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sstaurus
20th Apr 2006, 19:53
Not sure if this is the right forum, but I'm a newb and this is training related.

Reading in my textbooks, I found out that all GPS/Satellite Navigation is in deg True. Even though currently most charts are in Magnetic, it says eventually Magnetic will likely be eliminated as all air-navigation slowly switches over to satellite navigation/GPS.

Is this true? Is radio-navigation going to eventually go away? And GPS will be it?

Is the trusty ol' compass due to be retired? I was kinda sad reading that, thinking I won't get as much use out of all the radio and chart reading I'm learning about.

Anyway, thanks for any comments!

itsbrokenagain
20th Apr 2006, 20:17
You need to keep reading thru the books some more, you will find far too many things need degrees magnetic, the list is way way way too long to even consider discussing it ( but dont worry someone here will! )

MIKECR
20th Apr 2006, 22:22
Just wait till the 'magnetic flip' occurs, that should put a spanner in the works! Apparently its overdue too.

Jinkster
20th Apr 2006, 23:04
Possible the compass could retire in some places

comment deleted following concern expressed by another poster .. related to the other deletions
:rolleyes:

rhovsquared
21st Apr 2006, 00:39
I hope to hell not, because then I can't set the gyrocompass and
I'd get lost:ouch:

arismount
21st Apr 2006, 00:53
.. your post really didn't add much to the discussion, my friend ..

Gnirren
21st Apr 2006, 01:40
.. no point leaving the responses to the earlier ill-considered post ..

Capt Claret
21st Apr 2006, 01:44
.. no point leaving the responses to the earlier ill-considered post ..

FlyVMO
21st Apr 2006, 01:47
.. no point leaving the responses to the earlier ill-considered post ..

regor
21st Apr 2006, 01:49
Can anyone clear up a specific enquiry about the mag' var' for EGGW.
The current mag' var' is 2 degrees West, with true rwy headings of 074 & 274.
So why do the latest Jeppesen charts show the magnetic rwy headings as 077 & 257?:hmm:

stilton
21st Apr 2006, 01:50
.. no point leaving the responses to the earlier ill-considered post ..

BGQ
21st Apr 2006, 04:23
.. no point leaving the responses to the earlier ill-considered post ..

Loose rivets
21st Apr 2006, 04:47
a couple of comments deleted following another poster's registering concern about them ... related to the earlier deletions

Now, back to an interesting question.

The magnetic pole, being a moveable feast, was something that was a gift to early navigators. Early being up until...about now. Of course we need to be independent of any single electronic system. We were going that way with INS, but the computer power was not really up to the mark then.

Now, we have the ability to measure light in a closed system, down to molecular levels, and we can certainly sum the output of such systems. The relativistic algorithms woven into the sat-nav signals, are proof of our mastery of this science. We know where we are in our orbit round our sun, almost down to the last perturbational tremor.

With what we have now, we are ready to navigate by such enclosed internal and quite independent systems...it really is time that we weaned ourselves away from electronically fragile orbiting clocks, let alone the wandering boiling mass in the centre of our planet.

Farmer 1
21st Apr 2006, 08:06
Can anyone clear up a specific enquiry about the mag' var' for EGGW.
The current mag' var' is 2 degrees West, with true rwy headings of 074 & 274.

That's a hell of a bend.

Rainboe
21st Apr 2006, 08:16
Whatever happened to this thread? Sort of went a bit screwy for some reason!

Before your degrees magnetic get made redundant, I think they will get metricated first. Stuff this 90 degrees to a right angle! For a start 'right' is unfair to angles that may be challenged by being a bit 'wrong', and 90 degrees, so in the cause of equality it will henceforth be known as a 'lesser wrong' angle. And there'll be 100 degrees in 'em instead of 90. Then we'll get rid of magnetic altogether, but probably before then, a meteor or bird flu or volcano or magnetic field flip disrupting the Gulf Stream will get us all and there'll be nobody to receive all those signals from Galileo or GS sats.

If you think this is stupid, it makes as much sense as some of the comments in this thread!

bookworm
21st Apr 2006, 08:41
Reading in my textbooks, I found out that all GPS/Satellite Navigation is in deg True. Even though currently most charts are in Magnetic, it says eventually Magnetic will likely be eliminated as all air-navigation slowly switches over to satellite navigation/GPS.

