Geopsy: Structure spectrum

Structure spectrum is an advanced signal processing tool aiming at computing the Transfer function of a system, i.e. to deconvolve signals, mainly civil engineering structures.

Background

, i.e. the solution of the homogeneous equation

ATTENTION no Transfer function, good in frequency, not in amplitude (Konno et Omachi)

Pre-Processing

Before starting the Structure spectrum toolbox, the signals should be rearranged by pairs. In the pre-processing toolbox (see below), check-boxes allow to discard Z, N or E components, therefore simplifying this procedure. Moreover, in case of odd number of signals, the last one is removed. The toolbox will compute the Transfer function between the first and the second signal, i.e. the spectral ratio of the second over the first signal. In a building, the bottom recording should therefore be placed first and the top recording second.

When starting the Structure spectrum toolbox using the Menu Tools or using the Toolbar, a pop-up menu allows several pre-processing:

• Excludes components. 3 check boxes allow to discard Vertical and/or North and/or East components. This is to help the rearrangement of signals.
• Third signal operation. A third signal is added to each pair of signals that will be used in the deconvolution (see Deconvolution). Two possibilities are offered:
  • Difference computes the difference signal 1 minus signal 2 for each pair of signals. For bottom and top recordings in a building, this corresponds to the relative motion of the structure (see Background)
  • Average computes the average of each pair of signals. It seems to be an obsolete option.

computes the transfer functions between signals in the active signal viewer.