geoscixyz / gpg

Geophysics for Practicing Geoscientists

GPG: Geophysics for Practicing Geoscientists

A learning resource for applied geophysics.

Originally created by Douglas W. Oldenburg and Francis H.M. Jones

http://gpg.geosci.xyz

For Developers:

Here are a couple resources on sphinx and reStructured Text:

• http://sphinx-doc.org/markup/
• http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.html

Best practices for attribution:

• https://wiki.creativecommons.org/wiki/Best_practices_for_attribution

Tips:

Example of how to reference a Figure.

• Insert and name your Figure

 .. figure:: ./ExampleImage.png
	:align: center
	:scale: 110%
	:name: ExampleImage

	Figure Caption.

• Reference the Figure

An example image is shown in :numref:`Positive_magnetic_pole`.

Output: An example image is shown in Fig. #.

gpg's Issues

Missing Diagram in Seismic-Refraction-PlusMinus page

gpg/content/seismic/refraction/seismic_refraction_irregular_layers.rst
http://gpg.geosci.xyz/en/latest/content/seismic/refraction/seismic_refraction_irregular_layers.html

How to create a link to a subsection

For the record, here is a problem I encountered while creating the physical properties chapter.
When possible, I create a link to existing material (example: Susceptibility.rst for Mag).
However in certain cases, physical properties were described in a subsection (example: dielectric permittivity in the GPR concepts document GPR_concepts_and_examples.rst). In these case I have not been able to create a link up to these subsection neither creating a reference (:ref:) that appear in the first level of the toctree. My only options have been to copy-paste the section of interest in a new .rst file.

If anybody has already encounter the problem and has a better, more elegant solution, it would be appreciated.

Thanks.

Dipole direction

I was pretty sure that the dipole moment extends from the negative(south) pole to the positive(north) pole. The text at the end of the

file:///C:/Users/micmitch/Documents/UBC/GIF/GPG/_build/html/content/magnetics/magnetics_extended_bodies.html#approximating-targets-using-magnetic-charges

section states that "The direction of the dipole goes from the positive to negative charge"

Just like to confirm that this is wrong before I change it.

Duplication of contents for physical properties section

Lists of duplicates content in the physical properties folder:
pages:
-magnetics_susceptibility_duplicate.rst
-seismic_velocity_duplicate.rst
-induced_polarization_physical_properties_duplicate.rst
-susceptibility_duplicate.html

    Pages have been duplicates due to a problem with the navbar on the website. The students were sent to the original page and so were leaving the "foundations" chapter. This solution is meant to be temporary until a more suitable one have been found.    

all duplicates images have been stored in ./images/images_duplicates/. This choice has been made to ensure that any displacement of the physical properties section would not require (as it happened before) to relocate all images links.

function to move all contents of image folders

to ensure all images are moved over each time, can we include a script that just grabs all of the contents of every folder labelled "images"?

Magnetic Surveying on GPG: Basic Principles (more material)

In the section Basic Principles we should have extra material to mesh with items provided later.

1. For the "Source" we need to introduce the topic of time variations and the magnitude and time scales over which the changes occur. That material will be used as a base for the Processing section.
2. Need a section on Remanent Magnetism. (some combination of the slides, existing material in GPG, and the App are required.
3. Modelling magnetic fields of uniform bodies of simple shape
   I think much of the material needed exists in the GPG.

add formula for seismic resolution

http://gpg.geosci.xyz/en/latest/content/seismic/reflection/seismic_reflection_vertical_resolution.html

(add formula to this page)

remove Poles and Stuff .tex

Is everything from the .tex now in the gpg?

CSS Browser Reset

firefox, chrome and explorer are rendering a few pages differently, messing with figure sizes. Can we include a call to a css browser reset in conf.py to fix this?

susceptibility.html - bar magnet

see DWO comment on line 29 of magnetic_susceptilibity.rst

• remove m from last line in box (wrong units)
• Substitute a magnetic fields from a bar magnet on the body (@dougoldenburg: superimpose a bar magnet on the last image?)

Move Physical Properties under Foundations?

