Environmental Engineering Reference
In-Depth Information
each moisture level) the TDR measurements could be carried out. To avoid varia-
tions in moisture profile along the probe, due to gravity effects, the cylindrical holder
was kept horizontal during all measurements. The sample temperature was kept at
27
1
◦
C
during all the experimental session.
For each moisture level, two TDR waveforms were acquired: one with a very long
acquisition window and the other with a shorter one. The former was used for the
evaluation of
±
0
through the Castiglione-Shouse method [8]; whereas the latter was
used both for the estimation of the dielectric constant through the traditional TDR
method [10] and for obtaining
S
11
,
MEAS
σ
to be used in the subsequent minimiza-
tion procedure. For the sake of example, Fig. 5.7 shows a typical TDR waveform
(corresponding to the dry sand sample), acquired with a short acquisition window.
Finally, to perform the aforementioned TSC, the TDR waveforms corresponding
to three short-circuit conditions obtained at different sections of the probe were
acquired. The short-circuit conditions were achieved by short-circuiting the probe
rods (at the desired section) by means of a perforated copper slab with a 'guillotine
configuration' (see Fig. 5.8). All the TDR waveforms measured at section B were
preliminarily FFT-processed and corrected by means of (5.19), thus obtaining the
S
11
,
MEAS
(
(
f
)
f
)
at section A to be used in the minimization procedure.
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Fig. 5.7
Typical TDR wave-
form (for the dry sand sam-
ple) acquired with a short
acquisition window [48]
-0.2
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
apparent distance (m)
Fig. 5.8
Schematization of
the perforated slab used for
obtaining the short-circuit
condition [48]
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