OCTAVE Dispcurve.m - SASW analysis of frequency domain recorded spectra
Dispcurve no prompts, hard wired input file:
20mSourceOffset.mat Matlab file (91x21) 91 frequencies, 21 stations
SASW is Spectral Analysis of Surface Waves. Following description of data is from Dr. Brady Cox <brcox@utexas.edu>. Data were acquired in a benchmark project. Investigator analysis papers published by ASCE ISBN: 9780784413296 (GeoCongress 2014).
Acquisition Parameters Minimum sampling rate of 25.6 samples per second with time windows continuously adjusted by the analyzers for each frequency increment. Data provided in frequency domain only (i.e., linear spectrum from 10 â 1 Hz for each receiver). See included file, "UTexas1VibroseisData.txt", for additional details on data.
From within an octave session, type Dispcurve. This program, Dispcurve.m, shows how to compute a dispersion curve from pairs of receivers which recorded constant frequency tests (91 frequencies, 21 receivers). The 21 receiver stations were located at increasing distance from the source. Pairs of receivers are taken 2 at a time in this code (stations 2+1, 3+2, 4+3, etc.). At each frequency, phase difference between adjacent stations is computed, unwrapped, and then used to compute a time shift between stations, "dt". The ratio of the station separations to time shift gives phase velocity for that frequency. Consistent phase velocity results for many pairs supports a valid result. Scatter in phase velocity supports an interpretation of insufficient radiation recorded at that frequency.
The differences between saswv.m and Dispcurve.m are in the source and type of data. Example saswv.m code works on data which are cross-spectra. In Dispcurve.m, the sample data are frequency domain recordings at each station, and from those data, cross-spectra are computed. A unique opportunity here resides in the opportunity to compare many pairs of stations for consistency in result. So while the frequencies swept varied from 10 to 1 Hz, useful data appear to be above 5 Hz.
Figure 1 Phase velocity frequency dispersion estimates and coherence measurments.
20mSourceOffset.mat data file in Matlab format.
OCTAVE: saswv.m(7) SASW.m(7)
No known bugs.
Copyright © 2017 by Paul Michaels
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
P. Michaels, PE. <pm@cgiss.boisestate.edu>