Ground Penetrating Radar Attenuation Expressions in Shallow Groundwater Research

Abstract

The electromagnetic-wave attenuation coefficient determines the overall resolution and effective penetration depth of ground penetrating radar (GPR) surveys. Despite this relevance to the design of proper GPR surveys, the attenuation expressions are rarely used in the applied shallow groundwater research (SGR) literature. This work examines the status of the attenuation expressions in SGR. For this, 73 GPR case studies (in 47 papers), including some information concerning the attenuation variables and parameters, were selected to build a database. From these, 18 cases (in 10 papers) provided attenuation expressions and only 11 cases (in 4 papers) used those expressions. Two types of expressions were identified, physically based global ones that try to solve a broad (but not complete) range of environmental and field technical conditions, and non-global ones adapted for specific geological environments and resolution needed. The database analysis showed that both global and non-global expressions were used exclusively in low-loss media to report an attenuation range of 0.1–21.5 dB m −1 by using common antenna frequencies in the 25–900 MHz range. The range of the attenuation expressions validity in SGR is biased because no surveys in variable-loss heterogeneous media and wider antenna frequency intervals could be compiled. The attenuation database generated seeks to improve the design of GPR surveys in SGR.

A K-Nearest Neighbors Algorithm in Python for Visualizing the 3D Stratigraphic Architecture of the Llobregat River Delta in NE Spain

“…In this and other cases, the accuracy of predictions depends on available data density, as expected. In other sparse data areas, the readers can use widely-known empirical relationships to indirectly infer granulometry from physical parameters deduced from hydraulic tests such as pumping tests, geotechnical tests such as Lefranc, Digital Image Analysis of ground textures, or pore-water findings from geophysical surveys such as Electrical Resistivity Tomography and Ground Penetrating Radar techniques [57][58][59][60][61][62][63]. In these cases, a representative enough granulometry dataset from each lithological class is needed to ensure the statistical representativeness of the measured vs. deduced data pairs experimental relationships.…”

Combining of MASW and GPR Imaging and Hydrogeological Surveys for the Groundwater Resource Evaluation in a Coastal Urban Area in Southern Spain

“…The propagation velocity of electromagnetic waves (VE) [L T −1 ] and their amplitudes through the subsurface depends on the electrical and magnetic properties of geological materials and the adopted antenna frequency [55][56][57][58]. Penetration depth of the electromagnetic signal decreases as the clay content and salinity of the media and the antenna center frequency increase [33,55,[58][59][60][61].…”

“…The GPR technique was chosen to disambiguate these structures having similar VS values, as well as to identify key hydrogeological features, such as piezometric level, capillary fringe, and seawater-freshwater interface (Figure 5). MASW provides higher exploration depths than GPR, but less detailed resolution, whereas GPR is highly responsive to detailed subsurface electrical and magnetic changes related to natural and human-induced geological and hydrological heterogeneities [33,55,[58][59][60].…”