Sagnac and the earth's orbit.

[Jack_]

This person has me thinking.

http://api.ning.com/files/Hark62hE1...dYyOu1ooXfqn0SxtL*iXC4F9NTsZXu-ADT/Apaper.pdf

He compares the earth's sagnac effect to the earth's orbit around the sun as a sagnac effect.

I do not agree with his conclusions.

I think his comparison is valid.

Sagnac has been validated with experiments as well as with the earth's rotation.

It does not show up in the earth's orbit with GPS or it would not work.


So if sagnac is valid for the rotations, why is it not valid by GPS for the earth's orbit which is a rotation.

 

[rpenner]

Xinwei Huang shows all the signs of being a physics crackpot.

http://www.physforum.com/index.php?showtopic=27576

The Sagnac effect works because there is no inertial frame where a rotating fiber optic gyroscope or ring laser gyroscope has the start and finish of light in the same position. Thus it detects non-inertial rotation which changes the light path total distance. Usually this is done with simple geometries. Recently experiments were done with optical fibers on pulleys and a transceiver on a conveyer belt to show that in such a changing geometry, you could distinguish the conveyer belt's motion and change of loop geometry with respect to an experiment at rest relative to the laboratory.

But Xinwei seems to believe that this means that Sagnac experiments are uniformly sensitive to absolute linear velocity, which is not the reported result. As such, fiber optic gyroscopes are sensitive to the rotation of the Earth about the Sun only if you put them in a frame where one side of the ring is always in the direction of the sun. Since this is hundreds of times less angular movement than the Earth's rotation, the framework will appear in the laboratory to be slowly turning to follow the sun and a very sensitive instrument is needed.

Xinwei seems to ignore all of this and the simple fact that such gyroscopes are useful for terrestrial navigation precisely because they are sensitive to only angular velocity, not linear velocity and certainly not sensitive to Earth's motion about the Sun when they are held fixed in the laboratory frame.

And the Earth turns at 15 degrees per hour, not 15 radians per hour. So it is obvious at a minimum that Xinwei is out of his depth.

 

[Pete]

Hi Jack,
What precisely do you expect to see in the GPS system as a result of the Sagnac effect, and why do you think this would make it not work?

 

[Jack_]

Xinwei Huang shows all the signs of being a physics crackpot.

http://www.physforum.com/index.php?showtopic=27576

The Sagnac effect works because there is no inertial frame where a rotating fiber optic gyroscope or ring laser gyroscope has the start and finish of light in the same position. Thus it detects non-inertial rotation which changes the light path total distance. Usually this is done with simple geometries. Recently experiments were done with optical fibers on pulleys and a transceiver on a conveyer belt to show that in such a changing geometry, you could distinguish the conveyer belt's motion and change of loop geometry with respect to an experiment at rest relative to the laboratory.

But Xinwei seems to believe that this means that Sagnac experiments are uniformly sensitive to absolute linear velocity, which is not the reported result. As such, fiber optic gyroscopes are sensitive to the rotation of the Earth about the Sun only if you put them in a frame where one side of the ring is always in the direction of the sun. Since this is hundreds of times less angular movement than the Earth's rotation, the framework will appear in the laboratory to be slowly turning to follow the sun and a very sensitive instrument is needed.

Xinwei seems to ignore all of this and the simple fact that such gyroscopes are useful for terrestrial navigation precisely because they are sensitive to only angular velocity, not linear velocity and certainly not sensitive to Earth's motion about the Sun when they are held fixed in the laboratory frame.

Well, this is a published experiment on linear sagnac.
http://web.stcloudstate.edu/ruwang/PRL93.pdf

Anyway, I really do not care about that.

Tell me why the earth's orbit is not sagnac. It does not show up in GPS but yet a sagnac device has all components rotating light the earth's orbit.

I cannot make sense of this.

 

[Jack_]

Hi Jack,
What precisely do you expect to see in the GPS system as a result of the Sagnac effect, and why do you think this would make it not work?

The earth's orbit is a rotational frame. We do not see sagnac with this rotational frame.

I believe sagnac is a valid result, but cannot understand why it is not seen with the orbit.

You know I hate asking for help, so I am being truthful.

I cannot make it work. It is not in GPS.

 

[Pete]

The earth's orbit is a rotational frame. We do not see sagnac with this rotational frame.

I believe sagnac is a valid result, but cannot understand why it is not seen with the orbit.

What exactly do you think we should we see that is not seen?

 

[Jack_]

What exactly do you think we should we see that is not seen?

We should have to adjust in GPS for the sagnac earth's orbit. We do not.

 

[Pete]

We should have to adjust in GPS for the sagnac earth's orbit. We do not.