Should we put physical properties under the Foundations? After seven steps and before survey methods?

put Travis-ci and testing on the repo

A couple approaches here: https://coderwall.com/p/wws2uq/have-travis-ci-test-your-sphinx-docs, https://github.com/opsschool/curriculum/blob/master/.travis.yml

Place holders for applets

Hi all:

There are placeholders for applets and the like. I use comment tags with <> in the appropriate sections.

Best,

Phil

Chapter on foundations and physical properties

The links for stepping through images and small movies don't work for me.

thibaut was preparing a section of physical properties. Is any of that hooked up?

Processing Magnetic Maps: Can benefit from further development

The following section

http://gpg.geosci.xyz/en/latest/content/magnetics/magnetics_plotting_processing.html#processing-magnetic-maps

has been flagged to indicate that it could benefit from additional development and figures.

Magnetic Surveying on GPG: Data

In this section we present a summary about the different types of magnetic data. (maybe with a screen shot of a body and the associated field)

1. Total field data
2. Total field anomaly
3. Magnetic field data
4. Magnetic field anomaly data
5. (eventually: magnetic field in a borehole and issues wrt orientation)

Magnetic Surveying on GPG: Interpretation

Comment: The flow outlined in the slides is good.

1. Inferences from data maps
   Comparison of processed data with geology sections
2. Interpret with a simple body and uniform magnetization (requires a parametric inversion)
   vertical pipe act like a pole source (generate magnetic field from a vertical pipe, carry through the analysis to get the depth of the pipe) This will serve as a template for the lab.
   compact object acts like a dipole (UXO) (a small block in a halfspace and invert to get orientation, magnitude and location)
3. Inversion (generally 3D but sometimes 2D)
   Minimal amount of text about inversion
   Example of synthetic inversion (say a block in a half-space)
4. Applications
   geology map
   vertical pipe from TBL
   dipole (UXO)
   3D inversion (Raglan)

Magnetics

• Create add cover image using TBL-like
• Move current content to new structure (see Gdoc)
• Add material in Processing
• Add material in Interpretation

Conductivity axis in physical properties

Conductivity axis needs to be labelled as mS/m

Phys Props: Permittivity

• Permittivity is defined as a frequency-dependent, complex valued parameter. However, the relative permeabilities for materials are given as a single, real-valued number. This makes our understanding of the physical property and its typical values extremely confusing. Need to resolve

Magnetic Surveying on GPG: Introduction

As a first pass to restructuring this, I suggest the following:

(a) Motivational examples.
(we can use the three in the slides: geologic mapping, inversion for a mineral deposit, UXO)

(b) Slide 14 from lectures.. (this is a generic slide used for all of our surveys; but here we explicitly have magnetic susceptibility as the physical property.

(c) Statement as to what magnetic surveying is. Replace the current text with the summary paragraph in Foundations/Surveys/Magnetics. That is much better than what is currently written.

(d) Keep the annotated figures that are currently in the Introduction. They are a nice visual summary about the basic method and also they tie in with Slide 14.

Absolute value around Hs/Hp

http://gpg.geosci.xyz/en/latest/content/electromagnetics/dual_loop_systems.html

• Remove absolute values around Hs/Hp
• Need to remove \sigma in right-hand-side of equation

@dougoldenburg

Pseudo-Section plots for DC app

Looks as though there might be a slight shift in the way the pseudo-sections are plotted since the midpoint of the pant leg anomaly is shifted ~3m to the left of the true along line location of the cylinder.

Figure Captions

• last figure in magnetics_earths_field
• magnetics_buried_dipole
• magnetics_extended_bodies

Typo in apparent conductivity?

In the formula for apparent conductivity, the second term should be \sigma_2 * \phi_v, not \phi_h?

(http://gpg.geosci.xyz/en/latest/content/electromagnetics/electromagnetics_fk_domain_systems.html#multilayer-earth-structures)

References need to be cleaned up

here: http://gpg.geosci.xyz/en/latest/content/magnetics/magnetics_susceptibility.html#references-cited-on-this-page

Half-width formulas for mag

We should add the half width formulas, and an explanation, for a monopole and dipole anomalies! (So we can search for it every time we need to remind ourselves :) )

Incomplete sentence?

http://gpg.geosci.xyz/en/latest/content/seismic/reflection/seismic_reflection_seismogram.html

Part of the sentence seems to miss, or brackets are unnecessary:

"Compute the acoustic impedance as a function of depth. In practice, (combine density and velocity logs to do this.)"

