[kaybe]

It should be possible to hack together a basic TDR device, especially if you can calibrate it.

Then one needs a/two metal piece of defined length, and a high-frequency oscilloscope, that can also give a pulsed signal (ideally of high frequency).

The biggest issue I see is that you'd need something like at least 0.5 GHz resolution in the oscilloscope with a metal piece of 25cm (quick mental math and some guesses, don't hold me to it). Probably better to have at least 2 GHz. I don't think computers and software alone is up to it after a quick search. Maybe one can increase the travel time in the probe (metal stick) somehow to lower the needed resolution, but not by orders of magnitude.

https://electronics.stackexchange.com/questions/268333/ghz-c...