Underground radiolocation

How does it work?

Underground positioning via magnetic beacon (or radiolocation) consists of the positioning on ground surface of a cavity located underground, as deep as 300 meters.

In order to exactly localize the cavity, the beacon emits an electromagnetic wave. Its magnetic field is then sensed by a sensor/receiver. The place where the magnetic field equals zero corresponds to the exact vertical line produced by the transmitter.

Radiolocation principle

Such data is most commonly used to position underground rivers and siphons, as well as to determine the position of caves in order to manage karstic hazards.

This technique is both precise and easy to deploy – it is most useful for underground network that span over many kilometers. In those situations, realizing a theodolite topography would be rather time consuming, or might even turn out to be impossible depending on difficult access conditions like narrow or muddy corridors, underwater or drenched passes…

Compared to traditional topography techniques used by speleologists, this technology allows for much more precise data.
Whereas in the past one could expect from 5 to 10% typical error – ie a potential 50 to 100 m X-Y error for a 1km long gallery - now this error has been improved to reach 1% only.

Therefore, if we consider a 200m deep cavity, the error margin is now reduced to 2m in X-Y. It also allows calculating the depth at which the cave is located, with a precision under 10%.

Data gathering errors can come from the beacon verticality, the paramagnetic nature of some rocks or sediments, which may interfere with the electromagnetic field.

Positioning a cave with radiolocation
This shows both the previous topography (pale colors) and the new, repositioned with reference to the ground surface. It is clear why the previous drilling, based on the speleological topography, was a failure: it was realized 40m from the siphon. Note: data has been slightly modified to comply with confidentiality.

Our beacons

Given the very specific niche applications for this type of technology, there is no beacon readily available on markets.
NOT Engineers has therefore developed two electromagnetic beacons that allow for underground positioning:

6W beacon:
- 50m range
- used for low depth caves
50W beacon:
- precise up to 300m deep
- used to locate deep caves

These beacons are fully waterproof, which allows for use in underwater cavities. They can function several days in a row without recharging and have been tested in extreme conditions: in a mountainous environment, under 300m of rocks, and at a depth of 40m in 2°C water.

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