Figure attributions

We need to clean up figure attributions: https://wiki.creativecommons.org/wiki/Best_practices_for_attribution

Wherever possible: Title, Author, Source, License of the original image should be included in the figure caption

Radio button widget needs formatting: simple_vs_complex.html

The order of the buttons / layout is odd:

http://gpg.geosci.xyz/en/latest/content/magnetics/magnetics_complex_structures.html

Magnetic Dipole section, Figure 1

Concerning the first figure under the following section:

http://gpg.geosci.xyz/en/latest/content/magnetics/magnetics_buried_dipole.html#fields-due-to-a-magnetic-dipole

Do we want to define \Delta B and discuss the difference between \Delta B and B_t?

This could be done above the figure or in the missing figure caption.

Physical Properties - Mag

From @dougoldenburg in 306447e

"I've replaced some of the material from the gpg that was omitted. I think the interactive graphic display is effective and we should keep it. The susceptibility graph that you made is informative but so too is the plot that was omitted (adapted from Clark and Emerson). Although there is overlap of certain items, there is some additional information. Let's put both in for now. There is an inconsistency about hematite on the two plots.
For magnetic properties of soils some of the statements in the old gpg are relevant and maybe should be included some where. Also, the magnetic susceptibility of rocks often depends upon the % of magnetite. More information about this might be included.

@dougoldenburg : could you break this into a few todo's on specific pages?

Embed "sidebar" html widgets in gpg

http://gpg.geosci.xyz/en/latest/content/magnetics/magnetics_plotting_processing.html#processing-magnetic-maps

There are two sidebar html & javascript widgets that need to be transferred to small raw html files so that they can be directly embedded in the gpg

Variability of Earth’s field: Confusion with final Figures

In the second to last paragraph of the section below:

http://gpg.geosci.xyz/en/latest/content/magnetics/magnetics_earths_field.html#variability-of-earth-s-field

we state that "Three figures are given in a sidebar showing examples of different types of magnetic noise that may be encountered at time scales of several days, hours, and minutes."

There are only 2 figures provided and there is no explanation accompanying them. I honestly don't know what the 2nd figure which is labeled pipe-to-soil potential is showing us.

We either need a description of this figure or we should rework and delete some of this material.

Variability of Earth’s field: Confusion with final Figures

In the second to last paragraph of the section below:

http://gpg.geosci.xyz/en/latest/content/magnetics/magnetics_earths_field.html#variability-of-earth-s-field

we state that "Three figures are given in a sidebar showing examples of different types of magnetic noise that may be encountered at time scales of several days, hours, and minutes."

There are only 2 figures provided and there is no explanation accompanying them. I honestly don't know what the 2nd figure which is labeled pipe-to-soil potential is showing us.

We either need a description of this figure or we should rework and delete some of this material.

Diagrams for magnetics_extended_bodies

See DWO comment line 25 of magnetics_extended_bodies.rst (on Doug's branch)

Images for time variation of the magnetic fields

For the section on the Earth's magnetic field: http://gpg.geosci.xyz/en/latest/content/magnetics/magnetics_earths_field.html#variability-of-earth-s-field

see DWO comment in magnetics/magnetics_earths_field.rst (line 94)

Magnetic Surveying on GPG:

1. Basic Principles of Survey Design
   area of data acquisition must be large enough to capture the anomaly
   sampling interval must be sufficiently fine (for a dipole at least 3 points per half-width
   relationship between halfwidth and depth of burial for a dipole

Use Applet examples and buried prism to get these points across. In addition we could put together a list of some specific things they could do with the app to gain insight.

