Solar Flare

[+fizzymagic]

This story indicates that there was a large solar flare yesterday. Particles will likely be arriving over the next couple of days.

 

I'd enable WAAS if you usually leave it disabled.

[+TeamRJJO]

The WAAS carrier frequency is that same as that of the GPS signal, so if the flare disrupts GPS signals (which is unlikely, by the way), WAAS will be disrupted as well.

 

Peace,

TeamRJJO

[+Renegade Knight]

WAAS by design is intended to meausre the disruption and provde the differential correction to adjust for it. So long as the error isn't random (meaning you can't correct for it) WAAS would improve your GPSs accuracy. Perhaps not as much as normal, but more than without.

[+fizzymagic]

The WAAS carrier frequency is that same as that of the GPS signal, so if the flare disrupts GPS signals (which is unlikely, by the way), WAAS will be disrupted as well.

Huh?

 

The reason for using WAAS during solar storms is that WAAS provides near-real-time ionospheric delay corrections. The ionosphere changes significantly during solar storms, which means that a non-WAAS GPS unit can experience significant position errors.

 

UPDATE: I found a really cool page that has a downloadable movie of the ionospheric Total Electron Content (TEC) during a solar storm. (The TEC is what causes GPS position errors, because the signals propagate more slowly through high-TEC regions than through low-TEC regions).

Edited September 8, 2005 by fizzymagic

[+budd-rdc]

Thanks for the heads up Fizzy. I got two non-WAAS GPSr's, so maybe this is a good time to go to ADJUSTED benchmarks to observe the errors firsthand!

[+StarBrand]

See This site for current data on "Space storms".

 

Anything creating a storm of 3 or higher can have an impact on the sats. A storm of 5 would have a serious impact.

[+worldtraveler]

There was a lot of discussion here back when WAAS was newly available on handhelds. The consensus then, after a lot of field testing in typically tree-covered environments, was that more (though less precise) non-WAAS satellites in view usually yielded a greater positional accuracy than fewer WAAS satellites in view. That's why many of us turned WAAS off. Do any of you experts know if this disturbance is likely to significantly change the results in the field?

[+JohnnyVegas]

The ionosphere changes significantly during solar storms,

 

This is true, but the effect is more pronounced on the lower lower frequencies,

Bellow 50 megs. GPS signals are in the microwave region of the spectrum and the effect should not be all the noticable, as for me, I have always had WAAS turned on. I never bought into the junk science that turning it off would improve GPS reception.

Edited September 9, 2005 by JohnnyVegas

[WH]

The WAAS satellties are low on the horizon from here so unless I was standing in a wide open field, I wouldnt pick them up anyways.

[+fizzymagic]

This is true, but the effect is more pronounced on the lower lower frequencies,

Bellow 50 megs. GPS signals are in the microwave region of the spectrum and the effect should not be all the noticable...

The ionospheric TEC is the single largest source of GPS position uncertainty. The effect is quite noticeable indeed.

[+fizzymagic]

The WAAS satellties are low on the horizon from here so unless I was standing in a wide open field, I wouldnt pick them up anyways.

<sarcasm>

 

Really? I didn't know that people in MA couldn't get satellite TV! That's amazing!

 

</sarcasm>

 

Your post is nonsense. The WAAS satellites are not low on the horizon from your location. From Boston, for example, the AOR-W WAAS satellite is at an elevation of 38 degrees, which is hardly "low on the horizon." In fact, it's are a lot higher in the sky for you than either WAAS satellite is here in California, and I rarely have any trouble getting WAAS corrections. Maybe you need a better receiver.

 

Seriously. I find it puzzling that people from the Northeast seem to think the WAAS satellites are so hard to see. They aren't! Even from Bar Harbor, Maine, the elevation of AOR-W is almost 37 degrees. ALmost all of Europe is north of MA, and they don't have any trouble with EGNOS. If you were near the Arctic Circle, I could see having some trouble, but there is no problem seeing the WAAS satellites from anywhere in the continental US.

 

So please indulge my curiosity: where did you get the idea that the WAAS satellites are "low on the horizon" from your position?

 

(BTW: if anyone is interested in calculating these numbers for their position, there is a neat website that will do it. AOR-W, the WAAS satellite over the Western Atlantic, is on INMARSAT 3F4, at W 54 degrees, and POR, the WAAS satellite over the Pacific, is on INMARSAT 3F3, at E 178 degrees.)