What exactly should have to be adjusted, and by how much?

 

[Jack_]

What exactly should have to be adjusted, and by how much?

I am getting a GPS satellite would be off a distance of a max 78 feet due to Sagnac at the equator.

The handheld units average at least 4 satellite distances so some would be north south with zero sagnac.

Still, this is large error.

The handheld units do not calculate sagnac.

In other words, it appears as if the earth's rotation (sagnac) is not showing up in GPS either.

 

[Pete]

I am getting a GPS satellite would be off a distance of a max 78 feet due to Sagnac at the equator.

The handheld units average at least 4 satellite distances so some would be north south with zero sagnac.

What exactly are you calculating, Jack?
Are you calculating a Sagnac effect due to the Earth's orbit, the Earth's rotation, a GPS satellite's orbit, or some combination?
And how does it translate to a distance?

Still, this is large error.

The handheld units do not calculate sagnac.

What data does a GPS unit receive from each satellite, how is that data processed, and how precisely do you think that the Sagnac effect should alter that process?

 

[AlphaNumeric]

*sigh*

If Jack thinks his initial link is worth reading then he further demonstrates his naivety about how science is done. And particularly if he thinks people having used GPS satellites to test GR predictions, with all the various effects which should be included. Its homework level stuff to work out the time dilation effects due to their motion and height. Adding in additional iterations due to other effects and expansions in perturbation series is less pleasant but has been done many many times using computers.

The original use of the GPS network was military usage. If the US military wants to shove a cruise missile down the throat of a bunker they'll want it to be more accurate than "To within 78 feet". So for it to be of accurate practical use it must be better than that. Hell, I have a GPS enabled phone which comes with Google Maps. When I turn on the GPS locator it can give my position to within a few feet in seconds. It can tell me which side of the road I'm on. It measures my walking speed immediately, even when talking across a road or room. Demonstrable evidence literally in your hands which demonstrates its accuracy.

There are minor variations in its accuracy which are due to local variations in the Earth's crust I think. These mean you can't get more than about 2 feet of accuracy without high grade material or a lengthy period of measurement. Across the globe local GPS related transmitters will broadcast the additional information you need to get a highly accurate reading quicker, though it varies with the time of day due to positions of the Moon etc so it goes from allowing errors of 2 feet to a few inches over a 6 hour period. Given the increase in timing technology I am absolutely certain that within 10 years GPS location will allow you to be tracked immediately within a crowd of people. If not already. Make of that what you will.....

 

[Jack_]

What exactly are you calculating, Jack?
Are you calculating a Sagnac effect due to the Earth's orbit, the Earth's rotation, a GPS satellite's orbit, or some combination?
And how does it translate to a distance?


What data does a GPS unit receive from each satellite, how is that data processed, and how precisely do you think that the Sagnac effect should alter that process?

I am only now talking about the earth's rotation and sagnac.

Every 30 seconds, a satellite sends its time and position and some correction information.

Next, any relative motion between the satellite and the receiver is corrected by doppler effects and not timing effects.

So, the earth rotates at 1000 mph = .277 miles per second.

A satellite can easily be 10,000 miles from the receiver of more.

That takes light .054 seconds to hit the receiver.

Now, at the equator with an east-west satellite, that implies 0.277 * 0.054 = 0.014958 miles sagnac correction. I am excluding the geometry of the arc because of the short distance. That is 0.014958 * 5280 feet/mile = 78.97824 feet.

That is a large sagnac correction and is not calculated in the hand held units.

This correction is caused by the earth's rotation.

 

[Jack_]

*sigh*

If Jack thinks his initial link is worth reading then he further demonstrates his naivety about how science is done. And particularly if he thinks people having used GPS satellites to test GR predictions, with all the various effects which should be included. Its homework level stuff to work out the time dilation effects due to their motion and height. Adding in additional iterations due to other effects and expansions in perturbation series is less pleasant but has been done many many times using computers.

The original use of the GPS network was military usage. If the US military wants to shove a cruise missile down the throat of a bunker they'll want it to be more accurate than "To within 78 feet". So for it to be of accurate practical use it must be better than that. Hell, I have a GPS enabled phone which comes with Google Maps. When I turn on the GPS locator it can give my position to within a few feet in seconds. It can tell me which side of the road I'm on. It measures my walking speed immediately, even when talking across a road or room. Demonstrable evidence literally in your hands which demonstrates its accuracy.

There are minor variations in its accuracy which are due to local variations in the Earth's crust I think. These mean you can't get more than about 2 feet of accuracy without high grade material or a lengthy period of measurement. Across the globe local GPS related transmitters will broadcast the additional information you need to get a highly accurate reading quicker, though it varies with the time of day due to positions of the Moon etc so it goes from allowing errors of 2 feet to a few inches over a 6 hour period. Given the increase in timing technology I am absolutely certain that within 10 years GPS location will allow you to be tracked immediately within a crowd of people. If not already. Make of that what you will.....

