Deep-fried GPS?

[oldbilbo]

More dire warnings of doom, from the General Lighthouse Authority this time.... reported in Yachting Monthly's news page on here.

"....Of equal concern is the possibility of outages in GPS coverage. According to a report commissioned by the General Lighthouse Authority. ‘GPS is far from robust. Although reliable and accurate for long periods, it can suddenly and unexpectedly fail. In recent years such failures have been due to a range of vulnerabilities: solar disturbances, space-vehicle failures, unintentional radio interference and, increasingly, deliberate jamming.

‘The consequences have included not only the loss of GPS service but, more seriously, positions and velocities shown on ship's displays that without warning became incorrect, yet remained plausible.'

With some GPS systems, they say, outages don't even trigger an alarm. That's worrying on a yacht and downright scary when you think of it happening on the bridge of a fast-moving ship. The report is ominous about reverting to traditional navigation methods, saying would ‘force the mariner to revert to increasingly unfamiliar fallback navigation methods such as chart, compass and visual bearings.'....."

I'm all right, Jack....

....But think of all those fearties who'll not dare venture out of line of sight of their Solent marinas. Shall we see small ads in PBO and YM offering 'Traditional navigator for hire. No boat should go over the horizon without one.'

 

[Madhatter]

So how much will you be charging then ?

 

[mikeinkwazi]

Can somebody tell me what GPS is for? I was given one in '95 but found it useless for getting radio 4 and put it back in the box.

 

[sarabande]

should the name be changed to Global Positing System ?

 

[AntarcticPilot]

Am I allowed to say "Told you so"?

 

[oldbilbo]

Am I allowed to say "Told you so"?

I believe we should consider forming a Guild, you 'n me. Now we need some Entry Qualifications, to keep out the 'hoi polloi'...

And apropos Madhatter's very relevant query, we might consider a starting rate of '2 pints of Butcombe or Wadworth's 6X ( Bass negotiable ) per hour'.

Oh, and Sunday callouts at 'double time'!

 

[elton]

I'd like to read an expert technical explanation for this, because I still don't believe it.

‘The consequences have included not only the loss of GPS service but, more seriously, positions and velocities shown on ship's displays that without warning became incorrect, yet remained plausible.'

How can ionic/electrical/atmospheric interference cause the reception of apparently valid, but incorrect GPS positional data? Note, incorrect rather than inaccurate.

 

[toad_oftoadhall]

I'd like to read an expert technical explanation for this, because I still don't believe it.
How can ionic/electrical/atmospheric interference cause the reception of apparently valid, but incorrect GPS positional data? Note, incorrect rather than inaccurate.

+1

Unless by jamming they mean spoofing of positions. A bit unlikely IMHO. Who the hell is going to spend time following a leisure boat around beaming "plausible but incorrect" data at it!? (Obviously you'd have to pick a specific boat and stick with it or the calculated COG wouldn't ever be "plausible" and the position wouldn't remain plausible for long even if by luck it started that way!)

A cynic might say the "General Lighthouse Authority" are a bit worried that GPS is *so* effective that someone might suggest closing some light houses.

Personally I find light houses far more reassuring than a GPS fix, but no doubt a light house could be spoofed too if we're going to get that paranoid. (It would have the advantage that you wouldn't have to tailor your spoofing to one boat. You could just stick a light characteristic from a real lighthouse in the wrong place and with luck fool a load of boats.) [1]

A few years back we did a poll on YBW. I think over 95 per cent said they're fine with conventional nav & would have no problems whatsoever if GPS packed up.

It's a non-issue.

The 5pc of sailors who can't cope with conventional nav will have to devote an afternoon to picking up enough to sail about a bit, it's not difficult

[1] Why would anyone spoof the position of a leisure boat?

 

[prv]

A cynic might say the "General Lighthouse Authority" are a bit worried that GPS is *so* effective that someone might suggest closing some light houses.

Seems to be t'other way round - Trinity House and their French counterparts are closing things all on their own. If you sit down to apply the corrections to a chart of the Channel, it feels like half the changes are either reducing the ranges of major lights, or removing foghorns. Last batch of changes also took away a couple of large offshore buoys (7-mile range on the light, so not a small thing) and replaced them with virtual marks broadcast by AIS.

