MB-System Unix Manual Page: mbsegypsd

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    mbsegypsd
    Section:  MB-System 5.0  (1)
    Updated:  24 December 2009
    Index

    NAME

    mbsegypsd - Calculates the power spectral densisty function (PSD) of each trace in a
    segy file, outputting the PSD estimates as a GMT grid file with trace number along
    the x axis and frequency along the y axis.

    VERSION

    Version 5.0

    SYNOPSIS

    mbsegypsd -Ifile -Oroot
    [-Ashotscale -Ddecimatex -R
    -Smode[/start/end[/schan/echan]] -Tsweep[/delay]
    -Wmode/start/end -H -V]";

    DESCRIPTION

    mbsegypsd calculates the power spectral densisty function (PSD) of each
    trace in a segy file, outputting the PSD estimates as a grid with
    trace number along the x axis and frequency along the y axis.
    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.
    If the -S option is not specified, then all of the traces in the segy file
    will be processed. 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.

    The y-dimension of the grid is determined by the sample interval in the time series
    data. The frequency range runs from zero Hz to a maximum frequency given
    in Hz by 1/(2*sampleinterval), where the sampleinterval is in seconds. So,
    for instance, hydrophone data sampled at 26 kHz (26000 samples/second) will
    have a sample interval of (1/26000 = 0.00003846 seconds). In this case, the
    PSD will be calculated for frequencies ranging from 0 Hz to 13000 Hz (13 kHz).

    For each trace, the PSD will be calculated by ensemble averaging, which means that
    the trace will be broken up into a number of segments of length nfft (specified
    with the -N option, default = 1024), a fast-Fourier-transform (FFT) will be
    calculated for each segment, and the PSD estimate will be the average of
    the FFT magnitudes over all segments. Before the FFT is calculated, each segment
    is multiplied by a Hanning (cosine) taper; the PSD estimates are normalized to
    account for the loss of signal due to the taper application.

    The output grid can be either in linear units (Intensity/Hz) or in log-scaled dB/Hz
    calculated as 20 * log10 (raw-PSD-value). The default is the former, and the
    -L option causes output in the dB/Hz form.

    A shellscript invoking GMT programs to plot the PSD grid is automatically
    generated.

    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

    This option causes the x-axis to be rescaled from shot number to distance in meters.
    The shotscale value represents the shot spacing in meters.
    -D

    decimatex

    Sets the decimation of traces (decimatex) used in generating the output grid.
    -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.
    -L

    Sets the PSD grid output to be in dB/Hz.
    -O

    root

    Sets the filename root 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]

    The sweep value sets the time range of seismic data to be processed in seconds.
    The optional delay value sets the sweep start time, again in seconds.
    -V

    Normally, mbsegypsd 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 processed 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 processed 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 one has a segy file of hydrophone data sampled at a
    37 microsecond interval, corresponding to a 27027 Hz sampling rate.
    Each of 1610 traces consists of 64865 samples. In order to create a
    sonogram displaying the power spectral density as a function of
    time, execute mbsegypsd as follows:

            mbsegypsd -I 20090922_1833_V3422_S7_CH025ms.segy -N1024 -L -O testpsd -V

    Here the -N option sets the FFT dimension used to be 1024 samples, which
    means that the PSD estimate for each trace is the average of 64865 / 1024 = 63
    calculations. The shell output of the program is:

            Program mbsegypsd

            Version $Id: mbsegypsd.c 1770 2009-10-19 17:16:39Z caress $

            MB-system Version 5.1.2beta12

            MBsegypsd Parameters:

            Input segy file:         20090922_1833_V3422_S7_CH025ms.segy

            Output fileroot:         testpsd

            Input Parameters:

                 trace mode:         0

                 trace start:        0

                 trace end:          1609

                 channel start:      1

                 channel end:        1

                 trace decimation:   1

                 time sweep:         2.399968 seconds

                 time delay:         0.000000 seconds

                 sample interval:    0.000037 seconds

                 window mode:        0

                 window start:       0.000000 seconds

                 window end:         0.000000 seconds

            Output Parameters:

                 grid filename:      testpsd.grd

                 psd filename:       testpsd_psd.txt

                 x grid dimension:   1610

                 y grid dimension:   513

                 grid xmin:          -0.500000

                 grid xmax:          1609.500000

                 grid ymin:          -13.171066

                 grid ymax:          13500.342448

                 NaN values used to flag regions with no data

                 shotscale:          1.000000

                 frequencyscale:     1.000000

            PROCESS read:0 position:0 shot:0 channel:1 2009/265 18:32:59.000 samples:64864 interval:37 usec minmax: -102498.789062 -187.008667

            PROCESS read:25 position:25 shot:25 channel:1 2009/265 18:34:14.000 samples:64864 interval:37 usec minmax: -201902.890625 9166.462891

            PROCESS read:50 position:50 shot:50 channel:1 2009/265 18:35:29.000 samples:64864 interval:37 usec minmax: -203695.765625 28316.906250

            PROCESS read:75 position:75 shot:75 channel:1 2009/265 18:36:44.000 samples:64864 interval:37 usec minmax: -201434.375000 24819.115234

            PROCESS read:100 position:100 shot:100 channel:1 2009/265 18:37:59.000 samples:64864 interval:37 usec minmax: -16544.123047 37.462040

            ............................

            PROCESS read:1500 position:1500 shot:1500 channel:1 2009/265 19:47:59.000 samples:64864 interval:37 usec minmax: -8367.179688 -876.420044

            PROCESS read:1525 position:1525 shot:1525 channel:1 2009/265 19:49:14.000 samples:64864 interval:37 usec minmax: -9163.580078 201.037201

            PROCESS read:1550 position:1550 shot:1550 channel:1 2009/265 19:50:29.000 samples:64864 interval:37 usec minmax: -12128.291016 -993.766357

            PROCESS read:1575 position:1575 shot:1575 channel:1 2009/265 19:51:44.000 samples:64864 interval:37 usec minmax: -67764.585938 2457.883789

            PROCESS read:1600 position:1600 shot:1600 channel:1 2009/265 19:52:59.000 samples:64864 interval:37 usec minmax: -190216.031250 -14304.720703

     .br

     .br
    The output PSD grid file is named testpsd.grd. A shellscript named
    testpsd.grd.cmd is also created that, when executed, will generate a plot of the
    sonogram. MBsegypsd also outputs an ascii file containing the average PSD for the
    entire segy file in the form of frequency PSD pairs. In this case, the average PSD file
    is named testpsd_psd.txt, and has contents like:

            0.000000 193.762464

            26.342132 99.114274

            52.684263 93.781880

            79.026395 86.775795

            105.368526 80.297280

            131.710658 74.908340

            158.052790 71.366137

            184.394921 70.319082

            210.737053 69.840534

            237.079184 70.794517

            263.421316 72.002905

            289.763448 71.979001

            316.105579 70.637717

            342.447711 69.652364

            ..............

            13329.118592 -13.659568

            13355.460724 -13.722928

            13381.802855 -12.981740

            13408.144987 -12.626286

            13434.487119 -12.533222

            13460.829250 -13.659002

            13487.171382 -24.474310

    A shellscript named testpsd_psd.txt.cmd is created that will, when executed, generate
    a plot of the average PSD.

    SEE ALSO

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

    BUGS

    Probably...
    The plots could be better...

     Index

    NAME
    VERSION
    SYNOPSIS
    DESCRIPTION
    AUTHORSHIP
    OPTIONS
    EXAMPLES
    SEE ALSO
    BUGS

Last Updated: 24 December 2009

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