Scale Transform Signal Processing for Reducing the Effect of Rain on SSTDR Signals

Spread spectrum time domain reflectometry (SSTDR) has proven to be effective in the detection and localization of intermittent faults on live electrical wiring. The location, shape, and magnitude of the peaks from the SSTDR signal give information about the location and type of wiring fault. To locate these faults, baseline subtraction is typically used. Unfortunately, varying weather conditions alter the SSTDR signal significantly and make baseline subtraction methods unreliable. Specifically, moisture from rain changes the relative permittivity of the cable and consequently leads to a change in the velocity of propagation (VOP) of the SSTDR signal. This change of VOP stretches the SSTDR signal and therefore shifts the peaks out of place, leading to inaccurate fault localization. Figure 1 (below) shows the described stretching effect rain has on SSTDR signals.