                       Program TracePlot, Version 1.1, 
                 seismic trace plotting program for the Macintosh
                                     By
                                John J. Miller

                             U.S. Geological Survey
                           Open File Report OF-92-xxx

                                    ABSTRACT

     Program TracePlot, Version 1.1, is a Macintosh software application to
access a SEG-Y format seismic data file and display the seismic traces on the
CRT screen of a Macintosh micro-computer.  Both color and monochrome monitors
are supported.  Display modes are Wiggle-trace, Variable Area, or Wiggle plus
Variable Area.  Horizontal and vertical resolution is dependant upon the size
of the monitor that is attached to the computer.  The user controls the
following parameters: 1) number of traces to be displayed on the screen at any
one time, 2) the time window displayed, 3) the seismic trace in the file at
which to begin plotting and trace increment to display thereafter, 4) plot
direction 5) timing-line annotation increment, and 6) type of gain to apply
(either constant gain factor, or trace-by-trace normalization).  A pull-down
menu provides interactive help during program execution.  A utility program is
also included which provides the function of copying a portion of a SEG-Y
format data file to another file.

                                  INTRODUCTION

     Program TracePlot, Version 1.1, accesses a SEG-Y format seismic data file
and display the seismic traces on the CRT screen of a Macintosh
micro-computer.  The program was developed on a Macintosh IIx using the
Microsoft QuickBasic, version 1.0 compiler.  This program is equivalent to the
SEG-Y display program, PLOTSEGY for DOS-based computers (Zihlman, 1992).

     TracePlot is quite flexible and provides a number of options which allow
the user to display the seismic traces in different ways.  The parameters which
the user can control are described in the section entitled "The Parameter Input
Screen."  During program execution, the user can get help on any of the
parameters by utilizing a pull-down menu.

     A utility program, called TraceCopy, Version 1.1 is also included and will
copy a portion of a SEG-Y format data file to another file.  A subset of the
traces in the file and/or a subset of the samples in the traces can be copied.
Thus, large files can be separated into smaller-size files which can more
easily be transferred to floppy disk, or transmitted over a network.

     This document assumes that the user is familiar with the operation of
Macintosh applications, specifically keyboard entry of text in standard
Macintosh requestor boxes, and the use of the mouse pointer to make selections
on the screen and to access pull-down menus.

     The programs are invoked by double clicking the mouse pointer on the
program's Icon, or selecting the Icon with a single click and then selecting
OPEN from the FILE menu.

                                   TERMS USED

     A number of terms related to the geophysical Industry and specifically
seismic data processing and interpretation are used in this report and are
defined below.  Refer to Figure 1 for examples of some of these terms.  Some
definitions were taken from The Encyclopedic Dictionary of Exploration
Geophysics (Sheriff, 1976), which provides a comprehensive list and definitions
of geophysical terms.

Trace              A record of one seismic channel, either unprocessed or
                   processed.

Trace-sequential   A format by which all samples of an individual trace are
                   stored without interruption from minimum to maximum travel
                   time, followed sequentially, by other traces (sometimes
                   called demultiplexed format).  SEG-Y format is designed to
                   store data in trace-sequential format.  The opposite of
                   trace sequential is multiplexed format whereby all samples
                   from the same travel time are stored without interruption
                   from low channel to high channel.

Gather             A group of traces related by some common attribute (e.g. a
                   shot gather is all the traces recorded from the same shot; a
                   CDP gather is all the traces that map the same Common Depth
                   Point, etc.).

Wiggle trace       A method of displaying a seismic trace whereby a continuous
                   solid line is drawn connecting each sample to the next.

Variable Area      A method of displaying a seismic trace whereby only samples
                   having positive values are drawn and the area between 0
                   amplitude and the positive value is filled in by a solid
                   color.

Trace Width        The distance between the origin of one trace and the origin
                   of the adjacent trace on a seismic display.

                SOFTWARE/HARDWARE REQUIREMENTS AND AVAILABILITY

SOFTWARE/HARDWARE

     TracePlot, Version 1.1 is a Macintosh application designed to display the
seismic traces contained in a SEG-Y format disk file on the CRT screen of a
Macintosh micro-computer.  User-controlled options are available to specify
display parameters like scale, gain, plotting style, timing line annotation,
plot direction, etc.  Color and Monochrome monitors are supported.

