An earlier system was SLIFER (Shorted Location Indicator by Frequency of Electrical Resonance). It used the same idea of a coaxial cable progressively shorted b

An earlier system was SLIFER (Shorted Location Indicator by Frequency of Electrical Resonance). It used the same idea of a coaxial cable progressively shorted by the blast wave. However, instead of using reflectometry, it used a resonant Colpitts oscillator whose frequency was 1/4 wavelength. So as the cable was crushed, the frequency increased. Plotting the frequency vs time showed the progression of the blast wave. The oscillator itself was a small circuit board in the blast hole, while data was recorded in a separate trailer. To quote the paper: "In the event the recording facility must be located near surface zero, shock mitigation may be required to assure survival of equipment." The paper includes PCB layouts in case you want to make your own SLIFER system :-) Thanks to kps for the SLIFER link: https://www.osti.gov/biblio/7352892 https://www.osti.gov/biblio/7352892