Estimation of the soil water content: Concerning soil moisture estimation, the physical principle of GPR is the same as of TDR measurement. The physical principle is based on the relationship between the EM wave velocity and the dielectric constant/electrical permittivity of soils. For example, the permittivity of dry soils varies between 3 and 6, whereas water has a value of 80. The permittivity of soils depends on the volumetric proportion of solid, fluid and gaseous components. Therefore, the dielectric constant correlates directly with the water content, but also is influenced by other parameters of the soil, like density or content of organic matter. The main difference is that TDR uses a guided EM wave, whereas the GPR technique is based on an unguided wave. Different techniques can be applied for soil moisture estimation by GPR. Generally, we can differentiate in the surface reflection, the reflection/diffraction, the ground wave and the transmission analysis method.
Exploring of hydro-geological structures: The spatial distribution of layers (e.g. ground water level) and structures within the soil can be identified by the analysis of the measured radargram.