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Offline stack

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Re: Paper. Simply irrefutable.
« Reply #20 on: January 29, 2019, 08:17:28 AM »
Quote
Some do. This one has a GPS receiver built in

So it automatically calculates the latitude correction then? I can only assume that you have conceded the discussion.

No, it does not. And I do not.

Re: Paper. Simply irrefutable.
« Reply #21 on: January 29, 2019, 10:33:06 AM »
There are three factors to consider (RE model assumed):

1) The earth is ellipsoidal, at the equator, an observer is further away from the centre of gravity than an observer at the poles, causing things to weigh less at the equator.

2) The earth rotates. The centrifugal force at the equator is therefore greater than at the poles causing things to weigh less at the equator.

3) The earth is an imperfect shape of varying density. It can be approximated by a perfect mathematical ellipsoid of uniform density. It is also a dynamic system, new islands are being created through geological processes, land is eroded by wind and tide and we have tides and tectonic shift. Consumer grade GPS devices work from a mathematical ellipsoid because it makes calculation (relatively) easy. Their typical accuracy of +/- a few metres means this is a good enough approximation for everyday use without the need for any further correction.

WGS84 for example uses a reference ellipsoid (a perfect mathematical shape), it also uses a geoid (EGM96), an irregular surface representing the earth's actual gravitational field, broadly speaking the shape the oceans would take if you took away all the land. It only differs from the reference ellipsoid by a relatively small amount (less than 100m anywhere on earth). The actual surface of the earth is different from both of these - Mount Everest for example.

If the earth were a perfect ellipsoid, then you could easily calculate gravity at any latitude, however it isn't so if you want high accuracy, you need to refer to the geoid in your calculations as well.

Just because the earth isn't a perfect shape doesn't make it flat.

(source image below - Wikipedia)


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Offline Tom Bishop

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Re: Paper. Simply irrefutable.
« Reply #22 on: January 29, 2019, 02:51:06 PM »
If the device was capable of capturing the latitude acceleration data then the corrections for latitude would not be necessary.

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Re: Paper. Simply irrefutable.
« Reply #23 on: January 29, 2019, 06:09:31 PM »
If the device was capable of capturing the latitude acceleration data then the corrections for latitude would not be necessary.

The device I referenced doesn't capture latitude acceleration data.

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Offline Tom Bishop

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Re: Paper. Simply irrefutable.
« Reply #24 on: January 29, 2019, 08:30:35 PM »
If the device was capable of capturing the latitude acceleration data then the corrections for latitude would not be necessary.

The device I referenced doesn't capture latitude acceleration data.

Yes, that's what our Gravimetery article says.

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Re: Paper. Simply irrefutable.
« Reply #25 on: January 29, 2019, 09:00:51 PM »
If the device was capable of capturing the latitude acceleration data then the corrections for latitude would not be necessary.

The device I referenced doesn't capture latitude acceleration data.

Yes, that's what our Gravimetery article says.

The device I referenced doesn't capture latitude acceleration data. It captures it's location via GPS but does not correct for latitude.

Offline JCM

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Re: Paper. Simply irrefutable.
« Reply #26 on: January 30, 2019, 08:45:15 PM »
Tom has seen the data for parts of Europe and Africa which measured gravity at hundreds of locations and it correlated perfectly with latitude so this is nothing new except the mapping of anomalies.

There is an expected gravity amount at every latitude, this is confirmable.  When local gravity is not what it is expected to be, this is useful information as it infers a regional effect is causing it more then just the geometric location on the planet. That is recorded as plus/minus the normal expected gravity reading.    This is the entire purpose of the studies to find the local anomalies and map them, not to preset gravity readings to confirm a globe to flat Earthers.

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Offline Tom Bishop

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Re: Paper. Simply irrefutable.
« Reply #27 on: January 30, 2019, 09:41:27 PM »
The papers on gravimeter surveying show that the corrections for latitude are artificial. What information do you have to contradict it?

Quote from: Wiki - Gravimetry
Corrections for Latitude

It is asserted that gravimetry has shown trends at different latitudes, and so this is validation of the idea that it is really measuring "gravity". We find that this assertion is unfounded.

From a university course on gravity surveying we read:

http://www.geol-amu.org/notes/m10-1-4.htm (Archive)

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  “ Recall that, if the Earth were an homogeneous ellipsoid, the value of gravity at the surface would be given by:

g = g0 (1 + k1 sin2 ϕ – k2 sin2 2ϕ)

The objective of gravity surveys is to look for deviations from this reference value. ”

If the objective of gravity surveys is merely to look for deviations from a round earth reference model with the vibrating gravity theory, then the final computed number in meters per second squared would becomes meaningless for the purpose of discussion. Any modifications to the reference values are constructed on an entirely theoretical basis.

The above page tells us that there is a theoretical model and that the goal of gravity surveys is to modify that model. Further down we see, among the list of corrections to be made, the latitude correction:

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  “ Latitude correction: The earth's poles are closer to the centre of the equator than is the equator. However, there is more mass under the equator and there is an opposing centrifugal acceleration at the equator. The net effect is that gravity is greater at the poles than the equator.

For values relative to a base station, gravity increases as you move north, so subtract 0.811 sin(2a) mGal/km as you move north from the base station. (where a is latitude). ”

We read that we are subtracting or adding values to the reference model and the data to make the corrections for latitude, which is very different than using the data to determine the latitude. The claim that the final number is meaningful as evidence to showcase any particular point is shown fallacious.

United Nations University

On p.9 of Seismic Activity, Gravity, and Magnetic Measurements (Archive) by LaGeo as part of the United Nations University Geothermal Training Program we read:

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  “ 3.6 Reduction of data

Gravimeters do not give direct measurements of gravity; rather, a meter reading is taken which is then multiplied by an instrumental calibration factor to produce a value of observed gravity (known as gobs). The correction process is known as gravity data reduction or reduction to the geoid. The various corrections that can be applied are the following. ”

The section goes on to list a number of corrections, including corrections for latitude and elevation, which is not data contained in the measurement readings:

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  “ Latitude correction (gn) - Correction subtracted from gobs that accounts for earth's elliptical shape and rotation. The gravity value that would be observed if the earth were a perfect (no geologic or topographic complexities) rotating ellipsoid is referred to as the normal gravity. ”

  “ Free-air corrected gravity (gfa) - The free-air correction accounts for gravity variations caused by elevation differences in the observation locations ”

These are artificial corrections which are added or subtracted to the data and reference model. If the earth were really elliptical or rotating, then these artificial corrections would not be necessary.

Re: Paper. Simply irrefutable.
« Reply #28 on: January 30, 2019, 09:49:52 PM »
One day we will read:  I contacted xxx and explained they were incorrect. They were very grateful and have redesigned their equipment.