Edited September 9, 2005 by fizzymagic

[+fizzymagic]

The consensus then, after a lot of field testing in typically tree-covered environments, was that more (though less precise) non-WAAS satellites in view usually yielded a greater positional accuracy than fewer WAAS satellites in view. That's why many of us turned WAAS off.

There is no such thing as a WAAS or non-WAAS satellite. The problem that led to this "consensus" was a seriously flawed WAAS implementation by Garmin. It had nothing to do with the WAAS system.

 

This particular piece of pseudoscience/urban legend has proven remarkably difficult to eradicate.

 

Unless you still own an old Garmin GPSr and have never updated the firmware, WAAS mode will always give you better positional accuracy than non-WAAS mode.

[robertlipe]

This particular piece of pseudoscience/urban legend has proven remarkably difficult to eradicate.

Yes, it definitely has. Every time I hear "WAAS drains batteries" or "it makes my unit run slowly" or "it makes me break out in hives" I just want to scream.

 

Use a unit that does WAAS and doesn't suck and these are non-problems. (Well, can't help with the hives thing...)

[+budd-rdc]

UPDATE: I found a really cool page that has a downloadable movie of the ionospheric Total Electron Content (TEC) during a solar storm. (The TEC is what causes GPS position errors, because the signals propagate more slowly through high-TEC regions than through low-TEC regions).

I checked out the movies.

 

Can I deduce that coordinates taken at night with non-WAAS GPSr's are likely to be better than those taken during the day?

[+fizzymagic]

Can I deduce that coordinates taken at night with non-WAAS GPSr's are likely to be better than those taken during the day?

Yes. They are. That's why caching at night is so much fun!

[+carleenp]

This thread from a bit back also adds some things to this discussion I think.

[+Glenn]

This particular piece of pseudoscience/urban legend has proven remarkably difficult to eradicate.

Yes, it definitely has. Every time I hear "WAAS drains batteries" or "it makes my unit run slowly" or "it makes me break out in hives" I just want to scream.

 

Use a unit that does WAAS and doesn't suck and these are non-problems. (Well, can't help with the hives thing...)

WAAS made poison ivy grow over one of my caches, and I have proof!

[+TeamRJJO]

The WAAS carrier frequency is that same as that of the GPS signal, so if the flare disrupts GPS signals (which is unlikely, by the way), WAAS will be disrupted as well.

Huh?

 

The reason for using WAAS during solar storms is that WAAS provides near-real-time ionospheric delay corrections. The ionosphere changes significantly during solar storms, which means that a non-WAAS GPS unit can experience significant position errors.

 

UPDATE: I found a really cool page that has a downloadable movie of the ionospheric Total Electron Content (TEC) during a solar storm. (The TEC is what causes GPS position errors, because the signals propagate more slowly through high-TEC regions than through low-TEC regions).

Fizzymagic,

 

As I recall, we had a similar discussion about 2 months ago. Here's what I posted then, and it still holds:

 

"What you would see during scintillation would NOT likely be navigation errors. The bit errors that scintillation causes also make the received navigation message fail the built-in parity checks. So, if your user set is designed in accordance with the GPS payload-to-user specification, your receiver wouldn't use that satellite's signal at all. In reality, your receiver would likely have a tough time maintaining signal lock on the satellites, especially those at lower elevation angles. But again, this is a very localized effect."

 

To expand on this....any error you might see as a result of TEC content (before your receiver simply lost lock altogether) might be on the order of a couple NANOseconds more delay. That equates to a few feet more error than you might otherwise see.

 

Peace,

TeamRJJO

[+fizzymagic]

To expand on this....any error you might see as a result of TEC content (before your receiver simply lost lock altogether) might be on the order of a couple NANOseconds more delay.  That equates to a few feet more error than you might otherwise see.

Hmm. I thought you agreed with me last time. I'm sorry, but from everything I have read, you are incorrect.

 

Let's start with the Wikipedia entry:

The Ionosphere is one of the leading causes of GPS error. The speed of light varies due to atmospheric conditions. As a result, errors greater than 10 metres may arise. To compensate for these errors, the second frequency band L2 was provided. By comparing the phase difference between the L1 and L2 signals, the error caused by the ionosphere can be calculated and eliminated.

