Study Area

The geophysical survey focused on an olive grove plot located in the Kavros area, where a new hotel unit is planned to be constructed. The purpose of the survey was the horizontal mapping of subsurface physical properties using the Ground Penetrating Radar (GPR) method, to a depth of approximately two meters from ground surface, aiming at detecting buried structures potentially related to anthropogenic remains.

The electrical resistivity tomography method was also used to reconstruct the vertical stratigraphy of the subsurface down to a depth of approximately 10 meters.

The area investigated with ground penetrating radar within the Kavros plot covers 3,740 square meters.

Ground Penetrating Radar Method

Ground Penetrating Radar (GPR) is an electromagnetic geophysical technique applied in mapping soil and rock layers as well as in detecting underground structures, based on differences in the electrical properties of materials.

The method operates by transmitting high-frequency electromagnetic radiation into the ground and recording the reflected waves. Reflections occur at interfaces where materials possess different electrical properties.

A short-duration high-frequency electromagnetic pulse is transmitted into the ground. The signal propagates through subsurface materials and its path depends on the surrounding material properties. Part of the signal energy is reflected at boundaries between materials with differing properties and is recorded by a receiver located at ground surface, while the remaining energy continues deeper underground.

The time interval between emitted and received pulses depends on the propagation velocity along the traveled path. When the wave velocity is known, reflector depth can be calculated. In most geological materials, electrical conductivity and dielectric permittivity mainly affect signal propagation. Signal absorption additionally depends on antenna frequency, conductivity and dielectric constant. Greater penetration depth is achieved using lower frequencies, while higher frequencies provide better resolution but shallower penetration.

The NOGGIN PLUS GPR system equipped with 250 MHz antennas was used for mapping the plot.

The method can be applied in various cases such as:

Mapping bedrock depth,
Determining layer thickness,
Detecting groundwater levels,
Locating natural and artificial cavities,
Identifying lithological changes,
Detecting fractures,
Archaeological investigations for buried remains.

Data acquisition was conducted in grid patterns with parallel survey lines spaced at 0.5 m, while sampling along lines was performed every 0.05 m. Areas containing obstacles such as trees could not be surveyed due to instrument access limitations.

Data collection was carried out using the Sensors & Software NOGGIN Plus system with a central antenna frequency of 250 MHz. Maximum signal penetration reached approximately 2–2.5 meters, depending on subsurface electrical properties.

Interpretation of Results

Representative horizontal slices were selected for interpretation. A color scale was applied where:

Red colors indicate strong reflectivity and strong variation in subsurface electrical properties.
Blue colors indicate low or zero reflectivity associated with homogeneous materials or strong signal attenuation.

GPR slices were georeferenced using ArcGIS 10.6 in the Greek coordinate system (EGSA ’87). A georeferenced Google Earth satellite image (2013) was used as a background layer for overlaying results.

At shallow depths (10–20 cm), point anomalies of high reflectivity were observed, corresponding to localized variations in soil electrical properties caused by deposition of more resistive soil material. A diagonal linear anomaly in the southwest portion of the plot is associated with coarse material deposition.

At depths greater than 40 cm, circular high-reflectivity zones approximately one meter in diameter appear in regular patterns along two perpendicular directions. Overlaying GPR slices with satellite imagery confirms that these anomalies correspond to the positions of olive trees within the plot. The root systems and dense planting pattern are clearly reflected as zones of strong reflectivity.

Final GPR maps effectively depict olive tree positions due to strong electrical property contrast between root systems and surrounding soil. This contrast significantly reduced the method’s resolving power, preventing clear detection of possible buried architectural remains.