o 
Phi i 1599 (-21?) 
es R X 4 
60 + $0 1 
so A so 
-* | --——— 
az ; 4 eere 
^ ! as areas? 
so + / | so M memmates 
4 | >”, 
vr | Je , 
20 4 = 20 
| | E 
i | f 
3 | i/ 
i01 — "+++ ; ' | 10 i 
ar hala ed , 
= | Sra] 
——————— M 
400 500 600 700 800 300 1000 à ! ado Goo 400 100 0d 100 1009 3 
ce aan ea e s | s tennes 2 € 
CH. NM 3823332323 5 2 | CH. NM a3$252225238 à a 
7 
CH. NO 12345678 19 10 | CH. NO. 12345678 3 10 
  
  
  
  
Fig. 6 Spectral Signatures of corn Fig. 7 Spectral signatures of a deciduous 
(healthy and diseased) fores und different observation angles