Talk:Near-surface geophysics

Merger proposal

I have found no literature supporting the definition of Geophysical survey and Geophysical imaging as separate subjects. It makes more sense to cover them as part of their applications. Merging with Exploration geophysics would also make sense, but I have created a new page, Near-surface geophysics, which is in increasingly wide use as the general term for applied geophysics and related applications. RockMagnetist (talk) 19:13, 19 September 2011 (UTC)

I think I've figured out what you want where now :) One question though, does Geophysical imaging only apply to near surface exploration stuff or is the term also used for deep earth modelling? Seems seismic tomography does or at least that's where I've seen the term used ... Vsmith (talk) 20:00, 19 September 2011 (UTC)

(after ec w/ MN below) And the (tens of meters) depth restriction on this page seems a bit off. Most mineral/petroleum exploration seems after deeper targets. Vsmith (talk) 20:15, 19 September 2011 (UTC)

I'm not sure how the standard type of geophysical surveys used in oil and gas exploration - seismic reflection, controlled source electromagnetics, aeromag and gravity could be considered 'Near-surface'. It makes more sense to me to split the content of geophysical survey into this article and Exploration geophysics. There will necessarily be a degree of duplication, but I don't see how that can be avoided. I quite agree that Geophysical imaging is not a separate subject. Mikenorton (talk) 20:05, 19 September 2011 (UTC)

You both make good points. Probably Exploration geophysics should not be considered a subset of Near-surface geophysics. Would it make sense to merge Geophysical survey into Near-surface geophysics and Exploration geophysics? RockMagnetist (talk) 20:46, 19 September 2011 (UTC)

That was the intent of my comment - some techniques are used for both shallow and deep investigations, others only at either shallow or deep (although ground penetrating radar is the only one that comes to mind as restricted solely to near-surface). Mikenorton (talk) 21:02, 19 September 2011 (UTC)

• Oppose merger. Geophysical survey and geophysical imaging are not limited to "near-surface" applications. --Orlady (talk) 18:39, 23 September 2011 (UTC)

It seems to me that "near surface" is not a really fundamental distinction when we are talking about geophysical survey applications. Many sensing technologies have been adapted to relatively shallow as well as relatively deep applications, and even what we consider shallow or deep is relative. In my own field - subsurface mapping of archaeological sites - two meters would be considered deep, while others talk about tens of meters as shallow. Interestingly, Mikenorton (in his post above) considers GPR to be the only method that might be considered "shallow," while in our application it is the most deeply effective method, with magnetometers, resistivity, etc. having a lesser depth of effective investigation. There are reasons for this that are very specific to the field. Also, generating imagery from survey data is an interpretive tool, rather than a fundamental characteristic dividing these related disciplines. As I see it, "geophysical survey" is a very general label encompassing applications in a very wide diversity of fields whose practitioners do not necessarily talk to each other, and I think that the "Geophysical survey" page would be a good place to develop an article encompassing this diversity of applications and making generalizations about technologies and methods. Applications, technologies, and methods could be treated in separate articles in greater detail. Tapatio (talk) 03:56, 26 September 2011 (UTC)

Thank you all for the comments. You have convinced me that the articles should not be merged, so I am removing the merge tags. RockMagnetist (talk) 14:47, 26 September 2011 (UTC)

How shallow is shallow?

Following up on the comments in the section about the possible merge, it's obvious that different fields used the term in different ways. To me anything that's used to look in detail at the top few hundred metres is 'shallow' - this compares with some of the data that I look at which reaches the moho, so 30 km+. Geotechnical investigations (which I also occasionally get involved in) look mainly in the tens of metres range (although sometimes considerably deeper) and apparently archaeological surveys are more in terms of metres to centimetres. Do we need to change the current lede? Mikenorton (talk) 16:03, 26 September 2011 (UTC)

For a definition of near-surface, I'm mainly taking my cue from the Slater et al. reference. The only other source I have is the external link, "Near Surface Geophysics: A Resource for all Things Geophysical" which quotes Butler (2006) as saying "However there are occasional investigations to depths of 300 meters or more" (whatever "occasional" means). I don't have access to the Butler source, which I think is actually the Butler (2005) reference I have in my reference section.RockMagnetist (talk) 16:38, 26 September 2011 (UTC)