MB-System Unix Manual Page: mbsegygrid

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    mbsegygrid
    Section:  MB-System 5.0  (1)
    Updated:  26 October 2009
    Index

    NAME

    mbsegygrid - Generate time vs. trace number grids of seismic data from segy files.

    VERSION

    Version 5.0

    SYNOPSIS

    mbsegygrid -Isegyfile -Ogridfile
    [-Ashotscale/timescale -Bmaxvalue/window -Ddecimatex/decimatey
    -Gmode/gain[/window]
    -Smode[/start/end[/schan/echan]] -Tsweep[/delay]
    -Wmode/start/end -H -V]";

    DESCRIPTION

    MBsegygrid generates grids of seismic data from segy files.
    The program works by inserting trace data into a grid in
    which the y-axis is some measure of trace number, range, or distance
    along a profile, and the y-axis is time. The output files are GMT netCDF
    format grid files.

    The x-dimension of the grid is determined by the number of traces specified
    by the -S option and any decimation specified with option -D. The
    y-dimension of the grid is determined by the sample spacing, any decimation
    specified with option -D, and the time sweep specified by the  -T
    option.

    If the -S option is not specified, then all of the traces in the segy file
    will be gridded. If the time sweep and delay (if any) are not specified using
    the -T option, then the sweep and delay will be set so that all trace samples
    are incorporated into the grid.

    A simple time-varying gain can be applied to the traces before gridding using
    the -G option. The start time for the gain may be either the start
    of the trace or the seafloor arrival time.

    Regions of the grid without data are indicated in the output by NaN values.

    AUTHORSHIP

    David W. Caress (caress@mbari.org)

      Monterey Bay Aquarium Research Institute

    Dale N. Chayes (dale@ldeo.columbia.edu)

      Lamont-Doherty Earth Observatory

    OPTIONS

    -A

    shotscale/timescale

    This option causes the x-axis to be rescaled from shot number to distance in meters
    and the y-axis to be rescaled from time in seconds to depth in meters.
    The shotscale value represents the shot spacing in meters and the
    timescale value is the scaling from time to depth (typically 750 m/s
    for the water column).
    -B

    maxvalue[/window]

    This option causes the application of automatic gain control (AGC). At each sample, a time interval
    window seconds long centered on the sample is considered. The sample value is multiplied
    by a scaling factor calculated as maxvalue divided by the maximum original value in the
    time interval. This approach can emphasize coherent arrivals regardless of amplitude level. If
    window is not specified, then the window is taken to be the trace length in time so that
    the entire trace is normalized using the same scale factor, and all traces has the same maximum
    value of maxvalue.
    -D

    decimatex/decimatey

    Sets the decimation of traces (decimatex) and samples (decimatey) used in
    generating the output grid. The downsampling of the data is actually accomplished by averaging
    the values within each grid bin rather than omitting traces or samples.
    -G

    mode/gain[/window]

    Sets the application of gain to the trace data. The mode value determines how
    the gain is applied. If mode = 0, no gain is applied.If mode = 1,
    the gain is applied starting from the beginning of the trace. If  mode = 2,
    the gain is applied starting at the seafloor (assuming that a seafloor pick has
    been defined in the segy data file). The gain value sets the gain applied
    as follows. If G = gain and t is the time in seconds since the start of
    gain application, then each sample is multiplied by a factor of (1 + (G * t)).
    The parameter window, if given, sets the length of the time interval
    in seconds that gain is applied. When the gain is windowed, trace values after
    the end of the gain window are zeroed.
    -H

    This "help" flag cause the program to print out a description
    of its operation and then exit immediately.
    -I

    segyfile

    Sets the filename of the input segy seismic data file to be gridded.
    -O

    gridfile

    Sets the filename for the output GMT netCDF format grid.
    -S

    mode[/start/end[/schan/echan]]

    This option sets the range of traces that are gridded, and thus determines
    the x-dimension of the output grid (also impacted by any decimation
    specified with -D). If mode = 0, then start and end
    refer to shot numbers. This typically is useful for subbottom data or seismic
    data in shot gather form. If mode = 1, then start and end
    refer to CMP (or RP or CDP) numbers. This typically is useful for seismic
    reflection data in stacked or CMP gather forms. If the data are multichannel
    seismic reflection or seismic refraction in either shot or CMP gathers, the
    start and end of the channels selected for gridding is set using the optional schan
    and echan, respectively. The x-dimension of the output grid is determined by
    (end - start + 1) * (echan - schan + 1) / decimatex.
    -T

    sweep[/delay]

