Train Signal 

The railway line is only 130 away from the Raspberry Shake.

Regular trains have not run on this line since 14-Nov-2016 when the Kaikoura EQ destroyed the line to the north. The line has been repaired and the trains are slowly coming back, but regular service has not resumed yet.

Here is the raw signal from a train passing. The signal slowly builds in strength, then dies away.

This plot shows the continuous wavelet spectrum of the central 20 s of the signal. It is a way of showing how the energy is distributed with the period of the oscillations (vertical axis) and time (horizontal axis). The contours vary from brown (high energy) to blue (low energy).

The period of the main oscillations is just under 0.14 s, or 7.1 Hz, which corresponds to 430 revs per minute (rpm). For wheels of 0.5 m in diameter, this would correspond to a speed of 40 kph, which seems about right. The two blobs that occur first with longer period (about 0.17 s) could be the locomotive which has larger wheels. In fact, they would be larger by 0.17/0.14 = 1.2 times, which seems reasonable.

The signals are a series of pulses about 1 s apart. This probably reflects the joints in the rails.