Directionality map

This map is present in the configurations relating to the Tabs named Selection and Spectral analysis. It shows how the H/V spectral ratio varies with the angle formed between the recording direction and the reference system. In the computation the spectrum is recomposed along one direction, assuming that the two reference systems (that of the instrument and that of the computation) are rotated with respect to each other about the vertical axis, from 0 to 180°.

In practice the abscissa axis carries the degrees of this rotation, the ordinate axis the frequencies, and the colour map represents the spectral amplitude of the H/V ratio. Each point therefore represents the spectral amplitude at a given frequency for a given inclination angle of the horizontal spectrum direction with respect to the reference system.

This map serves to demonstrate the isotropy of the recording, that is the absence of a source with a preferential direction which would invalidate the recording. Such a source would violate the assumption, underlying the theory, that the sources are uniformly distributed.

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