Why using an unshielded antenna inside closed space is a bad idea

Any unshielded antenna, transmits the signal both into the ground (desired direction) and into the surrounding air.

If there are objects surrounding the antenna above the ground, the signal will reflect from them.

These air reflections are strong (no attenuation in the air) compared to the reflections coming from the ground (soil attenuation).

Inside a tunnel/building/urban environment, the amount of air reflections is huge and can completely mask the reflections coming from the ground.

As an example of a "minor" air reflection that could be wrongly interpreted or mask an underground response, please see the movie on our youtube channel:

GPR and Soil conductivity  (at 2:00 mark)

That is why using unshielded antennas like our Gekko series or similar solutions from other manufacturers are not the best choice for this kind of a surveys.