     TraceCopy, Version 1.1 is designed to copy a portion of a SEG-Y format
disk file to another file.  A subset of the traces and/or a subset of the
samples from the input file can be copied to another, smaller file which will
allow transfer of the data using floppy disks or other media having limited
storage capacity.

     Input files must be in standard SEG-Y format as specified by the Society
of Exploration Geophysicists (Barry, et al, 1975).  TracePlot requires that the
data samples be type #1: IBM floating point (4 bytes(32-bits) per sample);
TraceCopy requires that the data samples be either type #1 or type #2: IBM
fixed point (4 bytes/sample).

     The programs were developed on a Macintosh IIx using the Microsoft
QuickBasic, version 1.0 compiler, binary math version, and are designed to run
on any standard Macintosh computer, using operating system 6.0, or higher.  It
is possible that the programs will run on Macintoshes running operating systems
released prior to system 6 but this has not been tested.  Many of the newer
Macintosh computers available at the time of publication (those that have a
68030 or higher processing chip), use 32-bit addressing which will cause
TracePlot and TraceCopy to fail, giving a system error #1.  If such an error
occurs, the programs can be successfully executed by disabling 32-bit
addressing in the following manner:

1.  Open the "apple" menu at the upper left of the main screen

2.  Open the control-panel

3.  Open the Memory icon

4.  Click 32-bit addressing button to "off"

5.  Restart the machine to invoke this option

     After performing the above 5 steps, the programs should execute
successfully.

HARDWARE-SPECIFIC VERSIONS

     Four versions of TracePlot are provided.  Their names and hardware
requirements are as follows:

1.  TracePlot-bw:  This version should work on all Macintoshes including those
     with only monochrome screens (black and white).  The background of the
     screen is set to white and the foreground is set to black.

2.  TracePlot:  This version should work on all Macintoshes that have a color
     monitor.  The background color is set to blue and the foreground color is
     set to white.

3.  TracePlot-68020:  This version is the same as #2 above, except that it
     contains optimized code that allows it to run faster on a machine that has
     a 68020 processing chip.  It should also run on machines that do not have
     a 68020 chip.

4.  TracePlot-68881:  This version is the same as #3 above, except that a 68881
     math coprocessor chip MUST be present in order for the program to run and
     thus the program will execute faster than the other versions.

                       EXPECTED DATA FILE FORMAT (SEG-Y)

     The SEG-Y seismic data format standard was developed by the Society of
Exploration Geophysicists (SEG) in 1975 and has been in common use throughout
the geophysical industry since that time.  A complete description of the SEG-Y
format is given in Barry, et al (1975).  That document assumes 9-track,
magnetic tape recording media.  TracePlot and TraceCopy, Versions 1.1 expect as
input, a disk-image of the SEG-Y data format described therein.  Naturally, the
inter-record and inter-block gaps described for magnetic tape media, will not
exist on the disk-image.  Thus, the programs expect a continuous file composed
of a 3200-byte EBCDIC header, a 400 byte binary header, and data traces, each
composed of a 240 byte trace-header followed by a fixed number of seismic data
samples.

     The SEG-Y format provides for four (4) different sample types:

1. Floating point (4 bytes (32-bits) per sample),

2. Fixed point (4 bytes/sample),

3. Fixed point (2 bytes/sample), and

4. Fixed point with gain code (4 bytes/sample).

     TracePlot, Version 1.1 is designed to display SEG-Y data samples that
conform to the type 1, 32-bit floating point format in which each data value is
recorded in four successive bytes in IBM compatible floating point notation as
defined in IBM Form GA 22-6821 (Barry, et al, 1975).  Sample type 1 is by far,
the most commonly used version of SEG-Y; however, it is planned that future
versions of the program will be able to access sample types 3-4.

     TracePlot, version 1.1 uses binary math (IEEE standard) to internally
represent integer and floating point numbers.  IEEE-format represents numbers
differently from IBM-format and thus TracePlot cannot read the IBM-format
numbers directly from disk.  Each header value and data sample is read
byte-by-byte (as characters, rather than numbers) and the integer or floating
point value is reconstructed according to the IBM standard.  The resulting
numbers are stored in IEEE-format for internal use.  Interested readers can
refer to the source code (subroutines Make2Byte, Make4Byte, and ReadTrace) for
the method used.  Zihlman (1992) gives a complete description of a method to
convert the 32-bit IBM standard an IEEE 32-bit floating point number for
computers running the DOS operating system.