We are doing math here.

Do you have any to offer?

The earth's rotaional sagnac correction is not included in the GPS calculations. Further, the earth's orbit is a sagnac governed operation. I am having trouble making all this work.

Finally, several tests from moving light sources of different natures all verify light cannot be speed injected in the direction of travel and this is consistent with Sagnac and inconsistent with Ritz's theory.

So, why is this not showing up in GPS?



In particular, when the time dilation and gravitational field terms are taken into consideration it verifies (Schlegel 1973) the Sagnac time shift (equation (1)) as a direction-dependent change of synchronization of such a clock slowly transported around the Earth when compared to a clock at rest on (the rotating) Earth; a clock circumnavigating the world in an eastwards (westwards) direction loses (gains, respectively) 207.4 ns from the Sagnac effect. This was rendered more precise by the work of Allan et al (1985) who used a set of GPS satellites, whose timing was consistent to 2 parts in 1015, to measure this Sagnac effect to an accuracy of 5 ns or 2% over the largest ring area yet achieved. Half of this error was attributable to the atomic clocks, and half to inaccuracies in the determination of the satellite ephemerides and other non-null time delays. The link between time delay and phase shift is proved in section 2.2, and an extension of this suggestion for the detection of gravitomagnetism is discussed in section 8.1.

http://www.physics.berkeley.edu/res.../LaserRingGyro/Steadman/StedmanReview1997.pdf

 

[AlphaNumeric]

We are doing math here.

Do you have any to offer?

I used it all up smacking you about in the 'twin paradox' thread. Why don't you post some maths in retort to what I said there? Its been a few weeks now...

I am having trouble making all this work.

Ah, and as we all know, science is limited to what you can do.

Finally, several tests from moving light sources of different natures all verify light cannot be speed injected in the direction of travel and this is consistent with Sagnac and inconsistent with Ritz's theory.

So, why is this not showing up in GPS?

Why don't you find me a paper published in a peer reviewed, reputable journal which confirms your claim that the GPS network is inconsistent with relativity.

And then explain how my hand held phone is more accurate than to 78 feet, despite you claiming otherwise.

 

[Jack_]

*sigh*

If Jack thinks his initial link is worth reading then he further demonstrates his naivety about how science is done. And particularly if he thinks people having used GPS satellites to test GR predictions, with all the various effects which should be included. Its homework level stuff to work out the time dilation effects due to their motion and height. Adding in additional iterations due to other effects and expansions in perturbation series is less pleasant but has been done many many times using computers.

The original use of the GPS network was military usage. If the US military wants to shove a cruise missile down the throat of a bunker they'll want it to be more accurate than "To within 78 feet". So for it to be of accurate practical use it must be better than that. Hell, I have a GPS enabled phone which comes with Google Maps. When I turn on the GPS locator it can give my position to within a few feet in seconds. It can tell me which side of the road I'm on. It measures my walking speed immediately, even when talking across a road or room. Demonstrable evidence literally in your hands which demonstrates its accuracy.

There are minor variations in its accuracy which are due to local variations in the Earth's crust I think. These mean you can't get more than about 2 feet of accuracy without high grade material or a lengthy period of measurement. Across the globe local GPS related transmitters will broadcast the additional information you need to get a highly accurate reading quicker, though it varies with the time of day due to positions of the Moon etc so it goes from allowing errors of 2 feet to a few inches over a 6 hour period. Given the increase in timing technology I am absolutely certain that within 10 years GPS location will allow you to be tracked immediately within a crowd of people. If not already. Make of that what you will.....

I only listed the link simply because it is that person's idea to think of the earth's orbit as sagnac and not mine though it seems reasonable to me.

I did not say the entire paper is science and I made it clear I do not agree with the person's conclusions.

Anyway, why is the earth's orbit not sagnac?

 

[Jack_]

I used it all up smacking you about in the 'twin paradox' thread. Why don't you post some maths in retort to what I said there? Its been a few weeks now...

Ah, and as we all know, science is limited to what you can do.

Why don't you find me a paper published in a peer reviewed, reputable journal which confirms your claim that the GPS network is inconsistent with relativity.

And then explain how my hand held phone is more accurate than to 78 feet, despite you claiming otherwise.

LOL.

First, I did not say 78 feet and made it clear. That is only at the equator and east-west.

At least 4 satellites are averaged so that number is only the max amount.

But, I would say 25 feet is a good average. That is a lot. That is sufficient to run a ship aground in some of the smaller harbors.

