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REFLECTION TERMINOLOGY FOR REMOTE SENSING, APPLICATI 
K.T. Kriebel 
Field measurements of reflection, i.e. outside the 
are accompanied with hemispherical illumination or 
The reflected radiation is generally measured with 
ment having either a rather small field of view to 
less directional reflection quantities or a large f 
        
   
   
  
   
   
ONS 
laboratory, 
irradiation. 
an instru- 
get more or 
ield of view 
approaching the hemisphere to get the overall reflected radia- 
tion. That is the reason why the usual measuring situation, where 
the reflected radiation is measured from a small or a large finite 
cone is pressed either into the directional extreme or into the 
hemispherical extreme. 
At least for the directional measurements this procedure is belie- 
ved to be inadequate because the resulting reflection properties 
depend on the angle of view of the instrument over 
are averaged. It makes a difference whether the angle of view of 
which they 
the instrument is 1 mrad or 100 mrad, but usually both measure- 
ments are called directional and are compared to each other as 
if they were made with the same instrument. That is the main rea- 
son why we recommend to give up the directional geometry and to 
use the conical geometry which will probably be better suited to 
remind investigators to specify the angle of view of their instru- 
ments to make comparisons of results more reliable. 
Another reason to do so is the terminology. The directional re- 
flection quantity in use is usually denoted in two 
differen 
ways. It is either called (reflection) radiance factor (CIE , 
DIN , Kopdratyev ) or directional reflectance factor (Nicodemus 
IAMAP/RC’). Because it is still open whether there 
compromise and due to the fact that many investigators do not like 
the term radiance factor, the use of the term reflectance factor, 
connected to the conical geometry, avoids the discrepancy between 
will be a 
the two terminology systems because it is used by both systems 
in the same way for the conical geometry. Therefore we recommend 
conditions ex- 
re- 
the term reflectance factor for all real measuring 
cept for the hemispherical measurement for which the term 
flectance is reserved, again in accordance with both terminology 
systems mentioned above. 
The characterization of the irradiation is still open. The usual 
radiation of 
suns's irra- 
case will be hemispherical irradiation because the 
sky and clouds cannot be neglected compared to the 
diation. Splitting of the reflection properties for different 
cones of the irradiation which would result in reflection data 
independent from the distribution of the irradiation, is mostly 
too elaborate to be carried out. But because this is possible, 
a distinction between these two cases should be made and it 
should be indicated whether it is a reflectance factor for hemis- 
pherical incidence or for conical incidence. The latter is the 
normal situation at laboratory measurements with only one source 
of irradiation.