No signal underground.
I read the News article on the National Grid's inspection robot (PE January). You state that "Premtech will produce 3D maps of the trial sites and a GPS system for the robot".
The one thing that should be obvious is that the Navstar GPS signals do not traverse through steel pipes or soil. At best the GPS system can be used to initialise the robot's entry or exit position. After this the robot would be traversing using dead reckoning or deduced reckoning.
I would be very interested to know how Premtech intends using GPS in relation to the live data transmitted from the under-pressure robotic probe.
Telemetry can be transmitted using magnetic signals which entail tuned coils, basically a transmitter and a receiver coil. This is very much like vehicle door-locking systems using a key fob.
Magnetic waves are quite different to radio propagation and are not affected by rock and soil. Steel pipes however will reduce the magnetic field, limiting the distance that the telemetry can be received
David Caunter, Brisbane, Australia