Easy HVSR > Graphics > Directionality map

Directionality map

This map is present in the "Selection" and "Spectral analysis" windows. It shows the trend of the H/V spectral ratio with the variation of the angle formed by the direction of recording and the reference system. In fact, in the calculation is recomposed the spectrum in one direction assuming to vary the two reference systems (that of the instrument and that of the calculation) through a rotation around the vertical axis, from 0 to 180 °.

In practice, on the abscissa axis are shown the degrees of this rotation, on the ordinate axis the frequencies and the color map represents the spectral width of the H/V ratio. Then each point is the spectral width at a given frequency for a given angle of inclination of the horizontal direction of the spectrum compared to the reference system.

This map is used to demonstrate the isotropy of the recording, or the absence of a source that has a preferential direction and that therefore would vitiate the validity of the registration. In fact would violate the assumptions underlying the theory that the sources are evenly distributed.