Ground measurements 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
  
  
From different sites of the test areas Iffeldorf and Kochel Moos ground 
measurements were taken concerning radiant temperature (with the Hei- 
mann KT 4 thermal IR radiometer, 8-14 u), temperature profile of the 
soil (at -0,05, -0,1, -0,2, -0,3 and -1,0 m with thermometer), air 
temperature and humidity at +0,2 and +1,5 m, profile of soil moisture 
and quality. One measuring campagne at least included 24 hours. 
Fig. 2 shows an example of the diurnal variation of the radiant tem- 
perature. For data evaluation the temperatures, read out each half 
hour in Sc, were averaged over three measurements. Those curves measured 
during the first phase in the program show the day time when to fly 
with a thermal scanner as it is indicated in fig. 2. 
The diurnal changes in the temperature profile of the soil were plotted 
as a function of depth and time. The isotherms in fig. 3 show a typi- 
cal thermal layering of the soil. At about -0,7 m there is a level 
of constant temperature. The value of temperature depends on soil 
characteristics and on season. At about -0,4 m there is another ther- 
mal level which is sometimes neutral, which in other cases is charac- 
terised by a positive gradient directed towards the surface and to- 
wards deeper layers. 
But the most important fact is that during night, from 8 p.m. to 6 a.m. 
a third level exists with a negative gradient towards the surface. 
This level was found everywhere, in southern, central and northern 
Germany, in vegetated and bare soils. That means at least at night 
times, moisture calculations which are based on thermal data, can 
only include the upper 0,1 m of the soil. 
On the other hand this thermal layering offers rather simple condi- 
tions to calculate soil moisture on the basis of heat flow calcula- 
tions as developed in the next chapter.