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Free-air gravity anomaly measurements from Operation Icebridge aircraft are described in A fault-bounded palaeo-lake basin preserved beneath the Greenland Ice Sheet (open access).

Question: These appear to be at least smooth to 1 mGal if not less. Standard gravity is nearly one million Gal mGal, so these are part-per-million type acceleration measurements made inside an airplane. How does one do this? How are mGal-smooth free-air gravity anomaly measurements made exactly on a presumably bumpy airplane ride?

A heck of a lot of averaging or damping and GPS and/or lidar/radar reconstruction of average height?


Fig. 7. Gravity and magnetic anomalies... (b) Gravity anomaly modelling. The open circles mark free-air gravity anomaly measurements along the profile (the gap at ∼50 km reflects a turn in the flight line, where gravity data are unavailable), and the coloured lines denote the calculated gravity effect associated with the interfaces in our crustal model (panel c). The gravity effect of the topography contains a signal from both the ice surface and bed interfaces.

Fig. 7. Gravity and magnetic anomalies... from A fault-bounded palaeo-lake basin preserved beneath the Greenland Ice Sheet

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  • $\begingroup$ There may be additional/different tags that apply. $\endgroup$
    – uhoh
    Commented Nov 11, 2020 at 23:17
  • $\begingroup$ Query: are your mathematical factors correct? Milli is one thousandth, thus wouldn't 1 mGal be one part per thousand, not one part per million of 1 Gal? $\endgroup$
    – Fred
    Commented Nov 12, 2020 at 0:26
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    $\begingroup$ Much clearer than before $\endgroup$
    – Fred
    Commented Nov 12, 2020 at 0:41
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    $\begingroup$ The paper cites Tinto et al. (2019) as source of the gravity data: doi.org/10.5067/R1RQ6NRIJV89 The 'user guide' tab has some details about data acquisition and processing that might be worth reading (but are too technical for me). $\endgroup$ Commented Nov 12, 2020 at 9:41
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    $\begingroup$ @uhoh Glad you could make something out of this! :) $\endgroup$ Commented Nov 12, 2020 at 12:33

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