 

And from here:

Other Bias Error sources;

Unmodeled ionosphere delays: 10 meters. The ionosphere is the layer of the atmosphere from 50 to 500 km that consists of ionized air. The transmitted model can only remove about half of the possible 70 ns of delay leaving a ten meter un-modeled residual.

 

And this.

 

Also, read this.

 

Garmin mentions it.

 

From this page:

Since SA (selective availability) is deactivated, the largest single source of error in GPS position determination is the signal delay in the ionosphere. Being able to correct these errors significantly increases the accuracy of every GPS receiver that is able to process WAAS/EGNOS data.

 

Now it's certainly possible that everything I have read is wrong and that the ionospheric corrections are only on the order of a nanosecond or so. But in order for me to accept that, I'd need to see some evidence. And probably some explanation for the existence of dual-frequency receivers, too.

 

Until then, since I know that the TEC can vary by a large amount during solar storms, I will continue to claim that the ionospheric corrections from WAAS help position accuracy significantly during solar storms.

[WH]

I have found 700+ caches to date without WAAS. While I don't deny that it does help with GPS accuracy, I havent needed it so far so I can't justify the addtional battery drain.

[+budd-rdc]

  I'm not quite sure what you all are saying, but would solar flares make GPS units go a little crazy. I was out caching yesterday (Thurs) in the afternoon and my GPS was .25 miles off from the hides. I know of another person who's GPS was so whacked that he gave up. When I tried again in the evening, both units worked fine. I'm just trying to figure out if it was my GPS or something else.

I know that several months ago, people in the area were having similar problems during the day. I checked the link both fizzy and StarBrand provided, and there were Solar Radiation Storm (S2) and Radio Blackout (R3) activities in the last 24 hours. Not sure if those caused the anomaly that you described.

 

The most I've seen my GPSr jump has been about 200' so far, but I think those were due to tall buildings, trees, and power lines.

[+VegasCacheHounds]

The WAAS satellties are low on the horizon from here so unless I was standing in a wide open field, I wouldnt pick them up anyways.

<sarcasm>

 

Really? I didn't know that people in MA couldn't get satellite TV! That's amazing!

 

</sarcasm>

 

Your post is nonsense. The WAAS satellites are not low on the horizon from your location. From Boston, for example, the AOR-W WAAS satellite is at an elevation of 38 degrees, which is hardly "low on the horizon." In fact, it's are a lot higher in the sky for you than either WAAS satellite is here in California, and I rarely have any trouble getting WAAS corrections. Maybe you need a better receiver.

 

Seriously. I find it puzzling that people from the Northeast seem to think the WAAS satellites are so hard to see. They aren't! Even from Bar Harbor, Maine, the elevation of AOR-W is almost 37 degrees. ALmost all of Europe is north of MA, and they don't have any trouble with EGNOS. If you were near the Arctic Circle, I could see having some trouble, but there is no problem seeing the WAAS satellites from anywhere in the continental US.

 

So please indulge my curiosity: where did you get the idea that the WAAS satellites are "low on the horizon" from your position?

 

(BTW: if anyone is interested in calculating these numbers for their position, there is a neat website that will do it. AOR-W, the WAAS satellite over the Western Atlantic, is on INMARSAT 3F4, at W 54 degrees, and POR, the WAAS satellite over the Pacific, is on INMARSAT 3F3, at E 178 degrees.)

Wow, I had no idea that WAAS was being run off of the Inmarsat birds! Thats cool, one more connection between my hobby and my work. I work for one of the major US retailers/service providers of Inmarsat. Amazing that I didn't know this little tidbit of information.

Man, angst can lead to good things

[+budd-rdc]

I have found 700+ caches to date without WAAS. While I don't deny that it does help with GPS accuracy, I havent needed it so far so I can't justify the addtional battery drain.

Well, consider yourself lucky. Neither of my GPSr have WAAS so I don't have that luxury.

 

My brother's GPSmap 60c's WAAS is turned on all the time, and when the hider posts spot-on coordinates, we can cut the search time short. With WAAS, you can find more caches before your battery is drained than without WAAS.

[+TeamAO]

The WAAS satellties are low on the horizon from here so unless I was standing in a wide open field, I wouldnt pick them up anyways.

I believe that is the case for me as well.

[+TeamAO]

I have found 700+ caches to date without WAAS. While I don't deny that it does help with GPS accuracy, I havent needed it so far so I can't justify the addtional battery drain.

True...

