How to do this ?

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bushido
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How to do this ?

Post by bushido »

hello, i'm working with a potassium mag, i'm a beginner and trying to learn.
i read some books and i saw some black and white maps made out of magnetic anomalies maps (red and blue)
i would like to know how to go from the usual magnetic map to the result shown in the attached picture.
what's the best software that is used to process magnetic data for archeology ? and what's the best method used to determinate the depth of archeological feature using the mag map ?
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IMG_20230411_181710.jpg
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markg21ca
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Re: How to do this ?

Post by markg21ca »

Producing a shaded grey scale image in Geosoft is pretty straight forward: https://files.seequent.com/MySeequent/t ... tables.pdf.
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Re: How to do this ?

Post by markg21ca »

With regards to estimating the depth to the magnetic source, there is the old school half-width method (https://gpg.geosci.xyz/content/magnetic ... ation.html), there is 2D block modeling available as freeware (https://geoss.com.au/software.html#pdyke), and there are more rigorous 3D inversion programs like (https://www.researchgate.net/publicatio ... netic_data).
bushido
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Re: How to do this ?

Post by bushido »

thanks for the reply but producing a greyscale shaded image with anomalies converted to structures is not straightforward and it's not just painting. i have oasis montaj and I tried every possible option and didn't get close to the result on the picture.
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Re: How to do this ?

Post by kaminae »

I'm no an expert in potential field images interpretation. But shaded relief (gray-scale) image looks like a kind of transformation. There are many of them: high derivations/or their combination, analytic signals, linearments, or even one of component of PCA.
Sources depth - I recommend old fashioned rules based on anomalies sizes.
markg21ca
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Re: How to do this ?

Post by markg21ca »

The same image along with a scale bar showing the units (nT) can be seen on the author's web site (https://historicengland.org.uk/research ... echniques/) which indicates that derivatives were not applied, but the usual series of processing steps were taken.

This publication from the same author goes into detail about this type of survey and processing on another site (https://historicengland.org.uk/research ... August2019) that clearly indicates that the magnetic data is being presented with simple greyscale, most likely with a bid of shading as well.
bushido
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Re: How to do this ?

Post by bushido »

thank you everyone for help. after long hours of research and reading, i found that converting magnetic data to structures is a part of the interpretation process and can be done only by three software :
-Geoplot owned by geoscan research (paid)
-Terrasurveyor 64 ( paid and has 30 day trial mode)
-Snuffler (free)
Geoplot and Terrasurveyor are very advanced with many extra functions compared to snuffler and dedicated to archeology.
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Re: How to do this ?

Post by 99thpercentile »

How did you deploy your magnetometer? The reason I ask is that every archeological magnetometer that I am aware of is a fluxgate gradiometer. Most geophysical magnetometers are total field single sensors. The geophysical magnetometers can usually be deployed as a gradiometer if you have multiple sensors, or you can upward continue some data and subtract the data to create a pseudo gradient.

Here is a sample report the Neil LInford wrote about towed magnetometer arrays with results similar to what you want.
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Linford_et_al_2019.pdf
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Ryan E. North, PhD, RPG, GISP
Principal Geophysicist
ISC Geoscience
ryan.e.north@iscgeoscience.com
bushido
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Re: How to do this ?

Post by bushido »

99thpercentile wrote: Sun Apr 23, 2023 10:38 pm How did you deploy your magnetometer? The reason I ask is that every archeological magnetometer that I am aware of is a fluxgate gradiometer. Most geophysical magnetometers are total field single sensors. The geophysical magnetometers can usually be deployed as a gradiometer if you have multiple sensors, or you can upward continue some data and subtract the data to create a pseudo gradient.

Here is a sample report the Neil LInford wrote about towed magnetometer arrays with results similar to what you want.
We use Potassium gradiometer with sensors set vertically separated by 1 meter and we bought an overhauser sensor that we use as a base station for diurnal corrections.
ssheriff
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Re: How to do this ?

Post by ssheriff »

Another source of free software for what you want to do are the USGS Geosoft executables (they're excellent) by Phillips:
https://pubs.usgs.gov/of/2007/1355/pdf/of07-1355.pdf
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