Environmental Engineering Reference
In-Depth Information
Chapter 5
Qualitative Characterization of Granular
Materials and Moisture Measurements
'There are two possible outcomes: if the result confirms the
hypothesis, then you've made a measurement. If the result is
contrary to the hypothesis, then you've made a discovery.'
Enrico Fermi
Abstract.
This chapter focuses on broadband microwave reflectometry (BMR) ap-
plications for monitoring water content (
σ
0
)of
granular materials, with particular emphasis on applications for soil measurements.
First, a TDR-based method for inferring
θ
) and static electrical conductivity (
from measurements of the apparent di-
electric permittivity is presented. This approach, which relies on the individuation
of so-called
calibration curves
, is discussed in detail and the related metrological as-
sessment is provided. Successively, a more accurate method that takes into account
the frequency-dependence of the dielectric permittivity of the moistened granular
material (considering the permittivity of each single constituent) is presented. This
application is also used as test-case for validating an innovative calibration proce-
dure that is particualrly useful when the traditional short-open-load (SOL) calibra-
tion cannot be performed. Furthermore, the adoption of antennas in place of the
traditional probes is discussed (thus assessing the possibility of guaranteeing a non-
invasive approach). Finally, two innovative strategies for enhancing and simplifying
TDR-based measurements of static electrical conductivity
θ
σ
0
(typically used in soil
science) are presented.
5.1
Introduction
Measuring water content of granular materials represents one of the major practi-
cal applications of broadband microwave reflectometry (BMR), especially for soil
moisture measurements.
Indeed, reflectometric techniques have become increasingly attractive solutions
for soil moisture sensing, with applications that focus on environmental monitoring
purposes [60] and agricultural water management [18, 51]. In fact, mostly thanks to
the versatility of the technique, a wide variety of monitoring tasks can be effectively
performed through BMR [14].
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