 

Once I reach within 50 feet of the cache, I usually shut the GPS off and search for hiding places. I have more fun doing so. If in heavy groundcover I may travel closer to the cache, but usually without WAAS I obtain an accuracy of +/- 10 feet. Which I believe is just as good as with WAAS on.

[+fizzymagic]

The WAAS satellties are low on the horizon from here so unless I was standing in a wide open field, I wouldnt pick them up anyways.

I believe that is the case for me as well.

It's not. From Pittsburgh, AOR-W is at an elevation of 36 degrees. That's quite high in the sky.

 

Here in Northern CA, the elevation of the POR satellite is 15 degrees and the AOR-W is only at an elevation of 8.8 degrees. As I said before, I rarely have any trouble picking up either.

 

I remain unable to understand the persistent myth that the WAAS satellite is "near the horizon" in the northeastern US. It is not.

[+CompassCollector]

Following up, Sky & Telescope's "Astro Alerts" says that the energetic sunspot complex that caused the X17 flare earlier this week will likely remain active as it transits the face of the sun during the next two weeks. Since the X17 flare several highly energetic events have been observed including one X5 flare.

 

Current proton density in the earth's vicinity is approximately 100x "normal" background levels. The additional radiation is expected to have potentially adverse affects on sattelites, including degredation of solar cells and additional drag caused by the heating and expansion of the outer layers of the atmosphere (this would not affect geosynchronous orbits, but rather sattelites in Near Earth Orbit).

 

Addional flares and associated CME events could create sustained problems for sattelites and for radio transmissions over the next two weeks.

 

Thanks, fizzymagic, for the information.

Edited September 9, 2005 by CompassCollector

[+budd-rdc]

I went to my favorite ADJUSTED benchmark within the hour, and have the following to report under S2/R1 conditions:

 

AA1871: N 37° 19.883, W 122° 04.989

eTrex: N 37° 19.883, W 122° 04.990

Magellan: N 37° 19.884, W 122° 04.989

 

Oh well, no noticeable effects of solar storm. I may have to try it at high noon next time.

[+JohnnyVegas]

This is true, but the effect is more pronounced on the lower lower frequencies,

Bellow 50 megs. GPS signals are in the microwave region of the spectrum and the effect should not be all the noticable...

The ionospheric TEC is the single largest source of GPS position uncertainty. The effect is quite noticeable indeed.

Solar flares effect skywave propagation, These are communiocations that are bounced off the ionoshere. The E region on the ionosphere, the area about 60-70 miles above the earth is most useful for bouncing radio signals off the ionoshere durring daylight hours. THe F region, 100-260 above the earth is most usefull at night. When there is a solar flare the ionization of the ionosphere increases and D region absorption increases, the D region is 30-60 miles above the earth. At this time the D region can absorbe low frequencies communications, this is called Sudden ionospheric disturbance (SID) this would include shortwave comunications, commercial radio broadcast, and other communications that occur in frequencies of 30MHz and lower, on a rare occasion a solar flare can effect 50MHz staions and very rarley 140Mhz, the travel time for the effects of a solar to reach the earth is 8 minutes.

 

This is why sattelites operated in higher frequencies. 440 MHz and higher. He higher frquencies pass very easily through the ionoshere with a minimum amout of power, just a few watts is all that is needed. By the way, low frequncies communications have improved over the past few days, so I solar flare was not a big deal.

[+Mopar]

I have found 700+ caches to date without WAAS. While I don't deny that it does help with GPS accuracy, I havent needed it so far so I can't justify the addtional battery drain.

I have found 1000 caches with WAAS turned on, and have never gotten poison ivy while caching. So obviously WAAS prevents PI!

 

Seriously though, if WAAS has an effect on battery life, I haven't seen it. A set of fully charged batteries usually last me all day caching; what more do I want? I've seen a much greater drain from using the built in compass.

 

I went searching for specs, and this is what I came up with for a Garmin 60CS (a popular GPS for caching).

Simulator mode (not accessing any satellites) draws 38ma

Searching for satellites (attempting to access ALL satellites) draws 71ma

Backlight low: add 23ma

Backlight med: add 44ma

Backlight max: add 100ma

Compass ON: add 40ma

 

If there is only a 33ma difference between no satellites and all of them, how bad can the one WAAS sat be during normal use? Especially compared to the compass feature that so many cachers use.