    Sets the time range of seismic data to be gridded. The sweep specifies
    the number of seconds of data comprising the y-axis of the grid. The number of
    samples follows from the sample interval of the data, and any decimation
    applied using -D. The optional delay value sets the sweep
    start time, again in seconds.
    The y-dimension of the output grid is determined by
    sweep / sampleinterval / decimatey, where the sampleinterval is
    a parameter read with the seismic data.
    -V

    Normally, mbsegygrid prints out information regarding its
    controlling parameters during execution; the
    -V option causes the program to also print out statements
    indicating its progress.
    -W

    mode/start/end

    This option can be used to limit the data being gridded to a particular time
    window in various ways. This option does not impact the definition of the overall
    grid bounds, but does restrict the data gridded to samples within particular times
    of interest. If mode = 1, then start and end are simply start and end
    times of good data in seconds. If mode = 2, then start and end are relative to
    the time of the bottom return. In this case start is often negative so that the
    grid shows data above the seafloor, and then down into the subsurface. Finally, if mode = 3,
    then start and end are relative to the time corresponding to the sonar
    depth.

    EXAMPLES

    Suppose that we have a Reson 7k format file (format 88) called 20040722_152111.s7k
    that contains subbottom profiler data. Further suppose that we
    have used mbextractsegy to extract the subbottom profiler data
    into a segy format file called 20040722_152111.s7k.segy. MBextractsegy
    also generates a "sinf" file containing statistics about the data in the segy
    file. In this case, the contents of the sinf file 20040722_152111.s7k.segy.sinf are:

            SEGY Data File:      20040722_152111.s7k.segy

            File Header Info:

              Channels:                          1

              Auxilliary Channels:               0

              Sample Interval (usec):           64

              Number of Samples in Trace:     8330

              Trace length (sec):         0.533120

              Data Format:                IEEE 32 bit integer

              CDP Fold:                          0

            Data Totals:

              Number of Traces:               2527

              Min Max Delta:

                Shot number:                    56     2582     2527

                Shot trace:                      1        1        1

                RP number:                      56     2582     2527

                RP trace:                        1        1        1

                Delay (sec):              0.000000 0.000000 0.000000

                Range (m):                0.000000 0.000000 0.000000

                Receiver Elevation (m):   -224.030000 -2.860000 -221.170000

                Source Elevation (m):     -224.030000 -2.860000 -221.170000

                Source Depth (m):         2.860000 224.030000 -221.170000

                Receiver Water Depth (m): 51.510000 487.670000 -436.160000

                Source Water Depth (m):   51.510000 487.670000 -436.160000

            Navigation Totals:

              Start of Data:

                Time:  07 22 2004 15:20:37.029000  JD204

                Lon: -121.8573     Lat:   36.7755

              End of Data:

                Time:  07 22 2004 15:44:15.438000  JD204

                Lon: -121.8572     Lat:   36.7952

            Limits:

              Minimum Longitude:    -121.8574   Maximum Longitude:    -121.8572

              Minimum Latitude:       36.7755   Maximum Latitude:       36.7952

    In order to generate a time vs. trace number grid of all traces in the
    segy file, with a column for each trace and a row for each time sample,
    one can simply invoke mbsegygrid without specifying a range of
    desired traces or the desired time sweep. The program automatically sizes
    the grid to include all traces and samples, taking into account trace start
    delays if necessary. The root of the output grid filename is specified with
    the -O option; if "SubbottomGrid" is specified then the output
    grid will be named SubbottomGrid.grd. The command is:

            mbsegygrid -I 20040722_152111.s7k.segy                  -O SubbottomGrid

    and the output to the terminal looks like:

            MBsegygrid Parameters:

            Input segy file:         20040722_152111.s7k.segy

            Output fileroot:         SubbottomGrid

            Input Parameters:

                 trace mode:         1

                 trace start:        56

                 trace end:          2582

                 channel start:      1

                 channel end:        1

                 trace decimation:   1

                 time sweep:         0.533120 seconds

                 time delay:         0.000000 seconds

                 sample interval:    0.000064 seconds

                 sample decimation:  1

                 window mode:        0

                 window start:       0.000000 seconds

                 window end:         0.000000 seconds

                 gain mode:          0

                 gain:               0.000000

            Output Parameters:

                 grid filename:      SubbottomGrid.grd

                 x grid dimension:   2527

                 y grid dimension:   8331

                 grid xmin:          55.500000

                 grid xmax:          2582.500000

                 grid ymin:          -0.533152

                 grid ymax:          0.000032

                 NaN values used to flag regions with no data

            PROCESS read:0 position:0 rp:56 channel:1 2004/204 15:20:37.029 samples:8330 interval:64 usec minmax: 0.000000 2425.784912

            PROCESS read:25 position:25 rp:81 channel:1 2004/204 15:20:51.068 samples:8330 interval:64 usec minmax: 0.000000 3832.087402

            PROCESS read:50 position:50 rp:106 channel:1 2004/204 15:21:05.106 samples:8330 interval:64 usec minmax: 0.000000 1590.149658

            ....................

