Ignazio Guerra - Uni. Calabria, 2003
ESTRAI.m - directions for use

MATLAB program ESTRAI.M reads the MARS_88 floppy disk data (binary digital seismic continuous recordings) and outputs a unique file with the desired time-window data. In this way, the following step to built up and visualize the digital seismic record-sections, using an ad-hoc software 'VIDEO.M', will be faster.

The program ESTRAI.M reads other two auxiliary data files (written in BASIC):

1) first file containing the shooting points data: shooting times, coordinates, distances and azimuth (as regards to the recording station). This file is produced by 'MAIRE01.BAS' Basic routine, which furthermore reads as input the navigation data file, given by the offshore shooting Team;
2) a 2nd file with references to the files to be read: 1st line: N_ff (N. of binary files to be read); then 2xN_ff lines follow, each one with a couple of lines: full path of the file and the duration (sec) of the recorded window. This file is produced by another basic routine: 'ESTRLST.BAS'. Reduction seismic velocity Vr is chosen in the 2nd line (Vr=...); by default its value is 6 km/s.

ESTRAI.M asks also for the following:

  • Sh_file: shooting points data filename (file 1);
  • Tr_file: recorded signals index filename (file 2);
  • Sel: selection criteria: '1' = in line profiles (times vs distances plots); '2' = 'fan' profiles (times vs azimuths plots);
  • [only if  Sel=1: D_min, D_max (km); if '2': Az_min, Az_max (deg) ]
  • T_win: time window of the digital waveforms to be processed (sec);
  • N_dec: decimation factor (N_dec=1: all the data files will be read; N_dec=2: file N. 1,3,5,7... will be read);
  • timing correction (it must be ≠ 0) between shooting ship and recording station (such as GMT and local time, or GMT and summer local time, etc.)
  • N_first: number of 1st shot to be read (N_first > 1 in order to skip first N_first-1 shots). Useful when ship is getting near the recording station and then goes away: making two different datasets, it will be possible to plot two section-films with opposite directions;
  • N_sec0: n. of seconds before the zero-time in the record section (with reduced times or not);
  • N_tr: instead of a true recorded seismic signal (a 'trace'), it could be replaced by a 'synthetic' trace (the average of N_tr near signals)
  • A_max: amplitude normalization factor of the signals;
  • Title: title of the desired record-section;
  • Filt: 'butterfly' filter option; if 'y' (yes) the user is requested also for the f_min, f_max, n_order (better reply 'n' (no) because filtering is possible also in the following step VIDEO.M;
  • Save: save option; if 'y' (yes) the user is requested also for the filename to be created.

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