Edited September 10, 2005 by Mopar

[+TeamRJJO]

To expand on this....any error you might see as a result of TEC content (before your receiver simply lost lock altogether) might be on the order of a couple NANOseconds more delay.  That equates to a few feet more error than you might otherwise see.

Hmm. I thought you agreed with me last time. I'm sorry, but from everything I have read, you are incorrect.

 

Let's start with the Wikipedia entry:

The Ionosphere is one of the leading causes of GPS error. The speed of light varies due to atmospheric conditions. As a result, errors greater than 10 metres may arise. To compensate for these errors, the second frequency band L2 was provided. By comparing the phase difference between the L1 and L2 signals, the error caused by the ionosphere can be calculated and eliminated.

 

And from here:

Other Bias Error sources;

Unmodeled ionosphere delays: 10 meters. The ionosphere is the layer of the atmosphere from 50 to 500 km that consists of ionized air. The transmitted model can only remove about half of the possible 70 ns of delay leaving a ten meter un-modeled residual.

 

And this.

 

Also, read this.

 

Garmin mentions it.

 

From this page:

Since SA (selective availability) is deactivated, the largest single source of error in GPS position determination is the signal delay in the ionosphere. Being able to correct these errors significantly increases the accuracy of every GPS receiver that is able to process WAAS/EGNOS data.

 

Now it's certainly possible that everything I have read is wrong and that the ionospheric corrections are only on the order of a nanosecond or so. But in order for me to accept that, I'd need to see some evidence. And probably some explanation for the existence of dual-frequency receivers, too.

 

Until then, since I know that the TEC can vary by a large amount during solar storms, I will continue to claim that the ionospheric corrections from WAAS help position accuracy significantly during solar storms.

Fizzy,

 

I think you're confusing two different things and misreading my earlier post.

 

First, you are absolutely correct that iono correction is one of the biggest contributors to positional error in single-channel receivers. No argument there. And you are also correct that this error is one of the main things WAAS helps fix.

 

Where I'm saying you are incorrect is in what happens during periods of increased solar activity, i.e. a solar flare. The main effect this will have is an increase in ionospheric scintillation or in other words, an increase in TEC. Scintillation causes massive bit flipping in the GPS navigation message, such that your receiver will discard the satellite entirely from it's position calculation. Further, if the scintilllation is bad enough, you won't be able to track the satellite at all.

 

There is a small chance that if the scintillation is light enough, you might see a few extra nanoseconds of delay, but that would be about it before your receiver just stopped using the satellite all together.

 

Peace,

TeamRJJO

Edited September 10, 2005 by TeamRJJO

[+EraSeek]

Where I'm saying you are incorrect is in what happens during periods of increased solar activity, i.e. a solar flare. The main effect this will have is an increase in ionospheric scintillation or in other words, an increase in TEC. Scintillation causes massive bit flipping in the GPS navigation message, such that your receiver will discard the satellite entirely from it's position calculation. Further, if the scintilllation is bad enough, you won't be able to track the satellite at all.

 

There is a small chance that if the scintillation is light enough, you might see a few extra nanoseconds of delay, but that would be about it before your receiver just stopped using the satellite all together.

 

Peace,

TeamRJJO

Forgive me for not being totally knowledgable in this but, it is my understanding that ionospheric scintillation bad enough to cause a disruption of the GPS navigation message only occurs a the very lower latitudes. That is where you will see dropped sats.

 

On the other hand you can still have TEC high enough without scintillation in the upper lattudes to affect slowing of signal and postion error of some significance. This is what is reflected in the reduction of error in the GPS manual. If scintillation causes dropping of a sat for the postion solution, you are missing a sat for postion solution, but if the sat signals of multiple sats are delay due to and active ionosphere, you still have significant postion error. What I have seen in my own tests is that WAAS will improve your postion from maybe 12' down to a few feet on a normal day.

 

As I understand it scintillation will occur during a solar storm but affect only those at lower lattitudes, while those at high latitudes will still recieve a signal but it will be greatly degraded.

 

Is this not correct?

[+EraSeek]

Ouch!

 

[+Glenn]

Ouch!

 

Whats the scale on that? I wonder how far out from the surface that is.

[+fizzymagic]

Where I'm saying you are incorrect is in what happens during periods of increased solar activity, i.e. a solar flare.  The main effect this will have is an increase in ionospheric scintillation or in other words, an increase in TEC.  Scintillation causes massive bit flipping in the GPS navigation message, such that your receiver will discard the satellite entirely from it's position calculation.  Further, if the scintilllation is bad enough, you won't be able to track the satellite at all.