A few years back we did a poll on YBW. I think over 95 per cent said they're fine with conventional nav & would have no problems whatsoever if GPS packed up.

It's a non-issue.

Well, they would say that, wouldn't they? If you tried it, I bet a lot of them would find they're not as skilled as they thought they were.

Pete

 

[RobbieW]

Going back to basics, remember that the accuracy of GPS is defined as within x.x metres xx% of the time. With Selective Availability that became x.x+n metres xx-y% of the time. Supposing the interference (however thats caused and remembering that GPS signals are extremely weak) was causing a signal variation giving a 10-15% shift in position its quite possible to imagine scenarios where believable but inaccurate data is presented to a navigator and transmitted on AIS.

In essence GPS does not give an absolute position fix, there will always be some error and that error is variable.

btw, beer is always acceptable but beer tokens are much better

 

[Buck Turgidson]

Every commercial GPS unit ive used in aviation uses RAIM. They issue warnings if integrity is lost. you would need all signals to be in error by perfectly matching amounts to spoof a good receiver.

anyone interested in data rather than rumour can find all they need to know on the egnos website including accuracy levels.
http://egnos-user-support.essp-sas.eu/egnos_ops/service_performances/global/position_error#

 

[elton]

Going back to basics, remember that the accuracy of GPS is defined as within x.x metres xx% of the time. With Selective Availability that became x.x+n metres xx-y% of the time. Supposing the interference (however thats caused and remembering that GPS signals are extremely weak) was causing a signal variation giving a 10-15% shift in position its quite possible to imagine scenarios where believable but inaccurate data is presented to a navigator and transmitted on AIS.

In essence GPS does not give an absolute position fix, there will always be some error and that error is variable.

btw, beer is always acceptable but beer tokens are much better

What does "10-15% shift in position" mean? 10% of what?

The GPS receiver always reports level of accuracy in terms of a circle of specified radius centered on the receiver. There's no reason to assume positional accuracy better than this.

 

[Madhatter]

If man can build it man can fek it up especially if sufficiently motivated. Don't forget this is a military system used to assist the military to carry out its main function, now if that's not sufficient motive I don't know what is and millions of £ - $ AFN -XAF - RUB would be used to find a way of turning the system on itself and leisure users would be acceptable collateral damage.

 

[toad_oftoadhall]

Supposing the interference (however thats caused and remembering that GPS signals are extremely weak) was causing a signal variation giving a 10-15% shift in position

10-15% of what? The DOP? That would be centimeters? Do you think any of the inputs to an EP can be measured within 10-15%?

its quite possible to imagine scenarios where believable but inaccurate data is presented to a navigator and transmitted on AIS.

Not without him knowing about it, though. Also I very much doubt a position with a large HDOP is transmitted on AIS, surely outliers would be discarded? (Not that I've ever seen an big DOP at sea.)

In essence GPS does not give an absolute position fix, there will always be some error and that error is variable.

That error is also quantified and presented to the user.


If the GPS SVs all packed today leisure sailors aren't going to suffer to any large degree because conventional nav is mostly common sense. If you didn't have common sense you could learn how to work out an EP by wrote in minutes, not hours.You could even carry a book on it. Pay someone to tell you the way to Dielette? Really? Can we pack up the hysteria, please?

 

[vyv_cox]

If the GPS SVs all packed today leisure sailors aren't going to suffer to any large degree because conventional nav is mostly common sense. If you didn't have common sense you could learn how to work out an EP by wrote in minutes, not hours.You could even carry a book on it. Pay someone to tell you the way to Dielette? Really? Can we pack up the hysteria, please?

Having sailed well before the advent of GPS I'm afraid I cannot agree. Common sense is all very well but when conditions are poor it is all too easy to get it wrong.

I was given a collection of old PBO magazines dating back to the 1970s. Almost every one contained an article about crossing the channel along the lines of 'we thought we could see the IOW but it turned out to be Poole'. I dare say that some of these were written by people who may have been short of common sense but all of them? Underestimating leeway and cross current, seasickness, simple mistakes, can all contribute to gross errors of position. We have become used to the accuracy of GPS and its loss would change sailing for many people. Not that I am taking too much notice of the original message.