In general, we want to use a numerical modelling package to simulate the expected response and use that to help determine sampling strategy.
Again, we can provide a list of things they might explore (sheets, elongated bodies, small object at depth etc.);

1. Instrumentation (some background in GPG is good)
   Options: total field magnetometers (proton precesson, Cesium vapor)
   magnetometers (fluxgate)
   ganged systems like that for UXO
   borehole magnetometers
2. Field acquisition:
   Generally collect data in lines (particularly airborne data)
   On ground line spacing is ideally same as station spacing
   Need a base-station

Comment: Instrumentation could come first but from the viewpoint of understanding the survey, and the fact that we are following from Basic Physics, having it in #2 position works

phys props intro tables

something along the lines of http://em.geosci.xyz/content/maxwell1_fundamentals/formative_laws/ampere_maxwell.html#units

Magnetic Surveying on GPG: Magnetic susceptiblity

Almost all of the material needed here is in the new Phys Prop section. I think we just need a paragraph plus links to relevant components in the Phys prop.
Possible links: definition, units, lab measurements, tables etc.

search

the search doesn't work for content... is there an extension we can use?

Phys Props Susceptibility

Re-organization of materials should be considered. Final format can be used for other physical properties sections. Specific items:

1. Start with a sentence relating the physical property to a survey method. Then provide the definition of susceptibility right afterwards.
2. Where to put glossary of terms
3. Consider how much detail is required to explain magnetization in this section

Phys Props: Seismic (velocity tables)

• Needs table which distinctly shows vp and vs velocities for different rocks

Organization of Foundations unit

i) begin with the material for Seeing Underground and put all sections under that heading as in the old GPG.
ii) Next section: Seven-step method (don’t need a separate section for summary of seven step method)
iii) Survey methods
iv) Physical properties
v) Other items (title name) This includes (a) model types, (b) Inversion outline)

Uniform organization across each method

For each method:

• intro: why? (hooks, why is this interesting, thematic case history)
• physical properties (where can this be diagnostic)
• Basic principles (demonstrate what is happening… how: physics)
• Survey (field acquisition: sources, receivers)
• Data
• Processing
• interpretation
• examples
• (advanced)

DC Resistivtiy section needs some love

http://gpg.geosci.xyz/en/latest/content/DC_resistivity/index.html

General issues:

• Multiple figure labels (Looks like figure numbers were hard wired at some point)
• Inconsistencies in the when discussing the geometric factor. Define it one was in the text, but then as it is presented as the inverse of that in the figure. (http://gpg.geosci.xyz/en/latest/content/DC_resistivity/DC_measurements_and_data.html#measurements-potential-difference)

GPG Foundations

I've made alterations (and 2-Commits) for introductory paragraphs. The main item is to put Physical Properties into it's own section. The remainder of the text in Foundations is fine for now.
My next step will be to go through Physical Properties.

sign problem in FEM

It seems there is an error in the GPG FEM chapter (but also in all kind of material: slides...) for the sign of the phase-shift.
We wrote Hs_cos(wt+phi) with phi = pi/2 + tan^(-1)(wL/R) where it should be, with the same phi deifinition: Hs_cos(wt-phi)

a few todo's for seismic refraction

• can we make toys for body and surface waves? (fundamental physics part of seismic refraction)
• also: for waves and rays (in seismic refraction / waves and rays), we can put some of the animations @sgkang has made!?

Magnetic Surveying on GPG: Basic Principles

The basic thread for magnetic surveying is Slide 22 (sorry, I can't seem to get monosnap to copy the image here). Maybe this works.

Source: Earth's field (slides 15 to 20; or equivalent) + material in the current GPG (There is some good material in the GPG but it is very disorganized compared to what we want for our current structure.)
Main items
going from dynamo to earth's field as it interacts with solar wind
Earth's field at the surface, H,D,I; some maps; IGRF

Magnetizing the rocks
Magnetization or rocks (possibly links to Phys Prop section)
Dipole moment (volume integrated magnetization)
Introduce the app here

Fields
Anomalous fields are vectors
Measure components (projection onto a particular direction; x,y,z or earth's field
App examples (how same body buried at different locations in the earth yields different signatures)

   Things get more complicated because the anomalous field we are trying to measure is buried in the earth's field.  
   Subtract the IGRF
   Interpreting the result (particularly TMI and showing that it is project of the anomalous field onto the earth's field.

??? on looking at this we may choose to re-write the basic slide slightly. For now, combining the flow of the slides and the existing material on the GPG into the above framework takes us a lot closer to an end goal.