And, this is my point, why is it not showing up?

They account for the ionosphere corrections in the gps message that causes a 1-2 meter error.

So, why would they not account for Sagnac? And, why is the earth's orbit not Sagnac?

Originally Posted by AlphaNumeric
I used it all up smacking you about in the 'twin paradox' thread. Why don't you post some maths in retort to what I said there? Its been a few weeks now...

You are able to talk yourself into anything.

 

[Pete]

It does not show up in the earth's orbit with GPS or it would not work.

So if sagnac is valid for the rotations, why is it not valid by GPS for the earth's orbit which is a rotation.

I am only now talking about the earth's rotation and sagnac.

So... why have you changed from your initial post?

Next, any relative motion between the satellite and the receiver is corrected by doppler effects and not timing effects.

Do you have the details of the doppler corrections? Does it vary by manufacturer?

So, the earth rotates at 1000 mph = .277 miles per second.

A satellite can easily be 10,000 miles from the receiver of more.

That takes light .054 seconds to hit the receiver.

Now, at the equator with an east-west satellite, that implies 0.277 * 0.054 = 0.014958 miles sagnac correction. I am excluding the geometry of the arc because of the short distance. That is 0.014958 * 5280 feet/mile = 78.97824 feet.

Thanks.
Thinking it through for the case of a multi-satellite fix, I see that this factor will consistently result in a naive location slightly east of the true location, between 33 and 44 metres at the equator, and correspondingly less at lower latitudes. This would not make the GPS system "not work", because the effect is easily* calculated and corrected for.
(*At least, it looks easy for the simple case of a stationary receiver - corrections for additional motion of the receiver will get more complex than I can handle, but should also be negligible.)

That is a large sagnac correction...

I agree that a significant correction is indicated.

...and is not calculated in the hand held units.

Can you support that claim?

Finding detailed information on GPS receiver algorithms is difficult, but I managed to dig up a NIST technical note by Neil Ashby: GPS Receivers and Relativity, in which Ashby describes how the path delay (of the signal from the satellite) is corrected for the Sagnac effect. See equations 34 to 41.

 

[Jack_]

So... why have you changed from your initial post?


Do you have the details of the doppler corrections? Does it vary by manufacturer?


Thanks.
Thinking it through for the case of a multi-satellite fix, I see that this factor will consistently result in a naive location slightly east of the true location, between 33 and 44 metres at the equator, and correspondingly less at lower latitudes. This would not make the GPS system "not work", because the effect is easily* calculated and corrected for.
(*At least, it looks easy for the simple case of a stationary receiver - corrections for additional motion of the receiver will get more complex than I can handle, but should also be negligible.)


I agree that a significant correction is indicated.


Can you support that claim?

Finding detailed information on GPS receiver algorithms is difficult, but I managed to dig up a NIST technical note by Neil Ashby: GPS Receivers and Relativity, in which Ashby describes how the path delay (of the signal from the satellite) is corrected for the Sagnac effect. See equations 34 to 41.

Yes, I saw that it is included and I've read that before and just did before you posted it.

This is one of two I found that claimed otherwise.



There is another relativistic effect, which is not considered for normal position determinations by GPS. It is called Sagnac-Effect and is caused by the movement of the observer on the earth surface, who also moves with a velocity of up to 500 m/s (at the equator) due to the rotation of the globe. The influence of this effect is very small and complicate to calculate as it depends on the directions of the movement. Therefore it is only considered in special cases.

The errors of the GPS system are summarized in the following table. The individual values are no constant values, but are subject to variances. All numbers are approximative values.

Ionospheric effects ± 5 meters
Shifts in the satellite orbits ± 2.5 meter
Clock errors of the satellites' clocks ± 2 meter
Multipath effect ± 1 meter
Tropospheric effects ± 0.5 meter
Calculation- und rounding errors ± 1 meter
http://www.kowoma.de/en/gps/errors.htm

I am going to believe Ashby.

OK, that solves the earth's rotation and sagnac with GPS in my view and I feel better.

Now, back to the original OP, why is the earth's revolution not included in GPS? This is a sagnac operation with a 150,000,000 KM radius.

 

[Pete]

The GPS satellite clocks are synchronized in the WGS 84, a reference frame which is rotating once per day (ie it's an Earth-Centred-Earth-Fixed frame).

If they were synchronized in a Sun-Centred-Earth-Fixed reference frame, then the Earth's orbital motion would matter.

 

[AlphaNumeric]

You are able to talk yourself into anything.

Let me know when you've got to intellectual honesty and balls to submit your work to a journal and I'll give you a hand. Until then all my criticisms of your methodology and your results stand unretorted.