 

[toad_oftoadhall]

If the GPS SVs all packed today leisure sailors aren't going to suffer to any large degree because conventional nav is mostly common sense. If you didn't have common sense you could learn how to work out an EP by wrote in minutes, not hours.You could even carry a book on it. Pay someone to tell you the way to Dielette? Really? Can we pack up the hysteria, please?

Having sailed well before the advent of GPS I'm afraid I cannot agree.

Really? Nothing in your posts contradicts anything I've written. I also sailed before GPS and in the days of selective availability and from the average age on YBW I'd say almost everyone here did (apart from people who started late). I didn't "suffer to any large degree", nor did my peers. As I said above, something like 95pc of YBWers agreed that loss of GPS wouldn't cause them much suffering either.

We have become used to the accuracy of GPS and its loss would change sailing for many people.

Change does not mean "suffering to a large degree".

I was given a collection of old PBO magazines dating back to the 1970s. Almost every one contained an article about crossing the channel along the lines of 'we thought we could see the IOW but it turned out to be Poole'. I dare say that some of these were written by people who may have been short of common sense but all of them? Underestimating leeway and cross current, seasickness, simple mistakes, can all contribute to gross errors of position. We have become used to the accuracy of GPS and its loss would change sailing for many people. Not that I am taking too much notice of the original message.

None of this contradicts my point, nor does it demonstrate that people won't be able to "venture out of line of sight of their Solent marinas" in a post GPS world. In fact it rather seems to be supporting the premise of my question: "Do you think any of the inputs to an EP can be measured within 10-15%? ".

 

[pmagowan]

I really like GPS as a tool and use it most of the time while sailing. I have a garmin integrated system as well as a handheld and an iphone so essentially 3 seperate GPS recievers. Of course, if the signal went down or was significantly altered these would all be useless but then I have charts. I am not an 'extreme sailor' and as such I always know roughly where I am even if I didn't have a GPS or chart. I suppose it depends on your sailing grounds and how many hazzards there are. Normally I know where I left and where I am going to in advance, along with what is in between. Of course it could all go terribly wrong and mistakes happen but this is true even when the GPS is working. The only problem I can see here is if a GPS unit does not let you know that accuracy has dropped below safe levels. My units do so when I am lost I will know I am lost!

 

[Bilgediver]

I'd like to read an expert technical explanation for this, because I still don't believe it.



How can ionic/electrical/atmospheric interference cause the reception of apparently valid, but incorrect GPS positional data? Note, incorrect rather than inaccurate.

This already happens from time to time on aircraft tracking web sites... A rougue position is put into the mixture which might be hundreds of miles of the actual course. In order to reach that position and return to the correct track the plane will fly an erroneous course at an apparently ridiculous speed!

 

[RAI]

They say:- "In recent years such failures have been due to a range of vulnerabilities: solar disturbances, space-vehicle failures, unintentional radio interference and, increasingly, deliberate jamming."
Solar disturbances - could damage satellites, but no GPS satelltes ruined so far since 1985. Does disturb the ionosphere, reduces GPS accuracy, largely corrected by WAAS, EGNOS, MSAS.
Space vehicle failure - happens fairly regularly and end of satellite life, thus GPS has an excess of satellites (32 instead of 24, last time I looked), so no biggy.
Unintentional radio interference - uncommon at sea, more so on land, can result in loss of reception and operation.
Deliberate jamming - occurs during military excersises, which are NOTAMed, occurs a lot the US on land with privacy protection devices, uncommon at sea.

Anyone know how LORAN-C is getting along? Trinity House used to be promoting that as the GPS malady cure-all.

 

[elton]

This already happens from time to time on aircraft tracking web sites... A rougue position is put into the mixture which might be hundreds of miles of the actual course. In order to reach that position and return to the correct track the plane will fly an erroneous course at an apparently ridiculous speed!

You mean the plane appears to fly an erroneous course at a ridiculous speed?