A method and apparatus includes detecting lightning induced electromagnetic pulses and determining a physical property of an underground structure based on the lightning induced electromagnetic pulses. In some embodiments, an apparatus includes an antenna, a low noise amplifier, a processor, cable, and a transmitter. The antenna includes three substantively perpendicular loops of electrical conductors. The processor is configured to condition the amplified signal. The cable is about 100 meters in length and connects the low noise amplifier to the processor. The transmitter is configured to send conditioned data to a data aggregation system.