     TraceCopy, version 1.1 performs a byte-by-byte copy and hence has no need
to perform numeric conversions.  Because of this feature, TraceCopy can also be
used to copy SEG-Y format files that use sample type 2, as these samples are 4
bytes in length.[PB]


 [WS 5 in]


*Figure 1.  Seismic traces displayed using the display styles of Wiggle-trace
(left), Variable-Area (center), and Variable-Area plus Wiggle-trace (right).  A
number of terms used in the text are illustrated by annotations on this figure.

                                  SOURCE CODE

     The source code for TracePlot and TraceCopy is provided on the diskette in
files TracePlot.bas and TraceCopy.bas, respectively.  These files are contained
in the folder named Source-Code.  Interested readers can inspect these files by
importing them into most commercial word processing programs.  Readers who have
the QuickBasic compiler can use the compiler to access these files.

             [PB]TRACEPLOT, VERSION 1.1; USER'S GUIDE AND TUTORIAL

     The following sections describe the features and operation of TracePlot,
version 1.1.  These descriptions are performed by means of tutorial
instructions on how to plot the sample data file StackData (included on the
diskette).  Except for items specific to the actual plotting of the data, many
of the sections contain information that is also relevant to TraceCopy, the
file copy utility program (parameter input screen, start and stop Plotting
(copying), etc.).  Details of TraceCopy are given in the last section of this
document.

INSTALLATION

     TracePlot and TraceCopy can be executed directly from the diskette
included with this publication.  However, it is recommended that you install
the programs on a hard disk.  It is also recommended that you make a copy of
the diskette and use that copy to continue with this installation and/or to
perform the plotting of the sample SEG-Y data file.  Keep the original diskette
as a backup.  Refer to your Macintosh User's guide for instructions on how to
duplicate a 3.5 " disk.

     To install the program on a hard disk, create a new folder on the hard
disk.  Decide which hardware-specific version of TracePlot you wish to install
and copy that file to the new folder.  Next, copy files TraceCopy and StackData
to the folder.  Installation is complete.

PLOTTING THE SAMPLE SEG-Y FORMAT DATA FILE

     File StackData is a SEG-Y format file, and can be used to test the
operation of TracePlot and TraceCopy.  This file contains a number of "stacked"
seismic traces which are the final product of a typical sequence of seismic
data processing steps.  Each trace contains 1,500 samples at a 4 ms sample
interval.  Thus the maximum time of any one trace is 5996 msec ( (1,500-1)*4
).  The following sections of this user's guide assume that you will be
plotting file StackData.  Any other SEG-Y format data file that you might have
can be plotted by substituting its name for StackData in the following
instructions.

     Start TracePlot by either clicking the mouse pointer twice on its Icon, or
clicking once on its icon, and then selecting OPEN from the FILE menu.  A
welcome screen will appear; click on the button labeled "Continue" or wait a
few seconds; the parameter input screen will appear and a File-Open Dialog box
will appear.

THE PARAMETER INPUT SCREEN

     The Parameter Input Screen (Figure 2) contains requestor boxes and
"buttons" which allow the user to control various parameters for plotting.  Two
small windows will be displayed at the bottom of the screen.  The left window
contains global parameters determined from the header of the current SEG-Y data
file.  The right window is used to display help and error messages.  The
following are details of each parameter.

1.  FILE NAME:  The file name that contains the SEG-Y data. This can be any
valid Macintosh file name that actually exists.  This file is selected from the
File-Open dialog box which appears at the beginning of the program, or from
selecting the File-Open menu (see below).

2.  FIRST TRACE:  The SEQUENTIAL trace in the file to display at the left or
right edge of the plotting screen.  Example:  If the file contains shot gathers
composed of 96 traces each and you wish to begin plotting at the second shot
gather, type 97 for this parameter.

3.  MINIMUM TIME:  The time at the top of the display, in ms. This time must be
>=0 AND <= the maximum time of a trace.  The lower left message window will
display the maximum trace time of the current file.

4.  MAXIMUM TIME:  The time at the bottom of the display, in ms. This value
must be > minimum time. If this value is greater than the maximum trace time,
then the display will be compressed in the vertical direction.  The vertical
exaggeration of the display can be controlled by appropriate use of this
parameter, in combination with the parameters 1) minimum time, 2) maximum
traces on screen, and 3) trace increment.

