Measuring the Electrical Properties of Coal Using Ground-Penetrating Radar

In situ estimates of permittivity and resistivity versus frequency are computed from the waveforms of ground-penetrating radar pulses using a spectral ratio technique. Pulse transmission data traces were collected through coal pillars in three mines, using synthetic pulse radar equipment operating in the 20-160 MHz frequency interval. Vertically polarized transmissions were run in all three mines, and horizontal transmissions in one mine. The resulting permittivity values decrease slightly with increasing frequency, and resistivity decreases significantly and approximately linearly with increasing frequency above 50 MHz. Horizontal polarization exhibits higher permittivity and lower resistivity than vertical polarization.