Menu Entry Beam
This command takes the values of slowness and back-azimuth from the analysis parameter box and computes delay times for each trace on display so that signals of a plane wavefront of this orientation (given by slowness and azimuth) are aligned in time. The delays are applied to the traces and a sum trace is added to the display. The result of this operation is good, that means the scatter in time of the aligned phase is small between the traces and the sum traces shows an enhanced signal to noise ratio, if the following conditions are met:
- The slowness and azimuth values are properly determined.
- The assumption of a plane wave is applicable
- The dominant frequencies of the signal still allow coherency
This command is organized as a toggle function. Selecting once performs delay and sum of the traces, selecting a second time restores the original positions of the traces and deletes the beam trace. With this operation the results of slowness determination (by Plane Wave or by FK) may be checked or an amplitude/magnitude measurement on the beam trace may be performed.
This command needs the location of your recording stations in the station information file (see How to put station information into SH/SHM). Required entries are lat and lon, recommended is xrel, yrel and array. If the relative locations are not found in the file, SHM computes it from the latitude and longitude. The algorithm used is very simple might not be accurate enough.
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