5. GAIN:  Two methods of defining the gain factor are available:

Normalization:  Type NORM (or any word beginning with the letter n) to invoke
this option.  This option will "normalize" EACH trace before plotting using the
following method:  The absolute value of each sample between the minimum and
maximum times specified, is calculated; the maximum of these values is set
equal to the value of the Overlap parameter, described below.  Thus if overlap
= 1.2, the maximum amplitude of each trace will be plotted 1.2 trace-widths to
the left or right of its origin (0-amplitude).  This option does not preserve
the relative amplitudes between traces, but is a useful option to use when
displaying data that have large amplitude differences from trace to trace, like
unscaled shot gathers.

Scalar Multiplier:  The scalar by which to multiply all sample values of all
traces, prior to plotting.  This value can be any integer or floating-point
number.  If you type a negative value, the polarity of the traces will be
reversed.  This method of scaling preserves the relative amplitudes between
traces.  The following method is used:  The first trace to be plotted
(parameter FIRST TRACE, above) is analyzed.  A "baseline" scale factor is
calculated such that the average of the absolute value of all non-zero samples
will be plotted at 1/2 of a trace width to the left or right of 0-amplitude.
This baseline scale factor is then multiplied by the GAIN specified and this
final GAIN factor is multiplied to all samples plotted.

6.  TIMING LINES:  The increment, in ms, to draw timing lines. Example:  100
means to draw timing lines at integer multiples of 100 ms (100, 200, etc.).

7.  MAXIMUM TRACES ON SCREEN:  The number of traces to plot on the screen.  The
larger that this number is, the closer together the traces will be plotted.
The vertical exaggeration of the display can be controlled by appropriate use
of this parameter in combination with the parameters 1) minimum time, 2)
maximum time, and 3) trace increment.

8.  OVERLAP:  This parameter is used differently depending on the value GAIN,
described above.

For GAIN = NORM:  Overlap is the distance from 0 amplitude, in terms of trace
widths, of the normalized, maximum amplitude of each trace.  Thus, if overlap =
1.5, the maximum amplitude of each trace will be plotted 1.5 trace widths to
the left or right of its 0 amplitude point.

For GAIN = any number:  Overlap is the maximum excursion to the left or right
of 0 amplitude for any one trace, in terms of trace widths.  Thus, if this
number is 1.5, then any amplitude of a trace that would be plotted greater than
1.5 trace widths away from its origin (0-amplitude) will be truncated to that
distance.

9.  TRACE INCREMENT:  The increment at which to display traces, beginning at
the 1st trace.  Example:  if this parameter is specified as 3 and the first
trace to be displayed is 5, then traces 5, 8, 11, .. . , etc. will be
displayed.  The vertical exaggeration of the display can be controlled by
appropriate use of this parameter in combination with the parameters 1) minimum
time, 2) maximum time, and 3) maximum traces on screen.

10.  PLOTTING STYLE:  The style in which the traces are drawn.  Figure 1 show
examples of the types of plotting styles available.  Click on the left-most
button, labeled WG to plot Wiggle-traces only.  Click on the middle button,
labeled VA, for the Variable-Area style: No negative trace samples are plotted
and the area between 0 amplitude and the positive trace samples will be filled
in.  Click on the right-most button, labeled VA+WG to overlay a wiggle trace on
top of a Variable-Area display.

11.  PLOT DIRECTION:  The direction of progression for plotting the traces:
Click on the left-most button, labeled L-R to plot the first trace at the left
edge of the screen and plot subsequent traces sequentially to the right.  Click
on the right-most button, labeled R-L to plot from the right edge to the left.


 [WS 4 in]


*Figure 2.  Example of the Parameter Input Screen.  Parameters displayed are
default values that were determined from the header of the sample SEG-Y format
data file.  The lower right window displays a help message describing the
timing line increment parameter.

SELECT THE SEG-Y FILE

     At the beginning of the program, a standard File-Open Dialog box will
appear.  Files in the folder from which the program was started will be listed
in the menu.  This dialog box also allows access to files in different folders
or on different disks.  Select the file named StackData, then click on the Open
button.  If you click on Cancel before opening a file, the program will require
that you either End the program, or select a file.  If you have already opened
a file, you can open a new file by choosing the File-Open Menu.  The above
described dialog box will reappear.

