termines the diurnal evolution of the atmospheric boundary layer (Callies et al., 1998) . Currently, there is a needWe present a comprehensive review of methods to measure soil to establish and quantify the contribution of soil water water content with ground penetrating radar (GPR). We distinguish content-regulated land-atmosphere coupling to regional

We present a comprehensive review of methods to measure soil water content with ground penetrating radar (GPR). We distinguish four methodologies: soil water content determined from reflected wave velocity, soil water content determined from ground wave velocity, soil water content determined from transmitted wave velocity between boreholes, and soil water content determined from the surface reflection coefficient. For each of these four methodologies, we discuss the basic principles, illustrate the quality of the data with field examples, discuss the possibilities and limitations, and identify areas where future research is required. We hope that this review will further stimulate the community to consider ground penetrating radar as one of the possible tools to measure soil water content.

Seven hundred seventy liters of a dense nonaqueous phase liquid (DNAPL), tetrachloroethylene (PCE), were released into an isolated volume of a completely saturated natural sandy aquifer. The release was monitored over a period of 984 hours with a variety of geophysical methods including ground penetrating radar, time domain reflectometry, in situ resistivity, and a neutron soil moisture probe. The PCE formed a pool on a low permeability layer at approximately 1 m depth and spread over an area exceeding 32 m2. In its course of downward migration, the PCE subsequently formed eight smaller pools. At the end of the experiment an estimated 41 percent of the total PCE volume remained trapped in the upper pool. The PCE mass and its spatial moments were calculated from radar reflection amplitudes. Between 48 and 100 percent of the PCE mass was accounted for by radar measurements. The center of mass moved a total of 0.5 m south southeast and 1.3 m downward. Spatial variances showed that the greatest lateral spreading occurred in the east‐west direction. The results demonstrate that natural heterogeneities, even in a relatively homogeneous aquifer, can cause DNAPLs to spread laterally over large areas in the subsurface. This experiment also demonstrated that while the ability of geophysics to uniquely measure the presence of DNAPL is limited, certain techniques are well‐suited to monitoring changes in DNAPL saturation.

Abstract:The spatial variability of soil water content can be measured with the ground wave velocity of ground-penetrating radar (GPR) using short antenna offsets, but picking the correct ground wave arrival time is rather difficult. In applying the GPR ground wave method to soil water content estimation it is also important to know the effective sampling depth of the method. Uniform drainage experiments were conducted with 100 and 450 MHz GPR antennas using 1Ð0 and 2Ð0 m fixed antenna separations on a sandy loam soil to investigate time zero picking methodologies and to estimate the sampling depth of the GPR method. The GPR water content data were compared with time-domain reflectometry (TDR)-measured data using six vertical TDR probes of different lengths. Time zero was calculated from an air calibration at a 2Ð0 m antenna separation and from wide-angle reflection and refraction data, and a difference was found between the two time-zero calibration methods. A method was analysed to determine the arrival time of the leading edge of the direct ground wavelet using the arrival time of the peak amplitude, since the arrival time of the leading edge of the ground wave can be difficult to pick. Regression analysis showed that the GPR (100 MHz) measured water content was not different from the water content measured with TDR at 0-0Ð1 m depth, implying that this may be a reasonable estimate of the GPR ground wave method's sampling depth. A similar analysis based on the differences between the 0-0Ð2 m TDR and the GPR shows that the effective sampling depth of the direct ground wave of the 450 MHz data is less than the sampling depth of the 100 MHz data.

The identification of the physical nature of an object\ud or target causing a ground-penetrating radar (GPR) anomaly, as\ud well as the estimation of a target’s dimensions and geometry, is\ud rather challenging. To improve target identification, basic studies\ud are still required, and they can be addressed primarily using a\ud laboratory- or field-based physical model. The field model (test\ud site) is usually expensive and difficult to build, but it provides\ud data for controlled target properties and geometry from a natural\ud environment that are essential for testing processing techniques.\ud In this paper, we present the results from a field experiment where\ud GPR data were collected on plastic and metallic pipes. The main\ud objective is the comparison of the classical migration technique\ud with a microwave tomography approach for reconstructing the\ud geometrical target properties. The use of the microwave tomography\ud approach will allow us to obtain more focused and stable\ud images of the buried objects compared to the ones obtained using\ud classical migration techniques