14
H.-I. Bolle
limestone with iron oxides. Under dry conditions with capillary water rise from Clevels calcium carbonate is brought up and calcification takes place with the
precipitated calcium carbonate in the B horizon below the root zone. A description
of the soil classification and soil properties is given by Bouwman (1990).
Fig. 3 gives a view at soils found in the Castilla-La Mancha area in Spain, where
the EFEDA (Bolle et al. 1993 and Bolle 1996) experiment took place. In near costal
plains and hilly areas (colline metallifere) of Tuscany often iron rich reddish and
sludge rich gray soils are found.
The constitution of the soils is an inseparable component of the water cycle over
Mediterranean land surfaces. It determines whether or not roots can reach some
water stored in deeper soil levels (Fig. 3) or have to rely upon rain water which they
catch with their shallow roots in the upper soil layer. Consequently, in the major
Mediterranean field experiments like EFEDA the structure of and water transfer
through the unsaturated zone of soils is of fundamental importance for the
investigation of water fluxes.
Soils as well as the vegetation have an important function for the energy budget
of the surface due to their reflectance of solar radiation and emittance of infrared
radiation. A few examples of the variety of observed spectral reflectances are given
in Fig. 4a-d which demonstrate the radiative characteristics of the surface.
In Fig. 4a the reflectance of some characteristic soils is reproduced which
demonstrate the dependence ofthe reflectance of both the chemical composition and
the surface structure. Two soils which often appear in close neighbourhood are the
red iron oxide containing soils and grey silty soils .. The "red" soil the reflectance of
which is shown here is of the Maremma near Venturina, Tuscany, Italy. It is
composed of 77% sand, 16% silt, 7 % clay, nearly no lime, its pH value in water is
7.1 and the conductivity 235 jJ.S/cm. The "grey" soil is of the area of Or ciano southeast of Livorno. Its composition is 33% sand, 65% silt, 2 % clay, it contains 18 %
lime components, its pH in water is 7.5 and its conductivity 2llO jJ.S/cm. These
very different compositions are responsible for the spectral slope of the reflectance.
The soil found close to Matera is covered with calcic stone pebbles which contribute
to the spectral features. The surface structure then determines the magnitude and the
angular dependency of the reflectance. The smoother the surface the higher is the
degree of reflection. Viewing against the direction of the sun results in lower
reflectances for rough surfaces and the view with the sun in the back in higher
values. For very smooth surfaces the reverse may be the case if there is a specular
component. In Fig. 4b the dependency of the reflectance on the soil moisture is
documented. Irrigation reduces the reflectance as long as the soil is not too wet and
one does not look into the sunglint. Due to evaporation and suction the moisture
dissipates from the surface and after a few hours the soil returns into the dry state
and the surface may now have a different, smoother, structure. The figure shows the
appearance of the water absorption bands at 1.4 and 1.8 jJ.m and that changes in the
reflectivity are measurable which happen within a few minutes.
If the surface is covered with gradually denser and biologically active vegetation
the reflectance in the visible part of the spectrum is reduced due to chlorophyll
absorption and the reflectance in the near infrared part of the spectrum is enhanced
H.-I. Bolle
limestone with iron oxides. Under dry conditions with capillary water rise from Clevels calcium carbonate is brought up and calcification takes place with the
precipitated calcium carbonate in the B horizon below the root zone. A description
of the soil classification and soil properties is given by Bouwman (1990).
Fig. 3 gives a view at soils found in the Castilla-La Mancha area in Spain, where
the EFEDA (Bolle et al. 1993 and Bolle 1996) experiment took place. In near costal
plains and hilly areas (colline metallifere) of Tuscany often iron rich reddish and
sludge rich gray soils are found.
The constitution of the soils is an inseparable component of the water cycle over
Mediterranean land surfaces. It determines whether or not roots can reach some
water stored in deeper soil levels (Fig. 3) or have to rely upon rain water which they
catch with their shallow roots in the upper soil layer. Consequently, in the major
Mediterranean field experiments like EFEDA the structure of and water transfer
through the unsaturated zone of soils is of fundamental importance for the
investigation of water fluxes.
Soils as well as the vegetation have an important function for the energy budget
of the surface due to their reflectance of solar radiation and emittance of infrared
radiation. A few examples of the variety of observed spectral reflectances are given
in Fig. 4a-d which demonstrate the radiative characteristics of the surface.
In Fig. 4a the reflectance of some characteristic soils is reproduced which
demonstrate the dependence ofthe reflectance of both the chemical composition and
the surface structure. Two soils which often appear in close neighbourhood are the
red iron oxide containing soils and grey silty soils .. The "red" soil the reflectance of
which is shown here is of the Maremma near Venturina, Tuscany, Italy. It is
composed of 77% sand, 16% silt, 7 % clay, nearly no lime, its pH value in water is
7.1 and the conductivity 235 jJ.S/cm. The "grey" soil is of the area of Or ciano southeast of Livorno. Its composition is 33% sand, 65% silt, 2 % clay, it contains 18 %
lime components, its pH in water is 7.5 and its conductivity 2llO jJ.S/cm. These
very different compositions are responsible for the spectral slope of the reflectance.
The soil found close to Matera is covered with calcic stone pebbles which contribute
to the spectral features. The surface structure then determines the magnitude and the
angular dependency of the reflectance. The smoother the surface the higher is the
degree of reflection. Viewing against the direction of the sun results in lower
reflectances for rough surfaces and the view with the sun in the back in higher
values. For very smooth surfaces the reverse may be the case if there is a specular
component. In Fig. 4b the dependency of the reflectance on the soil moisture is
documented. Irrigation reduces the reflectance as long as the soil is not too wet and
one does not look into the sunglint. Due to evaporation and suction the moisture
dissipates from the surface and after a few hours the soil returns into the dry state
and the surface may now have a different, smoother, structure. The figure shows the
appearance of the water absorption bands at 1.4 and 1.8 jJ.m and that changes in the
reflectivity are measurable which happen within a few minutes.
If the surface is covered with gradually denser and biologically active vegetation
the reflectance in the visible part of the spectrum is reduced due to chlorophyll
absorption and the reflectance in the near infrared part of the spectrum is enhanced