            PROCESS read:2475 position:2475 rp:2531 channel:1 2004/204 15:43:46.800 samples:8330 interval:64 usec minmax: 0.000000 991.466064

            PROCESS read:2500 position:2500 rp:2556 channel:1 2004/204 15:44:00.838 samples:8330 interval:64 usec minmax: 0.000000 838.286926

            PROCESS read:2525 position:2525 rp:2581 channel:1 2004/204 15:44:14.877 samples:8330 interval:64 usec minmax: 0.000000 985.870667

            --------------

            Plot generation shellscript <SubbottomGrid.grd.cmd> created.

            Instructions:

              Execute <SubbottomGrid.grd.cmd> to generate Postscript plot <SubbottomGrid.grd.ps>.

              Executing <SubbottomGrid.grd.cmd> also invokes gv to view the plot on the screen.

            --------------

    The size of the the output grid can be checked using the GMT program
    grdinfo. The results of the command:

            grdinfo SubbottomGrid.grd

    look like:

            SubbottomGrid.grd: Title: Seismic Grid from 20040722_152111.s7k.segy

            SubbottomGrid.grd: Command:

            SubbottomGrid.grd: Remark:

                    Projection: SeismicProfile

                    Grid created by MBsegygrid

                    MB-system Version 5.0.4

                    Run by <caress> on <hess> at <Thu Sep 23 16:24:39 2004>

            SubbottomGrid.grd: Pixel node registration used

            SubbottomGrid.grd: grdfile format # 0

            SubbottomGrid.grd: x_min: 55.5 x_max: 2582.5 x_inc: 1 units: Trace Number nx: 2527

            SubbottomGrid.grd: y_min: -0.533152 y_max: 3.2e-05 y_inc: 6.4e-05 units: Time (seconds) ny: 8331

            SubbottomGrid.grd: z_min: 0 z_max: 2623.34 units: Trace Signal

            SubbottomGrid.grd: scale_factor: 1 add_offset: 0

    MBsegygrid also uses the macro mbm_grdplot to generate a shellscript
    called SubbottomGrid.grd.cmd that, when executed, will use GMT commands
    to generate a Postscript plot of the grid.

    In order to generate a grid of a subset of the subbottom data (for instance,
    shots 1500 - 2000 and the time sweep from 0.25 to 0.35 seconds), use the -S
    and -T options:

            mbsegygrid -I 20040722_152111.s7k.segy                  -O SubbottomGrid2               -S0/1500/2000 -T0.1/0.25

    This time the grdinfo output looks like:

            SubbottomGrid2.grd: Title: Seismic Grid from 20040722_152111.s7k.segy

            SubbottomGrid2.grd: Command:

            SubbottomGrid2.grd: Remark:

                    Projection: SeismicProfile

                    Grid created by MBsegygrid

                    MB-system Version 5.0.4

                    Run by <caress> on <hess> at <Thu Sep 23 16:40:34 2004>

            SubbottomGrid2.grd: Pixel node registration used

            SubbottomGrid2.grd: grdfile format # 0

            SubbottomGrid2.grd: x_min: 1499.5 x_max: 2000.5 x_inc: 1 units: Trace Number nx: 501

            SubbottomGrid2.grd: y_min: -0.35 y_max: -0.249968 y_inc: 6.4e-05 units: Time (seconds) ny: 1563

            SubbottomGrid2.grd: z_min: 0 z_max: 558.42 units: Trace Signal

            SubbottomGrid2.grd: scale_factor: 1 add_offset: 0

    SEE ALSO

    mbsystem(l), mbm_grdplot(l), mbmosaic(l), mbm_grid(l)

    BUGS

    This tool isn't close to being complete...

     Index

    NAME
    VERSION
    SYNOPSIS
    DESCRIPTION
    AUTHORSHIP
    OPTIONS
    EXAMPLES
    SEE ALSO
    BUGS

Last Updated: 26 October 2009

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