Agriculture Reference
In-Depth Information
GPS antenna
electrodes
for supply
of current
electrodes for sensing
of voltage
1
2
3
4
5
depth 1
soil surface
depth 2
depth 3
depth 4
depth 5
0.5 m
top view
equatorial dipole-dipole array
driving direction
adjustable dipole spacing
Fig. 5.7
Sensing electrical conductivity in a contact mode by the Geophylus electricus via rolling
electrodes that are spaced in the direction of travel (From Lueck et al.
2009
, altered)
A response to this problem for layered soils is successive or simultaneous sensing
along response curves that have different
gradients with depth
. It has been shown
(Mertens et al.
2008
; Saey et al.
2009
; Sudduth et al.
2010
) that special software and
differences existing in the response curves of the present sensing implements allow
for a rough delineation of soil layers. In case the soil within a field consists of only
two layers with distinct differences in electrical conductivities, this vertical horizon
sensing can be quite successful.
A special data processing technique has been developed - called
inversion of
electrical conductivity
measurements - that aims at mapping special layers or hori-
zons. This technique is not simple since the sensed volumes of different response
curves (Fig.
5.6
) overlap and because it must be prevented that different combina-
tions of layers with their respective conductivities generate the same final result
(Gebbers et al.
2007
; Sudduth et al.
2013
). It is obvious that the precision in the
detection of soil layers can be enhanced if signals from more than two response
curves within the respective soil depth can be obtained.
The “
Geophilus electricus
” - a development of the University of Potsdam and
the Technical University of Berlin - delivers signals along five response curves or
even more simultaneously on-the-go (Lueck et al.
2009
; Lueck and Ruehlmann
2013
; Radic
2008
). The implement is based on rolling electrodes, so it operates in
the contact mode as the instrument in Fig.
5.3
. The rolling electrodes are spiked at
the circumference. However, the current electrodes on the one hand and the voltage
electrodes on the other hand are not arranged on one axis perpendicular to the direc-
tion of travel (Fig.
5.3
), but instead they run in pairs that are separated in the direc-
tion of travel (Fig.
5.7
). Five voltage electrode pairs - spaced at successive distances
