100 
investigate? eeparatiy the impact of the above mentioned parameters on 
the emissivity and furthermore to consider the influence on the surface 
roughness* 
In most loose sediments water is responsible for the electrical 
conductivity. The greater the electrical conductivity of the sediments 
is, the 1 ess the electromagnetic radiation is absorbed and emitted. 
Ideal conductors have no magnetic field inside and reflect all the 
incoming radiation. That means microwave radiation emitted from ground 
decreases. The higher the soil moisture is, the smaller the upper soil 
I a y e r i s w h e r e t h e m i e r o w a v e r a d i a t i o n c o m e s f r o m. 
The penetration depth for a given wavelength of 3 cm is about 0.8 cm to 
1 cm for dry sand <0.5 wt“4 water content). Moistening the sand to about 
5 wt“4 water content reduces the penetration depth less than 4 mm. At a 
water content of 20 wtX the emitting layer is only one or two 
millimeters. Therefore it may be concluded that microwave radiometers 
with \ -- 3cm contains black body radiation from the upper soil layer 
wi th a thickness of 0.5 cm to .1 cm 
For investigating the dependance of £ on moisture, surface roughness:, 
and substrate textures as series of field and laboratory experiments 
h a v e h e e n c a r r i e d o la t.. T h e r e s u 11 s o b t a i n e d h e r e b y h a v e b e e n th e 
f o1 Iowinq one s: 
a) Increasing substrate? moisture is causing decreasing emissivity 
va1ues of t he samp1e s.. 
The decrease is not linear in any case, however linear sections can 
be found. This is valid in particular for the water binding 
sediments. With sandy soils water dipoles are not attracted 
therefore £ decreases linearly with increasing water content 
(Fig.5). With sandy loam first the water dipoles are completely 
bonded between the layers after moistening. According to that £ only 
slowly decreases with 15 wt“4 water content. Only by exeeding a 
saturation value of the water binding between the clay mineral 
layers £ decreases more strongly with increasing moisture (Fig.6). 
2. 2 i 
!-• or 
b) The substrate influences mentioned under a) could also be detected 
during the field experiments (Table 2). Concerning the substrates 
differences between the decline of £ with increasing moisture have 
been detected. £ of dry loamy sand is greater than of dry sand. For