Extracted from:
 UTexas1 Surface Wave Dataset: Information and Instructions 
Author: Dr. Brady Cox
<brcox@utexas.edu>

Data File:  20mSourceOffset.mat

(b) Active-source (vibroseis) linear array data:
Data Format – Linear spectra in both Ascii (.txt) and Matlab (.mat) format

Receivers – 21 vertical 1.0-Hz geophones (Mark Products L-4C) gravity coupled to 
an aluminum leveling base that was in turn coupled to the ground surface (grass) 
with three 7.6-cm spikes. All sensors were spaced at an equal interval of 10 m 
(total array length of 200 m).

Source – Large triaxial vibroseis truck (TRex; 
http://nees.utexas.edu/Equipment-T-Rex.shtml). The truck was positioned at three 
different “shot” locations relative to the first geophone in the array; namely, 
source-offset distances of -20-m, -40-m and -80-m. The source was not “reversed” 
at the opposite end of the array. For each source-offset location, the vibroseis 
was stepped from 10 Hz to 1 Hz in 0.1 Hz increments (91 points total). At least 
50 cycles of data for each frequency were averaged in the frequency domain. Each 
stepped sine test lasted approximately 25 minutes.

Acquisition System – Two 16-channel Mobilyzer dynamic signal analyzers 
manufactured by Data Physics Corporation (24 bit ADC, 120 dB dynamic range and 
110 dB anti-alias filters). Output units are in volts.

Acquisition Parameters – Minimum sampling rate of 25.6 Hz with time windows 
continuously adjusted by the analyzers for each frequency increment. Data 
provided in frequency domain only (i.e., linear spectrum from 10 – 1 Hz for each 
receiver).

Data Description – For both data types (Ascii and Matlab), files are organized 
in folders based on source-offset location. For the Ascii data, a single row 
header is provided at the top of the file to identify each column. Column 1 is a 
frequency vector with units of Hz, while columns 2-43 contain the complex 
numbers of the linear spectrum for each receiver (CH01 real – CH21 imag). The 
real and imagery parts of the linear spectrum for each channel are tabulated 
separately in alternating columns, such that column 2 and column 3 contain the 
real and imaginary components, respectively, for receiver 1. For the Matlab 
data, a frequency vector named “Frequency” and a matrix containing the linear 
spectra named “Data” are provided. The linear spectra are saved in the complex 
double format with both real and imagery parts in the same column. Column 1 of 
the Data matrix contains the linear spectrum of channel 1 (CH01) and columns 
2-21 represent the spectra of channels 2-21, respectively.
