Over reliance on GPS

Alpha22 said:
Are we all a bit too reliant on GPS..... it's all good until it goes down, but that could never happen could it??

Well it has and it did.... http://www.bbc.co.uk/news/technology-35463347

Up to 4km errors...???? anyone spot it??
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Relying on any single point of failure is problematic. Paper charts can blow overboard or catch fire in a candle! Best solution is to always know where you are and then when something says something odd you will be aware of it. I mostly rely on GPS plotters for the basic stuff but then I have charts, pilot guides, radar, depth, hand bearing compass, passage plans, mark one eyeball, local knowledge etc etc. The sh1t hits the fan when all of them fail, or I fall overboard!
 
pmagowan said:
Paper charts can blow overboard or catch fire in a candle!
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I take your point in the wider context but...

Where on earth do you keep your charts that they're in danger of being blown overboard? And given that sensible skippers jump down people's throats when they try and put a cup of tea near the chart table....what's a candle doing anywhere near?
 
I wonder where the BBC obtained the unattributed up to 4km error info from?

According to the US Air Force press release, core navigation systems were not affected

(According to the press release, the problem only affected legacy L band time signals but as the statement doesn't give the detail of which band(s) I can't be specific however the implication is that it would only have affected older receivers)

In theory, if all the time signals from the satellite constellation were out by the same interval position fixes would be unaffected and a 13 microsecond error would not be noticeable on the time displayed by the GPS receiver

Even if the time signals were out by varying intervals, the error correction algorithms in the receiver are designed to deal with that although it could degrade the accuracy but I doubt a 4km error or indeed an error much above a few meters. Such a serious degradation of GPS position fixes would have caused horrendous problems for aviation and maritime navigation and I can't find a single report of any such incidents
 
Prof Danielle George needs to find out how GPS works...
"They shouldn't have seen an issue with that because as far as I understand the way they work is they need two frequencies to lock and there are a number of GPS [signals] to look at," she told the BBC.
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The 2 frequencies are from the same satellite and its the differences in propagation that is used to counter errors due to atmospheric conditions.
 
There is absolutely nothing that, with a little imagination, cannot be transformed from a run of the mill minor event into an earth shattering epoc changing disaster for all (wo)mankind

For details please peruse a certain section of the UK press.:)
 
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pmagowan said:
Relying on any single point of failure is problematic. Paper charts can blow overboard or catch fire in a candle! Best solution is to always know where you are and then when something says something odd you will be aware of it. I mostly rely on GPS plotters for the basic stuff but then I have charts, pilot guides, radar, depth, hand bearing compass, passage plans, mark one eyeball, local knowledge etc etc. The sh1t hits the fan when all of them fail, or I fall overboard!
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The rule in sailing boats, is, never take a chart on deck, particularly for that reason.
 
Interesting. I wonder why WAAS/EGNOS/MSAS did not squeak about it. Maybe because it did not introduce a position error. Applications like DAB, which use GPS time, would be more effected. So would banks, but maybe they could afford to heed the warnings and have back-up clocks.
 
RAI said:
Interesting. I wonder why WAAS/EGNOS/MSAS did not squeak about it. Maybe because it did not introduce a position error. Applications like DAB, which use GPS time, would be more effected. So would banks, but maybe they could afford to heed the warnings and have back-up clocks.
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As far as I can ascertain, it did not affect position fixes at all

Banks and other time signal users would probably not have been affected much if at all by a consistent system wide 13ms drift in the time signal (as long as all systems were equally affected it would make no difference)

The problem seems to have been to do with synchronisation of DAB trunk transmissions between the source and the transmitters. There may also be a clue in the statement that the problem only affected "legacy" L band time signals - I wonder if one part of the DAB broadcast chain was using time signals from a different satellite frequency to other parts of the system. That would account for the problems, right enough (but that's a bit of a guess based on scanty information about what actually went on).
 
laika said:
Well that's just asking to have them get rained on and blow overboard :) pilotage notes scribbled down on waterproof notepaper when down below with your charts fit into pockets much better.
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Each to his own, but out of interest, do you mark waypoints and then have manual pilotage notes as well .. in case the plotter fails?
 
gjgm said:
Each to his own, but out of interest, do you mark waypoints and then have manual pilotage notes as well .. in case the plotter fails?
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Ah I should confess at this point that GPS is a backup rather than primary navigational tool for me. My "waypoints" tend to be defined in my notes (scribbled on a pocket-sized waterproof notebook) in terms of transits, bearings and depths. That's not a "holier than thou" stance: We all enjoy being out on the water for different combinations of reasons. I happen to enjoy the challenge of "traditional" nav. Electronic marine data is something I mostly muck about with for fun when ashore :-)
 
laika said:
Ah I should confess at this point that GPS is a backup rather than primary navigational tool for me. My "waypoints" tend to be defined in my notes (scribbled on a pocket-sized waterproof notebook) in terms of transits, bearings and depths. That's not a "holier than thou" stance: We all enjoy being out on the water for different combinations of reasons. I happen to enjoy the challenge of "traditional" nav. Electronic marine data is something I mostly muck about with for fun when ashore :-)
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Totally agree.. each to his own.
Maybe it also has something to do with the boat itself in that paper charts might be a bit more practical on heavy slow boats than faster bouncy ones where attemtping to take a bearing would give a reading range of about 120 degrees !
 
Bru said:
The problem seems to have been to do with synchronisation of DAB trunk transmissions between the source and the transmitters. There may also be a clue in the statement that the problem only affected "legacy" L band time signals - I wonder if one part of the DAB broadcast chain was using time signals from a different satellite frequency to other parts of the system. That would account for the problems, right enough (but that's a bit of a guess based on scanty information about what actually went on).
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Most of the civil systems use the old L1 but they can get and use the carrier from L2 (e.g. like WAAS/EGNOS/MSAS).
I guess the newer IIR, IIF and III satellites are transmitting the new civil signal on L1C, L2C and L5. That would explain the reference to only the old L1 (C/A) signal being effected. I must look out for receivers that can use L1C, L2C and L5, they should have much better performance.
 
laika said:
Well that's just asking to have them get blown overboard :)
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Last August, rounding North Foreland, SWMBO says 'where are we?'. I pick up the chart from the floor on my flybridge, and as I raise it above the wind deflector it disappears straight over my head and off the back of the boat....
 
RAI said:
Most of the civil systems use the old L1 but they can get and use the carrier from L2 (e.g. like WAAS/EGNOS/MSAS).
I guess the newer IIR, IIF and III satellites are transmitting the new civil signal on L1C, L2C and L5. That would explain the reference to only the old L1 (C/A) signal being effected. I must look out for receivers that can use L1C, L2C and L5, they should have much better performance.
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Good info, ta
 
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