More important, however, is the fact, that the curves for moisture
values greater than 30 Z take a vertical course. That means, that higher
water contents cannot be determined by experimentally gathered tem-
perature gradients but they have to be calculated on the basis of quan-
titative knowledge of all parameters which influence the physical pro-
cess of heating the soil. But even the temperature gradients of samples
with lower water contents vary considerably.
Further limits of the method are given by the definition of thermal
inertia. Moisture calculations can only be carried out if specific heat
capacity and heat conductivity are known. Heat conductivity includes
the fraction of air in the soil; but air contents depends on water con-
tents, which is unknown.
Thermal inertia and soil mapping
Although thermal inertia does not seem to be useful for calculations
of soil moisture, it can be taken as complex indicator for soil pro-
perties. Therefore a method had to be found which allows to map soil
differences in spite of an intensive land use pattern which hides
borders between soil units.
Basis for this research were thermal scanner data taken at 1000 m above
ground before sunrise and before noon. The data were calibrated by the
black body temperatures of the scanner and intersected in intervals of
1,25 °C (night time) and 2,5 °C (day time).
First attempts were made in the Kochel Moos area, where the following
combinations of soil and vegetation were distinguished:
- drained areas separated in fields with mown grass and in those
with not mown grass,
- poor drained areas and marginal parts between drained and undrained
areas,
swampy areas which were covered by much dead rush and reedgrass.