GeophysicalImageProcessingwithSeismicUnixGPGN461/561Lab

John Stockwell

Contact info

John Stockwell Phone: 303-273- 3049Office: GC 260 LEmail: john@dix.mines.eduWeb page: http://cwp.mines.edu/~john

Homework Policy PDF file emailed to:

john@dix.mines.edu No more than 3 pages consisting of: A

short paragraph of commentary, figures properly labeled, commands captured from your screen.

All homework assignments must be turned in. Failure to turn in a single assignment will result in an incomplete for the course.

Chapter 1- Preliminaries

Logging in Shell Working environment Choice of editor

Logging in

You should be able to use your Colorado School of Mines MultiPass password. If you are unable to login, go to another computer where you can login and reset your MultiPass password.

About Unix-like systems and shells

The master program that runs the computer is called the kernel

A shell is a program that interacts with the kernel.

In Unix and Unix-like systems the shell has its own programming language

Choice of editors

We will be working in the Terminal Our mode of operation is typing

commands and editing text files There are many choices of editors

vi exists on all Unix and Unix-like systems, it is hard to learn but easy to use. gedit is easy to learn.

.bashrc and .bash_profile

Your working shell is the bash shell. It has two configuration files: .bashrc and .bash_profile

Add the following lines: export CWPROOT=/usr/local/cwp export PATH=$PATH:$CWPROOT/bin:.

Save and logout completely. Log back in.

Type a few UNIX commands

$ cd change directory $ pwd print current working directory $ ls list contents of current

directory $ df -h disks filled?

Unix man pages

$ man ls $ man cd $ man df $ man bash

$ man ls $ man cd $ man df $ man bash

Make a scratch directory

$ cd /gpfc $ pwd (see where you are at) $ mkdir yourusername

(that is, type: your username on the system)

$ cd /gpfc/yourusername $ pwd

Like scratch paper scratch directories are NOT backed up!

Chapter 2 Getting started with SU and Unix (p.17)

$ cd /gpfc/yourusername $ suplane > junk.su $ suxwigb < junk.su $ suxwigb < junk.su title=Test pattern

label1=time (s) label2=trace number & (type this as one continuous line)

Pipe |, redirect out >, redirect in junk.su (redirect out) $ suxwigb < junk.su (redirect in)

(If you aren't seeing plots on the screen, ask for help!)

Stringing commands together p.20

$ suplane | suspecfx | suxwigb $ suplane > junk.su $ suspecfx < junk.su > junk1.su $ suxwigb < junk1.su label1=freq (Hz)

label2=trace number title=Amplitude spectrum & (type the last one as one continuous line)

Discussion Questions

What is the Fourier Transform? Why does the image of the Fourier

amplitude spectrum appear the way it does?

F =

f t ei t dt

ei t=cos t i sin t

The Forward Fourier Transform

Functions are like vectors (lists of numbers that can be linearly combined)

Integration of the product of two functions is like a dot product

Some functions such as sin and cos act like unit vectors

The Fourier transform decomposes a function into components of sines and cosines of specific frequencies---- just like the components of a vector.

Spike (delta function)? Box function? Gaussian? Cosine? Sine?

Important Fourier Transforms-What is the Fourier transform of:

Chapter 3 Viewing Data

Make a temporary working directory in your /gpfc/yourusername directory

$ cd /gpfc/yourusername $ mkdir Temp1 make directory $ cd Temp1 change directory

(directory means the same thing as folder)

Copying data to your work area

$ cd /gpfc/yourusername

$ cp /data/cwpscratch/Data1/sonar.su .

$ cp /data/cwpscratch/Data1/radar.su .

$ cp /data/cwpscratch/Data1/seismic.su . Make sure you type the dot .

Wiggle trace plots

$ suxwigb < sonar.su & (terrible) (zoom in with the rubberband box)

$ suxwigb < radar.su &

$ suxwigb < seismic.su & In each case, zooming in with the rubberband box shows more traces.

Image plots

$ suximage < sonar.su & $ suximage < radar.su & $ suximage < seismic.su &

Image plots are arrays of numbers represented by a linear distribution of 256 shades of gray. The largest amplitudes may bias the gray scale causing smaller amplitudes not to show.

Sonar data, no display gain.

Sonar data, perc=99

Sonar data, perc=99 legend=1

Greyscale

$ suximage < sonar.su perc=99 & $ suximage < sonar.su perc=99

legend=1 & legend=1 shows the amplitudes perc=99 rejects the top 1 percentile

of amplitude

Normalization: Median balancing

$ sunormalize $ sunormalize norm=med < sonar.su |

suximage legend=1 & $ sunormalize norm=med < sonar.su |

sunormalize norm=rms | suximage legend=1 perc=99 &

Click on a window and type 'h' or 'r'

Homework problem Repeat display experiments with

radar.su and seismic.su Write a short report, not more than 3

pages, including figures (appropriately labeled), the commands you used to get them, and a short (2 or 3 sentences) describing what you observed (think of it as a figure caption.)

Mail to john@dix.mines.edu as a PDF file.

Concluding Remarks

Wiggle trace plots are appropriate for smaller numbers of traces

Image plots may be preferred for larger datasets

Bad choices of normalization or display gain can highlight a desired feature of data, or ruin the presentation of an otherwise properly processed dataset if used improperly.

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