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GPS set for problems from the Sun

Discussion in 'Amateur Radio News' started by XU7ADQ, Feb 10, 2010.

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  1. XU7ADQ

    XU7ADQ Ham Member QRZ Page

    Researchers say the Sun is awakening after a period of low activity, which does not bode well for a world ever more dependent on satellite navigation.
    The Sun's irregular activity can wreak havoc with the weak sat-nav signals we use.
    The last time the Sun reached a peak in activity, satellite navigation was barely a consumer product.
    But the Sun is on its way to another solar maximum, which could generate large and unpredictable sat-nav errors.
    The satellite navigation concept is embodied currently by the US GPS system and Russia's Glonass network, with contenders to come in the form of Europe's Galileo constellation and China's Compass system.
    It depends on what is - at its root - a simple triangulation calculation.
    A fleet of satellites circling the Earth are constantly beaming a radio signal with two bits of exceptionally precise information: where exactly they are, and at exactly what time.
    A sat-nav receiver on Earth - or on a ship or plane - is equipped with a fairly precise clock and the means to collect signals from the satellites that happen to be in its line of sight.
    It then works out, based on how long it took those signals to arrive, how far it is from each of those satellites. Some simple geometry yields its position.
    • 1. Satellites advertise their exact position, and the precise time at which they are sending it
    • 2. The signal travels through the outer atmosphere, the ionosphere; its speed depends on how much the Sun's radiation and particle winds are affecting the ionosphere's composition
    • 3. A receiver on Earth determines how long the signals took to arrive from a number of satellites, calculating the position from the time differences


    But those signals are incredibly weak and, as researchers have only recently begun to learn, sensitive to the activity on the Sun.
    Solar flares - vast exhalations of magnetic energy from the Sun's surface - spray out radiation across the electromagnetic spectrum, from low-energy radio waves through to high-energy gamma-rays, along with bursts of high-energy particles toward the Earth.
    The radiation or waves that come from the Sun can make sat-nav receivers unable to pick out the weak signal from satellites from the solar flare's aftermath.
    There is little that current technology can do to mitigate this problem, with the exception of complex directional antennas used in military applications.
    Sat-nav receivers will be blinded for tens of minutes, probably a few times a year at the solar maximum.
    Charged up
    A further complication comes from the nature of the outermost layer of the Earth's atmosphere, the ionosphere.
    That is composed in part of particles that have ionised, or been ripped apart by radiation from the Sun, with the composition dependent on how much radiation is coming from the Sun at a given time.
    The problem comes about because sat-nav technology assumes that signals pass through at a constant speed - which in the ionosphere isn't necessarily the case.
    "The key point is how fast the signals actually travelled," said Cathryn Mitchell of the University of Bath.
    "When they come through the ionosphere, they slow down by an amount that is actually quite variable, and that adds an error into the system when you do the calculations for your position," Professor Mitchell told BBC News.
    The amount of solar activity runs on many cycles; the ionisation will be different on the sun-lit side of the Earth from the night side, and different between summer and winter; each of these cycles imparts a small error to a sat-nav's position.
    But the disruption caused by solar flares is significantly higher.
    The increased radiation will ionise more molecules, and the bursts of particles can become trapped in the ionosphere as the Earth's magnetic field drags them in.
    The effects that sat-nav users will face, however, are difficult to predict.
    "We can look at the measurements from the last solar maximum," Professor Mitchell said.
    "If we project those forward, it varies quite a lot across the Earth; looking at the UK it will be about 10-metre errors in the positioning."
    The errors would be much more long-lasting than the "blindness" problem, lasting hours or even days.
    "Ten metres out is probably going to be OK for a sat-nav system in a car, but if you're using the system for something safety-critical like ships coming into harbour for navigation or possibly in the future landing aircraft, you're looking for much greater accuracy and more importantly, much greater reliability."
    Bob Cockshott, a director of the government-funded Digital Systems Knowledge Transfer Network, said that for most consumer applications such as sat-nav for cars, the problem will be more troublesome than dangerous.
    "You might find for a number of hours or even a day or two you couldn't go out surveying or be able to dock your oil tanker at the deep-ocean oil well," he told BBC News.
    "It's more at the annoyance level than something that's going to bankrupt your business."
    A number of schemes have been proposed to do real-time corrections to the signals as the atmosphere changes, allowing for local adjustments that are broadcast to receivers by other means such as the mobile phone network.
    However, Mr Cockshott said that it remains unclear whether such a correction makes sense economically for manufacturers of sat-nav-enabled technology.
    So as the Sun builds up to its crescendo in a few years' time, be aware that your sat-nav may for a time give some strange results - or for a short while none at all.
     
