Talk:Free-air gravity anomaly

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Context for this article.[edit]

Interested users; I note the lack of context flag on this page and am willing to address this. I have practiced geophysics for my career and made numerous gravity surveys. My suggestions are to expand the lead a bit; add some explanations in the section of computation and add a section on significance using examples - like the FAA over a Mid-Ocean Ridge.

This is my suggested lead draft; In geophysics, the study of subsurface structure and composition of the earth’s crust and mantle can employ surveys using a gravimeter to measure the departure of observed gravity from a theoretical gravity to identify anomalies due to geologic features below the measurement locations. The computation of anomalies from observed measurements involves the application of corrections that define the resulting anomaly. The free-air gravity anomaly, often simply called the free-air anomaly, is the measured gravity anomaly after a free-air correction is applied to correct for the elevation at which a measurement is made. The gravitational attraction of earth below the measurement point and above a reference level is ignored and it is imagined that the observed gravity is measured in air, hence the name. The free-air correction adjusts measurements of gravity to what would have been measured at a reference level. For Earth, this reference level is commonly taken as the mean sea level.[1][2] Theoretical or the reference gravity value at a location is computed by representing the earth as an ellipsoid and computing the gravity on that surface using the International Gravity Formula.(ref.) BrucePL (talk) 20:46, 24 April 2021 (UTC)[reply]

@BrucePL: Thank you for your offer to help with this page. It's nice to see a professional geophysicist contributing to Wikipedia. I think your suggested lead does provide needed context, but is better suited to the body of the article because it doesn't satisfy some of the Manual of Style guidelines for the lead. For example, with rare exceptions, the subject in the title should be defined in the first sentence. Also, a lead should summarize the contents of the article, not cover new material. So I think your paragraph should be part of the body of the article, with suitable citations, and a somewhat simpler summary should be added to the lead. Also, some of the sentences are rather dense. I think it's desirable and realistic to write this part of the article so a high school student would understand it. Finally, I'm a little worried by the footnote markers ([1][2]). I generally see that when someone copies material from elsewhere. Please keep in mind that you can't copy work from elsewhere, even your own work, if it has any copyright restrictions. I hope all of this isn't too discouraging. I would love to see you contribute to this article. RockMagnetist(talk) 20:58, 26 April 2021 (UTC)[reply]

@RockMagnetist: Thanks for noticing my post and for your helpful comments. I will do some work on the lead as you suggest. I've incorporated some of what is now on the page, hence the footnotes. I'll address those too. I was reluctant to delete the existing lead in its entirety because I think that's bad manners! I've created a few articles mostly on marine G&G and Antarctica, but also BLPs for geoscientists, and in particular women geoscientists. My main skill set is paleomagnetism. Cheers! BrucePL (talk) 22:34, 26 April 2021 (UTC)[reply]

I think you can probably guess what my main skill set is! I wouldn't worry too much about manners when the article is this sketchy. No one has invested much time in it and much of it was written in 2010. And, in general, leads are more likely to be rewritten than any other part of an article. RockMagnetist(talk) 23:37, 26 April 2021 (UTC)[reply]

@RockMagnetist: I worked on this - advice welcome. If it's adequate maybe remove the context flag? BrucePL (talk) 21:44, 28 April 2021 (UTC)[reply]

Thanks, Bruce. I see you have already removed the tag, which is fine. I think the context is mostly there, but a little more is needed. First, it doesn't say why you would use a free-air anomaly instead of a Bouguer anomaly. Without a little discussion of isostasy, it surely doesn't make sense to ignore the rock above the reference level. Second, you're equating the geoid with a reference ellipsoid, which is only approximately correct. I also tried feeding some of your text into a readability calculator, and the result was "college graduate" and "very difficult to read". You might find Wikipedia:Make technical articles understandable useful. RockMagnetist(talk) 22:00, 29 April 2021 (UTC)[reply]

@RockMagnetist: I see the confusion - it's misusing the word "reference". I use it incorrectly when meaning two different things; a datum and sea level. The ellipsoid and geoid are of course not the same. I'll sort that out. I will mention isostasy up higher. Thanks.BrucePL (talk) 21:43, 30 April 2021 (UTC)[reply]