 

There is a small chance that if the scintillation is light enough, you might see a few extra nanoseconds of delay, but that would be about it before your receiver just stopped using the satellite all together.

I understand what you are saying here, and I certainly understand how scintillation can cause bit errors. I am not disputing that bit errors from scintillation can cause problems. I am also clear that WAAS cannot correct for scintillation.

 

But I still disagree with you that large changes in TEC only cause small changes in the ionospheric delay. (I understand that the delay can be represented either as a phase shift or a time delay; I choose to think of it as a time delay.) The decreased velocity for the signals in the ionosphere is directly related to the TEC; in fact, the refractive index for the ionosphere is given by:

 

 

where A is constant, f is the frequency, and Ne is the TEC. Recall that the propagation speed for the signals is:

 

.

 

Since n is close to 1, doubling the TEC roughly doubles the propagation delay.

 

During a normal day, the maximum uncorrected range bias from this delay is about 30 m, or a total delay of about 100 ns, for satellites at the zenith. The delay can be three times as large, or 300 ns, for satellites close to the horizon. At mid latitudes, where most of us live, it is less, though, probably down a factor of 2-3. So the range of delays would be 30-100 ns.

 

Double the TEC, and the delay will (roughly) double. During a solar storm, there can be large low-frequency changes in the TEC in addition to the high-frequency changes that cause scintillation. In fact, from what I have read, during a solar storm it is not unusual for the TEC of the ionosphere to change by a factor of 4 for periods of several hours. At our latitudes, that change would result in an additional delay of 120 - 400 ns, which is a lot larger than the "few nanosecond" delay you claim. It results in pseudorange errors of the order of 30 - 100 m!

 

Now, for an isotropic TEC, these pseudorange errors tend to cancel out, at least for the lat/long position solution, so the primary effect is on the elevation solution (all the satellites are above you, so if all the pseudoranges are too long, it looks like you are at a lower elevation than you actually are). But during a solar storm, the TEC is significantly anisotropic, which can lead to significant position errors.

 

As I understand it, non-WAAS-enabled single-frequency GPS units cannot correct for these effects, making the position errors large during solar storms. WAAS data allows correction for the low-frequency TEC changes, allowing much better accuracy, especially for elevation.

 

If I am wrong about this, I would be most grateful for pointers about where to find better information.

Edited September 10, 2005 by fizzymagic

[+bigdog999]

Well this is what I've found to be true with my GPSMAP 60C in Massachusetts. Most of the caches during the summer times are located under relatively dense tree cover. Under these conditions, the GPSr can't hold onto the WAAS satelites. Leaving WAAS on, under these conditions, causes a noticible increase in battery drain...perhaps because the GPSr continues to try to establish WAAS lock. For myself, I turn WAAS off and usually have +/- 20 ft EPE in moderate tree cover.

[+TeamRJJO]

But I still disagree with you that large changes in TEC only cause small changes in the ionospheric delay.

Fizzy,

 

Again that's not what I'm trying to say. Referencing my original post, simply stated, in practice your receiver will drop lock long before you see a dramatic increase in error as a result of an increase in scintillation caused by a solar flare. For the same reason, WAAS wont be a help because you're going to have problems locking onto the WAAS signal as well.

 

The math you present is 100% sound, no question. But theory and practice are two different things. A doubling of the TEC would cause massive parity errors in your received navigation message, such that your receiver would NEVER use that satellite to generate a position solution. (Just for grins, if your receiver ignored the parity errors, the position solution generated would be completely nonsensical). That assumes that you could even continously track the GPS signal through such a disturbance, which you likely couldn't.

 

As far as citing a source, I will have to go back to some reports that we published circa '92-'94, and that will require some digging. But we used to see this all the time when I was working in the GPS master control station. It was nearly impossible to quantify errors caused by solar flares because the receivers would all lose carrier lock when scintillation started kicking up.

 

Peace,

TeamRJJO

Edited September 11, 2005 by TeamRJJO

[+EraSeek]

Ouch!

 

Whats the scale on that? I wonder how far out from the surface that is.

"an X17 flare (almost off the scale) and an associated CME. If the estimate is correct, that would make it the fifth largest flare ever recorded. "

 

That's about all they say about the size.