  2. K5CO

    K5CO Ham Member QRZ Page

    here comes the sun

    Little darlin', it's been a long cold lonely winter,
    here comes the sun......
     
  3. KL7AJ

    KL7AJ Premium Subscriber QRZ Page

    See my recent post: How to not get lost. :)

    eric
     
  4. K8ERV

    K8ERV QRZ Member QRZ Page

    Sounds like a good idea.

    TOM K8ERV Montrose Colo
     
  5. N5TGL

    N5TGL Ham Member QRZ Page

    That's ok, because we have LORAN-C as a backu.....oh wait.
     
  6. NA0AA

    NA0AA Ham Member QRZ Page

    Dang it, you beat me to it.

    This just in: Satellites are vulnerable to solar conditions, photos at 11.
     
  7. W5DQ

    W5DQ Guest

    A GPS unit is a device that tells you, with great precision, EXACTLY where you are lost.
     
  8. G0GQK

    G0GQK Ham Member QRZ Page

    Reading comments from a knowledgeable user somewhere else, it seems that this is another of the "could be" press releases, eg. a 7.5 tsunami "could" hit islands in the Pacific in the next 2000 years.

    G0GQK
     
  9. KB0MNM

    KB0MNM Ham Member QRZ Page

    Solar changes fact, DGPS known remedy

    :rolleyes:
    Unlike the millenium bug scare, it has always been a known fact that solar activity can and does interrupt conventional GPS time of propagation as well as conventional communications at lower frequencies. The european constellation WAAS satellites are in the same category in terms of propagation delay variance. For terrestrial ( ground ) navigation, there are a number of Differential Global Positioning System ( DGPS ) transceivers
    which apply a correction signal only to GPS systems which have the
    specialized receivers needed. In addition, laser-ring-gyroscopes are used in some mobile systems. Please read about these systems before you
    dismiss the importance of accurate navigation. Some folks cannot afford to be wrong, ie. historically, fishing rights are often contested.
    73 de KB0MNM- Jon in the (north continent) United States of America:)
     
  10. KA1XC

    KA1XC Ham Member QRZ Page

    I don't think a few tens of meters of innacuracy would be a big deal to most commercial users of GPS, as long as they know it could happen.

    When GPS was first deployed it's accuracy was intentionally degraded for non- U.S./NATO military users of the system so that it could not be used as an ultra-accurate weapons targeting system by non-friendlies. It wasn't until a few years ago that the USAF enabled the high accuracy mode for all users, and if they wanted to they could turn it back off at any time.

    John
     
  11. K8ERV

    K8ERV QRZ Member QRZ Page

    Unless you are trying to dock a boat in a fog. Ouch----

    TOM K8ERV Montrose Colo
     
  12. NA0AA

    NA0AA Ham Member QRZ Page


    What you say was true...before the precision GPS approaches that the aircraft now use. a 50 meter error on an approach could put you off the runway, no problem at all.

    Next thing to go: VOR's, NDB's and the ILS. THAT will make life interesting.

    Sadly, it would only take a handful of inexpensive launch vehicles to disable a large percentage of the GPS constallation, OR a couple of properly equipped aircraft to deny GPS data to a large area of the planet at any time.

    It's really not that robust a system when you get right down to it.
     
  13. W5BFE

    W5BFE Ham Member QRZ Page

    Good thing we just got rid of LORAN! :D
     
  14. VK3HJ

    VK3HJ Premium Subscriber QRZ Page

    Navigation skills, not gadgets

    Loss of GPS will not affect my ability to navigate using a paper map!
    As a "modern" society, we've allowed ourselves to become dependent on many conveniences and comforts. Just listen to the city people scream when the electricity supply is interrupted! We have severe thunderstorms again this afternoon, and I am expecting the power to go off any minute...........
    Well, not this minute! I have battery backup for my radio to work C21DL when he goes to 10m.
    When the GPS is affected, we'll find out who didn't learn navigation!
    Luke VK3HJ
     
  15. K8ERV

    K8ERV QRZ Member QRZ Page

    If GPS gets knocked out I won't be able to find the yard sales. Bummer!

    TOM K8ERV Montrose Colo
     
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