Spikes were found in the long term data trend. It is assumed that these spikes correspond to the movement near the test site. For example, there is a railway line that passes nearby and throughout the day trains use the line. To test this theory a measurement was made while a train was passing. The measurement started while the train was near the office and finished after it could no longer be heard. The entire measurement took less than two minutes so two minute intervals should not be used to analyse the data as was done in Section 8.2.5. Instead intervals of 100 samples were used corresponding to approximately 1.5 seconds. Figure G.1 shows the standard deviation in Y of one of the marker’s centroids.
s expected, the standard deviation is high while the train is passing and drops away as the train leaves. This was expected as vibrations can be felt at the test site while trains are moving nearby.