[+fizzymagic]

Referencing my original post, simply stated, in practice your receiver will drop lock long before you see a dramatic increase in error as a result of an increase in scintillation caused by a solar flare.

I think you may be greatly overestimating the impact of scintillation on modern, 12-channel GPS receivers. I couldn't find a lot of quantitative data on loss of lock on satellites resulting from scintillation, but I did find one report here on a long-term study of scintillation on the GPS system. From that report:

 

We also analysed the effects of geomagnetic storms in the occurrence of scintillation in several satellites simultaneously. For a day when a major geomagnetic storm occurred, such as the one of November 6th 2001, the probability of 2 satellites being affected by strong phase scintillation (σφ > 0.5) simultaneously was ~2%.

 

Remember that scintillation is much reduced at mid latitudes, and that it is a result of physically small (but large in amplitude) fluctuations in TEC. So while it may be likely to lose some satellites from scintillation-induced bit errors at a given time during a solar storm, it is not likely that you will lose so many simultaneously that the receiver will not be able to form a position solution.

 

At least, that is what I am getting from everything I have read. The WAAS system was changed in 2001 after a solar storm to make it more resistant to solar storms, but, from everything I have read about it, the concern was much more about errors in the model of the ionosphere than it was about bit errors.

 

As always, though, I would be very grateful for any information to the contrary.

[+TeamRJJO]

I think you may be greatly overestimating the impact of scintillation on modern, 12-channel GPS receivers.

I think I can pretty much guarantee that nothing anyone here can buy commercially stacks up against what the Air Force uses to monitor the GPS constellation....

 

Peace,

TeamRJJO

[+Renegade Knight]

...I went searching for specs, and this is what I came up with for a Garmin 60CS (a popular GPS for caching).

Simulator mode (not accessing any satellites) draws 38ma

Searching for satellites (attempting to access ALL satellites) draws 71ma

Backlight low: add 23ma

Backlight med: add 44ma

Backlight max: add 100ma

Compass ON: add 40ma

 

If there is only a 33ma difference between no satellites and all of them, how bad can the one WAAS sat be during normal use? Especially compared to the compass feature that so many cachers use.

That's about 50%. Not all of it WAAS related. The V manual does say it will impact your battery life. Though it makes someone else cringe I also notice a lag on my GPS when WAAS is enabled. But I have not used WAAS on a 60 so I can't say if it makes any difference there.

 

But I can get a WAAS lock and latey how I use the GPS the lag isn't as noticable.

[+fizzymagic]

I think you may be greatly overestimating the impact of scintillation on modern, 12-channel GPS receivers. 

I think I can pretty much guarantee that nothing anyone here can buy commercially stacks up against what the Air Force uses to monitor the GPS constellation....

Good point. So you're saying that the monitoring station would regularly lose lock on all the satellites at once from scintillation during ionospheric storms? Like I said, I couldn't find any good information about that out there...

 

One thing I did find is that the GPS satellites are used to measure the TEC during storms, as described here and here. Since neither made any reference to bit errors from scintillation, and since I can eaily imagine that GPS lock was not required for their measurements, I don't think they say anything about their observations of scintillation.

[+EraSeek]

Did you know you got a thing stuck in your head?

[+TeamRJJO]

Good point. So you're saying that the monitoring station would regularly lose lock on all the satellites at once from scintillation during ionospheric storms? Like I said, I couldn't find any good information about that out there...

 

Fizzy,

 

It would be very sporadic. During scintillation season (~Oct to Jan for monitor stations near the equator), at local sunset, we would see signal strength on the receiver channels fluctuate wildly. Sometimes lock would drop altogether, although since the monitor station receiver channels are hooked up to an atomic frequency standard, the receiver would regain P-code lock fairly quickly. Still, the disruption would be enough that the orbit determination software would typically discard the measurements received during scintillation.

 

We could also check the received navigation message against the uploaded message as an integrity check. As I mentioned before, we would see massive errors in the received message, as a result of scintillaiton. This was a real pain because it could mask a "real" problem on board the satellite, i.e. a processor error or a real broadcast error caused by bit flips due to space environmental effects, etc.

 

Peace,

TeamRJJO

[+danewillow]

This morning on my way to work I saw a large green ball of fire plummeting towards Earth (seriously). Was is caused by the solar flare? Was it an asteroid? Could it be aliens and if so, are they friendly or hostile? How will it affect my geo-caching?