This chapter discusses the concept of soil dielectrics, available techniques for the determination of soil dielectric permittivity and soil moisture content, and the associated theoretical background for a better understanding of the measured soil dielectric property and the moisture content.
Frequency Domain Analysis (FDA), as an approach, has been developed for the measurement of soil dielectric constants.
Because soil dielectric constant receives combination influence of soil properties, statistical methods were used to analyze the influence of soil bulk density on electromagnetic wave velocity.
A full-wave GPR model, a soil dielectric mixing model and the Debye equation were combined to directly estimate soil moisture from GPR measurements.
While soil dielectric constant strongly depends on soil water content, the growing of soil bulk density usually reduces free water content, increases bound water content and finally influences GPR signals.
The package consists of a soil dielectric spectroscopy probe (SDSP), a ground penetrating radar (GPR) and a time domain electromagnetic measurement (TDEM) system that, using different methods, estimate the electromagnetic properties of the shallow subsurface at different depths (0 100 m).
Soil moisture content was monitored indirectly approximately monthly for half a year using a variety of methods with different measurement scales including: 2D electrical resistivity (ER) imaging and surface and vertical profiles using probes which measure soil dielectric properties.
These methods need some parameters such as scanning velocity, soil dielectric, soil conductivity, etc.
A more realistic frozen-soil model requires a soil dielectric permittivity dependence with depth, and a relationship between the soil dielectric permittivity and soil moisture, as well as soil material composition [22, 28, 29].
Since the soil dielectric constant and reflectivity depend on soil moisture, the variation in the reflected GNSS signal power, or SNR, indicates changes in soil moisture [65].