I think you (or possibly the textbook's authors) are missing the point. In the sat-nav future, once you have a system that tells you where you are and knows where you need to be, the arbitrary zero reference of your direction measure is irrelevant. An autopilot will fly from A to B just as well on magnetic or true, measured in degrees, grades or radians. The concept of flying a particular published track or heading loses its relevance, because you're always flying to an endpoint, regardless of the direction that happens to be.

In the mean time, we might as well pick the easiest/cheapest possibility as the zero reference for purposes like ATC telling you which direction to point your aircraft. That easiest/cheapest possibility probably remains magnetic north.

Oktas8
21st Apr 2006, 09:55
100 to a slightly less wrong angle? Someone already invented it, and it's called gradians.

But if you're going to optimise the direction system for computers' benefit, I dare say you'd use radians. And there are 1.5707963267948966192313216916398 of those in a slightly less wrong angle, but your computer finds that a more convenient number than 100.

Pi divided by two if you're wondering... :confused:

Farmer 1
21st Apr 2006, 09:58
So, what is "Left hand down a bit," in gradians?

arismount
21st Apr 2006, 13:14
Time to learn. This post had nothing to do with technical questions. Next ill-considered post will earn a banning.

boogie-nicey
21st Apr 2006, 14:48
Aviation should be our uniting blood.
Take care ......:O

CashKing
21st Apr 2006, 15:18
The obvious place to start is with the fundamental assertion of the book Origin and Destiny of the Earth's Magnetic Field by Thomas G. Barnes, I.C.R. Technical Monograph No. 4, copyright July, 1973, by the Institute for Creation Research (http://www.icr.org/). Barnes earned an A.B. degree in physics from Hardin-Simmons College, that the Earth's magnetic field is exponentially decaying. If this turns out to be untrue, or unsupportable, then Barnes' entire thesis is immediately nullified. So the next most obvious thing to do at this point is to present the reader with the data. These data, which follow in my table 2, are taken from Barnes (pages 33 & 61). Barnes in turn credits the ESSA report of McDonald & Gunst [5 (http://www.talkorigins.org/faqs/magfields.html#r5)] as his source. I once saw a copy of that report, but am not able to find it now. I presume that Barnes can copy, and that the data are as given in [5 (http://www.talkorigins.org/faqs/magfields.html#r5)]. In any case, these are the data that Barnes presents in defence of his own thesis, so the enterprising reader can examine the data as they see fit, in order to gauge compliance with the exponential decay hypothesis. Multiple values for one year indicate separate determinations, reported in separate original references. Those references are given by Barnes, but I have omitted them here.
Table 2
Dipole Magnetic Moment Data
From Barnes Pages 33 & 61 Year Dipole Moment
( 1022 amp-meter2)1835 8.5581845 8.4881880 8.3631880 8.3361885 8.3471885 8.3751905 8.2911915 8.2251922 8.1651925 8.1491935 8.0881942.58.0091945 8.0651945 8.0101945 8.0661945 8.0901955 8.0351955 8.0671958.58.0381959 8.0861960 8.0531960 8.0371960 8.0251965 8.0131965 8.017Before we go any farther, the attentive reader should have already spotted at least one problem. This table does not show any experimental uncertainties associated with any of the data points. This is the manner in which Barnes presents the data, and nowhere in his book is the subject of experimental uncertainty mentioned at all. I have not seen the McDonald & Gunst paper in preparing this article, so I cannot say whether or not they presented the data without uncertainties as well, but if they did, then their own argument suffers from the omission just as Barnes' argument does here.
From these data Barnes has determined that the Earth's magnetic field is decaying exponentially. Throughout his book, whenever he mentions this exponential decay, he points the reader to section II-D, page 36 to view the justification. On that page of his book, he justifies the exponential decay conclusion as follows, the emphasis is mine. B0, as referred to by Barnes, is the equatorial magnetic field strength, which is included in his tables, but omitted from mine.
"When values of the magnetic moment, M, in table 1 are plotted against time, t, on semi-log coordinate paper, the points lie approximately on a straight line, as one would expect for an exponential decay of the Earth's magnetic moment. This is also true, of course, for a plot of B0 against t. We therefore assume that the decay is exponential and write ... "This, of course, is no justification at all. Barnes simply assumed that the decay was exponential. However, later in the book, at the beginning of section IV, page 52, Barnes makes a slightly more heroic attempt to justify the exponential decay theory as follows:
"All data were processed on a CDC3100 electronic computer. A least square exponential fit was employed to evaluate the time constant. As a separate check it was noted that the variability was smaller for this exponential fit than for a straight line fit, as one would expect from the exponential solutions obtained from Maxwell's equations."In these two passages we see the full and entire text of the justification for deriving an exponential decay from the tabulated data. Anyone reading this who has had experience with numerical approximations, data curve fitting, and etc. should be able to recognize at once that the argument is very poor. First, it should be obvious that one cannot perform an unweighted fit, completely ignoring any experimental uncertainties. The early data from the mid 1800's, which are derived from experimental methods that are far less accurate and precise than modern methods, necessarily have much larger uncertainties associated with them, and should be weighted accordingly in any attempt to fit the data to a curve. Second, Barnes' reference to the "variability" of the exponential versus straight line fit is highly ambiguous. Is "variability" supposed to mean "variance"? If the variance of the fit is greater than the experimental uncertainties, then the line and exponential cannot be distinguished, in fact, one from the other. And what does "smaller" mean? Was the difference in variance between the two fits (if that is what "variability" means) significant or not? These kinds of curve fitting exercises are fraught with peril, and relying on the difference in variance between fits, where it is obvious that in fact either an exponential or a straight line will produce a "good" fit, is an exceptionally unreliable procedure.
Even without a plot, just by looking at the data tabulated above, the reader should be able to see that the moment values since 1935 appear essentially flat around a value of about 8.047 +/- 0.029, while the data prior to 1935 show a clear downward trend. One could easily argue that two straight lines fit the data better than one, and even better than one exponential (this is an exercise that I have not undertaken, but the motivated reader is welcome to see if my intuition is trustworthy). That fact alone will easily explain why a single exponential will fit the data better than a single straight line, as the slight curve of the exponential can better approximate the kink in the data. These considerations make it extremely difficult to use the data alone as an a-priori justification for any particular curve fit over another. In fact, one could over interpret the data even to the extent of claiming that the field was in decay until about 1935, when it then stopped decaying.

