To verify the depth range of our newly developed GPR receiver, we were delighted to cooperate with the Speleological Group Tartarus from Ostrov u Macochy town.

Measurements were carried out above the well known site of the Amateur cave and near Holstein cave. Eventually, several profiles were measured also in the unexplored parts of Ostrov u Macochy area.

Measurements were attended by geophysicist Dr. Pavel Kalenda, who carried out geophysical measurements using the vertical electrical sounding, gravity survey, shallow seismic and low frequencies method in this area for many years. His results helped specifying locations and depths of caves.

The measurement was performed with an antenna of 25 MHz frequency and a transmitter with a voltage of 10 kV. Antennas were towed by hand or behind cars with 6 m spacing and in up to 8 km/h speed. GPR receiver was equipped with a GPS with 2 meters accuracy, a data record was set for 5100 ns (est. depth up to 270 meters). Measuring step of 15 cm allowed us stacking 10 pulses.

Location of two profiles (20 m spacing) over Old Amateur Cave part

Location of two measured profiles

Confirmed cave and unknown cavitiesAlready confirmed cave is at 80 m depth, its centre on a position 340 m of the profile. Three distinct unknown cavities were detected at the depth of about 30 m (see black arrows) and another one at 75 m depth.

Other unknown cavities are on the left part of the radargram at a depth of about 70 m. At a depth of 25-40 meters there is a group of strong reflections from cavities. Wave speed 12 cm/ns corresponds to the table value for limestone and depth display corresponds to the actual depth of the cave at this point.