     Once the file is opened, its header is read and the number of samples per
trace and sample interval is determined.  These are listed in the box at the
lower left of the screen.  If these values are unreasonable, possibly because
they were not stored properly in the header, you will be given the opportunity
to either provide these parameters directly, or to select a new file.  For file
StackData, the header is valid and the values contained within it are
reasonable and so the above mentioned problem will not occur.

THE PDF FILE

     After the file is opened successfully, the program will attempt to open a
file with the same name as the SEG-Y data file, but with an extension of
".PDF".  For file StackData, the PDF-file will be named StackData.PDF; if the
file was named SEGYDATA.SGY, the PDF-file will be named SEGYDATA.PDF, etc.
This file is called the Parameter Definition File (referred to a the PDF-file),
and contains the plotting parameters used the last time that the data file was
plotted.

     Of course, the first time that a data file is plotted, its corresponding
PDF-file will not exist.  The program will determine plotting parameters, based
on the number of samples per trace and sample interval, and these parameters
will be listed on the screen as initial defaults.

     If the PDF-file already exists, the parameters contained within it will be
read and transferred to the screen to be used as initial defaults.  When
plotting begins, the PDF-file will be updated with the latest plotting
parameters.

MODIFY PLOTTING PARAMETERS

     The user may modify any of the plotting parameters listed on the Parameter
input screen, by typing the new parameter in the appropriate requestor box or
clicking on the appropriate button.  For all requestors, there are three ways
to tell the program to accept the value typed:

1.  Press the return key.  Control will be transferred to the next requestor in
     the list (or the top requestor box if the current requestor is at the
     bottom of the list).

2.  Click the mouse on the Accept button to the right of the requestor.  This
     action is equivalent to pressing the return key.

3.  Click the mouse in another requestor:  Control will be transferred to that
     requestor.

BEGIN PLOTTING

     After entering the desired plotting parameters, click the Plot button near
the top of the screen.  The plotting parameters will be analyzed and if they
are acceptable, the screen will clear and the plotting will begin.  If any
errors are discovered, a message will appear in the box at the lower right of
the screen and control will be transferred to the requestor that must be
changed.  The following will be checked before plotting:

1.  Minimum plot time is >=0
2.  Minimum plot time is <= Maximum time of any sample in a trace
3.  Maximum plot time is > Minimum plot time

     If any of the above are not true, then a "beep" will sound, a warning
message will appear in the lower right message box, and control will be
transferred to the appropriate requestor box.

AUTOMATIC STOP OF THE PLOTTING

     Plotting will stop if either 1) the end of the data file is reached or 2)
the screen is completely filled with traces.  If the end of the file is
reached, a message to that effect will appear on the bottom line of the screen;
press any key to return to the parameter input screen.  If the screen is
completely filled with traces and there are more traces in the file left to
display, a message to that effect will appear on the bottom line of the
screen.  Press ESC to return to the parameter input screen; press any OTHER key
clear the display and continue plotting with the next available trace.

FORCE THE PLOTTING TO STOP

     When plotting begins, you can temporarily stop plotting by pressing the
Escape key.  Plotting will stop after the current trace is displayed and a
message will appear at the bottom of the screen.  If you press Escape again,
the parameter input screen will appear; if you press any OTHER key, plotting
will resume with the next available trace.  You can also choose the menu item
entitled "Stop Plotting" to return to the parameter input screen immediately
after the current trace is displayed.  When the parameter input screen
reappears, any of the parameters listed can be changed and the plot can be
restarted.

END THE PROGRAM

     Choose the menu item entitled "End" at any time, or click in the Quit
button on the parameter input screen.

ERRORS DURING PLOTTING

Recoverable Error:  A scale-factor error can occur if you are using a Gain
factor that preserves relative amplitudes between traces, and the first trace
to be plotted does not have any non-zero samples in the time window specified.
If this error occurs, a window will appear on the screen and you will be
instructed to provide a different trace as the 1st trace to be plotted.

Unrecoverable Errors:  Most unrecoverable errors are related to numeric
overflows in the data samples.  This can occur when the gain factor specified
is too large, if the file being plotted is corrupted, or if the file is not
really a SEG-Y data file.  If an unrecoverable error occurs, a window will
appear, informing you of the error and you will have to restart the program.