arismount
21st Apr 2006, 15:26
Rapidly losing patience here.

boogie-nicey
21st Apr 2006, 15:56
Arismount,

I hear you dude and yes the point is taken. But this kind of comedy happens from time. Nevertheless the magnetic pole debate is quite interesting let's get back to that seeing as we're all happy buddies again :D

sstaurus
21st Apr 2006, 21:21
I think you (or possibly the textbook's authors) are missing the point. In the sat-nav future, once you have a system that tells you where you are and knows where you need to be, the arbitrary zero reference of your direction measure is irrelevant. An autopilot will fly from A to B just as well on magnetic or true, measured in degrees, grades or radians. The concept of flying a particular published track or heading loses its relevance, because you're always flying to an endpoint, regardless of the direction that happens to be.
In the mean time, we might as well pick the easiest/cheapest possibility as the zero reference for purposes like ATC telling you which direction to point your aircraft. That easiest/cheapest possibility probably remains magnetic north.

Thanks for the response, however I think this is a little above me still. Can GPS tell direction? or only location? And doesn't GPS only use True? In such case why would you need magnetic degrees anymore if every aircraft can accept sat-link communication? Sorry if I'm still missing the point here.

It would seem to me radio-nav won't have much use left either.

CashKing
22nd Apr 2006, 00:46
Calculation of new positional information, which is based on both GPS and dead reckoning data, then takes place in a so-called "Kalman filter." At this location, the evaluation and combination of these data occur, including the previous history. Because processed GPS data enter the Kalman filter, i.e. values calculated for longitude, latitude and direction, one speaks of a loosely controlled system. The calculation of GPS data also already occurred via a Kalman filter.
Besides this implementation of a loose system with feedback, other loose systems exist without feedback (the dead-reckoning signals are not calibrated), as well as tightly controlled systems with or without feedback. In tightly controlled systems, raw GPS data, i.e. pseudo-ranges and delta ranges, are processed into a single Kalman filter, instead of the GPS data being processed first by their own Kalman filter. Because the Kalman filter makes up the heart of the calculations, we should briefly explain the principles behind it......

