Stationarity map

This map is present in the configurations relating to the Tabs named Selection and Spectral analysis. It shows the H/V spectral ratio of each individual window. It is organised so that the abscissa axis carries the starting time instants of each window, while the ordinate axis carries the analysed frequencies. The colour map therefore represents, at each point, the spectral amplitude at a given frequency of the H/V spectral ratio associated with a given selected window, according to a colour coding.

The usefulness of this chart lies in the possibility of verifying that the H/V spectral ratio of all the windows behaves homogeneously. In plain terms, this map should show spectral amplitudes that are constant in time, and therefore a concentration of the spectral amplitudes along the same frequencies.

With the help of this chart it is possible to decide to discard windows whose spectral content shows anomalies with respect to the average trend, that is, significant content even at frequencies where the other spectral ratios show no appreciable values. The presence of these windows only widens the confidence interval of the final average H/V curve, and damages the reliability of the processing. This usually happens at low frequencies, below 1 Hz, where ambient noise is of natural origin and its source is very distant compared with anthropic sources (much closer), which can easily disturb the content of low frequency natural sources.

To select the spectrum relating to one of the windows, simply click on it: the corresponding window will automatically be highlighted both in the trace charts and in the window table (both the one in the Selection Tab and the one in the spectral analysis Tab).

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