LIMITATIONS

1.  Screen Savers:  Many users install a screen saver program on their
Macintosh system to avoid pixel burn-out of the monitor.  If a screen saver
program covers the screen while either TracePlot or TraceCopy is running, the
screen will not be restored properly when the screen saver stops.  Thus the
user should disable any screen saver programs before executing TracePlot or
TraceCopy for an extended period of time.

2.  Initial Help Request:  On some Macintoshes, if the user chooses a help item
from the pull-down menu immediately after beginning the program, keyboard
control of the initial requestor box may be lost.  If such a situation occurs,
click the mouse pointer on any other requestor, or button, and control should
be returned.

3.  Screen Size:  The programs automatically detect the size of the screen
attached to the computer and attempt to adjust the items on the parameter input
screen and size of the seismic display accordingly.  However, if the screen is
extremely small, such as with a Macintosh Classic, the resolution of the
seismic display may be too limited to be useful.

4.  Invalid Input File Format:  Both TracePlot and TraceCopy will open any
input file selected.  Checks are made to be verify that the sample interval,
number of samples and length of the file based on those parameters are
reasonable (i.e. the file is large enough to contain at least one seismic
trace).  However, it is possible that reasonable values for these three
parameters could exist in any file.  In that case, the programs will attempt to
copy or plot the data contained in the file, with unpredictable results
(although usually a data overflow error will occur when plotting).
Furthermore, if the programs determine that the above three parameters are
unreasonable, the user is given the opportunity to provide a sample interval
and number of samples per trace directly.  Once reasonable parameters are
provided, the program will then plot, or copy the data.  For example, it is
even possible to provide the application's source code (TracePlot.bas) as
input, and attempt to plot it as seismic data.

                    [PB]TRACECOPY, VERSION 1.1; USER'S GUIDE

     The operation of TraceCopy, Version 1.1, is very similar to that of
TracePlot.  The parameter input screen is much simpler because parameters
specific to plotting are eliminated (plotting style, plot direction, timing
line annotation increment, gain, and overlap between adjacent traces).   A
parameter for the output file name is added.

     The remaining plotting parameters in TracePlot are used as copying
parameters in TraceCopy:

1.  The sequential trace in the data file to COPY first
2.  The Minimum COPY time, in milliseconds
3.  The Maximum COPY time, in milliseconds
4.  Total number of traces to COPY
5.  The trace increment for COPYing

     As with TracePlot, you must first select the input file.  TraceCopy does
not use a PDF-file;  default parameters are calculated from the number of
samples/trace and sample interval stored in the file's header.  As with
TracePlot, if file's header contains unreasonable values, you will have the
opportunity to provide these parameters directly.  You can modify the copying
parameters, and then provide a name for the output file.

     To begin the copying process, click the copy button near the top of the
screen.  The program will check the copying parameters to make sure that the
minimum and maximum times are within the actual data range and that the maximum
time is >= minimum time.  Next the specified output file is checked; if a file
having the same name already exists (and is not empty), you will be given the
opportunity to either overwrite the file, append traces to the end of the file,
or provide a new file name.  If you decide to append traces to the end of an
existing file, those traces must have the same number of samples, and sample
interval as the original file.  No other checks are made prior to beginning the
copy process.

     The 3200-byte descriptive header block is copied without change from the
input file.  The 400-byte header will also be copied without change, unless the
number of samples per trace being copied is different from the original file.
In that case the appropriate value in the header is changed.  The corresponding
value in each trace's header will also be changed.  An exception is that if you
are appending traces to an existing file, the header of the input file will not
be copied.

     The copying can be paused and/or stopped, and the program can be ended, in
the same way that plotting is paused, stopped, and ended.

                                   REFERENCES

Barry, K.M., Cavers, D.A. and Kneale, C.W., 1975, Recommended standards for
     digital tape formats, in Digital Tape Standards; Society of Exploration
     Geophysicists ["Recommended standards for digital tape formats" reprinted
     from Geophysics, v. 32, p. 1073 - 1084; v. 37, p. 36-44; v. 40, p.
     344-352.] p. 22-30

Zihlman, F.N., 1992, PLOTSEGY, V1.0: A DOS graphics program to display SEG-Y
     disk-image seismic data; U.S. Geological Survey Open File 92-349A and
     92-349B.

Sheriff, R.E., 1976, Encyclopedic dictionary of Exploration Geophysics, Society
     of Exploration Geophysicists, Tulsa, OK, 266 p.