A Linear Dynamical System is a partially observed stochastic process with linear dynamics and linear observations, both subject to Gaussian noise. It can be defined as follows, where X(t) is the hidden state at time t, and Y(t) is the observation. x(t+1) = F*x(t) + w(t), w ~ N(0, Q), x(0) ~ N(X(0), V(0)) y(t) = H*x(t) + v(t), v ~ N(0, R)The Kalman filter is an algorithm for performing filtering on this model, i.e., computing P(X(t) | Y(1), ..., Y(t)).
The Rauch-Tung-Striebel (RTS) algorithm performs fixed-interval offline smoothing, i.e., computing P(X(t) | Y(1), ..., Y(T)), for t <= T.
Here is a simple example. Consider a particle moving in the plane at constant velocity subject to random perturbations in its trajectory. The new position (x1, x2) is the old position plus the velocity (dx1, dx2) plus noise w.
[ x1(t) ] = [1 0 1 0] [ x1(t-1) ] + [ wx1 ][ x2(t) ] [0 1 0 1] [ x2(t-1) ] [ wx2 ][ dx1(t) ] [0 0 1 0] [ dx1(t-1) ] [ wdx1 ][ dx2(t) ] [0 0 0 1] [ dx2(t-1) ] [ wdx2 ]We assume we only observe the position of the particle.
[ y1(t) ] = [1 0 0 0] [ x1(t) ] + [ vx1 ][ y2(t) ] [0 1 0 0] [ x2(t) ] [ vx2 ] [ dx1(t) ] [ dx2(t) ]Suppose we start out at position (10,10) moving to the right with velocity (1,0). We sampled a random trajectory of length 15.
http://www.cs.ubc.ca/~murphyk/Software/Kalman/aima_filtered.jpg http://www.cs.ubc.ca/~murphyk/Software/Kalman/aima_smoothed.jpg The mean squared error of the filtered estimate is 4.9; for the smoothed estimate it is 3.2. Not only is the smoothed estimate better, but we know that it is better, as illustrated by the smaller uncertainty ellipses; this can help in e.g., data association problems. Note how the smoothed ellipses are larger at the ends, because these points have seen less data. Also, note how rapidly the filtered ellipses reach their steady-state (Ricatti) values.
Directional input from GPS become inaccurate at low speeds until it loses all meaning at a standstill. This is a fact that one must consider. Therefore below a certain speed, the directional information from the gyro should be taken more strongly into consideration; at standstill the directional information should not be recalculated. At the same time, the standstill state should be utilized to reset the gyro's open-circuit voltage. Especially in cities, where dead reckoning is deployed more often than in open space due to gaps between buildings or tunnels, stops at traffic signals can be used for this purpose. Deviations are thereby reduced.

FlyVMO
22nd Apr 2006, 01:53
:ooh:
Do the JAA know about this????

Seriously though, its actually inspiring to see things discussed in depth. Can anyone recommend a good (in depth) text on GPS? Using it is one thing, but it is nice to know whats actually going on in the equipment.

DBTL
22nd Apr 2006, 19:05
How do people feel about the EU's Galileo GPS program? It's being sold as a significant improvement, offering an unforeseen redundancy to the use of public satellite positioning systems, including aviation uses. A me-too or what?

Rivet gun
22nd Apr 2006, 20:05
Especially in cities, where dead reckoning is deployed more often than in open space due to gaps between buildings or tunnels, stops at traffic signals can be used for this purpose. Deviations are thereby reduced.

Hey, impressive stuff. Next time I'm flying through a tunnel or have to stop at a traffic light I'll remember my FMC is in DR mode.

Pasted text from a web site about car navigation systems notwithstanding, I expect that Kalman filter algorithms are used in FMCs when combining data from multiple sensors (gps, dme, irs etc.) to generate a composite FMC position. Not sure about the relevance to GPS per se?

As to the original question, GPS cannot provide heading. It can only provide track and then only when moving. An AHRS can provide true heading, so you really need combined GPS / AHRS to be independant of the earth's magnetism. When all aircraft can have a combined GPS / AHRS costing less than current instruments we may see a switch to true navigation.

CashKing
23rd Apr 2006, 10:22
The applications are endless. Kalman filtering has proved useful in navigational and guidance systems, radar tracking, sonar ranging, and satellite orbit determination, to name just a few areas. Anything that moves, if it's automated, is a candidate for a Kalman filter.