SPECTRAL T1 BL D MEASUREMENTS 
FOR THE DETERMINATION OF 
REFLECTANCE CHARACTERISTICS 
OF VEGETATED SURFACES 
             
      
      
   
     
     
   
      
      
       
      
   
   
    
    
    
      
   
   
   
    
    
      
    
     
      
           
     
H.-J. Boehnel, W. Fischer, G. Knoll 
Institut fur physikalische Weltraumforschung 
D-7800 Freiburg, Heidenhofstrasse 8, Fed. Rep. of Germany 
Introduction 
   
Many applications of remote sensing techniques are based 
on the concept of multispectral discrimination. In the 
visible and the near infrared part of the electromagnetic 
radiation spectrum the spectral characteristics of objects 
depend on their reflection properties. Natural targets 
are commonly not flat and homogeneous surfaces. The 
reflected radiation shows an anisotropic distribution of 
energy and varies with the irradiation of the scene, its 
general state and specific structure, certain environmental 
factors, etc. 
For a better understanding of the reflection properties of 
vegetated surfaces we are carrying out systematic field 
measurements with spectroradiometers in the wavelength 
range from O.4 to 2.5 um. These measurements are performed 
at different zenith angles of observation and various solar 
positions. This paper describes the methodology, the in- 
strumentation and some of the results of this investigation 
which is sponsored by the Federal Ministry of Research and 
S 
s or Technology. 
Methodology 
The geometry of reflection is shown in Figure 1. The sub- 
scripts i and r denote the 
zm incident and the reflected 
radiation, respectively. d@ 
is the element of the radiant 
ser power propagating within the 
element of solid angle dn. 
The zenith angles A} are 
angles from the reflection 
plane normal, the azimuth 
     
   
Reflexions - 
- 2 SHE pm angles ÿ are angles from an 
e : . : 
Paw. arbitrary reference direction 
in the reflection plane 
(South has been taken in the 
following.)