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measurements have to be required. 
Thermal inertia and soil moisture 
Basics 
Two of the most important heat properties of soils, heat conductivity 
À and specific heat capacity Co make part of thermal inertia P: 
(3) P= Y (cs x mo) x À 
For the calculation of P temperature differences have to be measured 
Concerning radiant temperature these differences are related to two 
measuring times in one level (the surface) only. This possibility seemed 
to be the most obvious way for the experiments on soil moisture cal- 
culation [2], [3]. Different thermal inertia caused by water contents 
influences the diurnal variation of surface temperatures in a way [4] 
that: 
material of high thermal inertia cools and warms more slowly than 
that of low P; 
- material of low P cools lower and warms higher than that of high P; 
- there are best possibilities to detect materials of different 
thermal inertia shortly after high noon and during night (shortly 
after sunset - shortly before sunrise). 
Evaluation of radiometric data 
Measurements of the diurnal variation of surface temperatures taken 
since 1974, have shown that the above mentioned ideal results are 
obtained seldom because of the influence of atmosphere and vegetation. 
The temperature gradient (c/hr) of the cooling phase, however, allows 
the separation of areas with different moisture contents. 
Fig. 8 points out the limits of this method. The gradients of the 
heating phase vary considerably more than those of the cooling phase.