From their FAQ, they pick up RF pulses, tag it with a GPS timestamp, and correlate on a central server.
"A lightning is a pulse not comparable to a broadcast signal on a single frequency. Such a pulse can be described best as a interference of several frequencies. Therefore a ferrite rod for lightning detection has to be a wide-band antenna."
"A lightning is a pulse not comparable to a broadcast signal on a single frequency. Such a pulse can be described best as a interference of several frequencies. Therefore a ferrite rod for lightning detection has to be a wide-band antenna."