Burying time expired flares

[PilotWolf]

In which case can you explain the calibration process? Assuming you're not merely talking about WAAS or DGPS a lot of forumites, myself included, may not be aware of it.

Basically the GPS unit is calibrated to a known point or datum on the vessel - usually the COG as it should have the least movement due to sea conditions, etc. Laser measurements/plotting of the antenna in relation to this point is done to ensure that if one antenna that is say 5 metres away from it (in an ideal world) the particular unit gives the same position as one 10 metres away from the (same) point. It is then fixed/measured from a known and approved point on land - such as a OS triangulation point. The GPS is 'calibrated' using these measurements to enter offsets in relation to the hydrographic or geological data recording equipment. My point being that the primary and secondary (separate) units are showing different, albeit minor position differences despite the manual corrections to remove any installation errors/differences and as such the £200 unit from XXX marine might not be as good as they claim or people falsely believe.

Sitting alongside, zoomed in on the plotter to the highest scale shows the different fixes from different GPS units - usually the primary and secondary inputs.

Given that even commercial grade plotter 'charts' are only so accurate relying on 10m accuracy is risky, I have regularly been moored on - not next to - various quaysides around the UK and Europe. Radar overlaying on to the plotter confirms the inaccuracy of the charts (yes I am aware of radar's limitations and errors too).

I recall a CAA endorsed lecture about GPS jamming a good few years back (so may not be accurate now) that equated the GPS signal strength to a torch bulb shining from space.

W.

 

[FishyInverness]

- - You ARE ignoring the power issue. Flares do not need to be charged and will still work underwater or if have been submerged, they are self contained and require no electrical input AKA stored chemical energy. Or maybe you are saying the requirement to have a back up battery for GMDSS vessels is a waste of time and pointless?

PW

And you ARE being deliberately obtuse, in order to ignore the power issue yourself and maintain your argument. a PLB does NOT NEED TO BE CHARGED, it also will work after being submerged and are you really saying that you can fire a parachute flare from under the water into the air, really?

A PLB is manufactured with a 5 year battery and requires no electrical input other than that battery, which itself is electro-chemically stored energy. PLB's and EPIRB's have their own stored energy, just like a flare does - in fact a PLB and/or EPIRB can actually be tested to ensure their energy and functionality is there and ready to use, unlike a flare.

AP, You make some valid points, limitation of GPS for a start (Mcmurdo will state accuracy of 61 metres, but I would also challenge anyone to view a flare and be that accurate as to the fired location) but others, like this power issue are weak.

 

[JumbleDuck]

In which case can you explain the calibration process? Assuming you're not merely talking about WAAS or DGPS a lot of forumites, myself included, may not be aware of it.

I think someone has forgotten their GCSE maths lesson on the difference between accuracy and precision.

 

[webcraft]

Are you coming anywhere near Helensburgh in the near future?

It's likely to be December at the earliest before I'm down to Glasgow again, but will PM you if we are heading that way any sooner.

I don't suppose sticking them on the train is a good idea . . .

- W

 

[toad_oftoadhall]

The reason you had to do this was because of the 10m accuracy of GPS making a clear difference between bow and stern, not to improve accuracy.

-The calibration IS for accuracy

In which case can you explain the calibration process? Assuming you're not merely talking about WAAS or DGPS a lot of forumites, myself included, may not be aware of it.

Basically the GPS unit is calibrated to a known point or datum on the vessel - usually the COG as it should have the least movement due to sea conditions, etc. Laser measurements/plotting of the antenna in relation to this point is done. to ensure that if one antenna that is say 5 metres away from it (in an ideal world) the particular unit gives the same position as one 10 metres away from the (same) point.

So LustyD is correct up to this point. [1]

It is then fixed/measured from a known and approved point on land - such as a OS triangulation point

Thanks, how is this measurement made?

The GPS is 'calibrated' using these measurements to enter offsets

AIUI at this point there are two positions. A GPS position, and a position measured using another method relative to a point on land. I must be missing something because I can see how these two positions could be used as a sanity check but I can't see how you can use either position to 'correct' the other because you can't know which is 'most' right. Is the measured position relative to land assumed to be more correct than the GPS position? If so, am I right in guessing that calculated offset to the GPS position gleaned from the fixed point on land is made once & assumed to be unchanged for a period of time? How long?

Thanks for helping, this is all new to me and google is unhelpful in finding details of this calibration process.

[1] Assuming COG = Centre of Gravity, not Course Over Ground. It took me ages to realize that.

 

[Dave99]

is it really that hard to take them to a MRCC? by the way it is illegal to put them in household rubbish

 

[lustyd]

Basically the GPS unit is calibrated to a known point or datum on the vessel - usually the COG as it should have the least movement due to sea conditions, etc. Laser measurements/plotting of the antenna in relation to this point is done to ensure that if one antenna that is say 5 metres away from it (in an ideal world) the particular unit gives the same position as one 10 metres away from the (same) point. It is then fixed/measured from a known and approved point on land - such as a OS triangulation point. The GPS is 'calibrated' using these measurements to enter offsets in relation to the hydrographic or geological data recording equipment. My point being that the primary and secondary (separate) units are showing different, albeit minor position differences despite the manual corrections to remove any installation errors/differences and as such the £200 unit from XXX marine might not be as good as they claim or people falsely believe.

Sitting alongside, zoomed in on the plotter to the highest scale shows the different fixes from different GPS units - usually the primary and secondary inputs.

Given that even commercial grade plotter 'charts' are only so accurate relying on 10m accuracy is risky, I have regularly been moored on - not next to - various quaysides around the UK and Europe. Radar overlaying on to the plotter confirms the inaccuracy of the charts (yes I am aware of radar's limitations and errors too).

I recall a CAA endorsed lecture about GPS jamming a good few years back (so may not be accurate now) that equated the GPS signal strength to a torch bulb shining from space.

W.

So you're now saying that something which is not accurate to within 10m is worth putting a 5m correction in for calibration? What a strange argument to make!

 

[lustyd]

- So which SH equipment is this?
- I am not confused at all, thank you. However I have no idea what you mean by CG broadcast requests - just like your other misunderstandings of phrases/equipment/terminology.

I believe all of the Standard Horizon radios support position requests to individual stations. The coastguard do an all stations position request - this is what a broadcast is.

Since you'll probably argue about this again I'll supply a quote and a link to a post by someone working for the coastguard:

There is another important function which you won't even know when we use it - we can geographically poll an area for vessels, which we do quite frequently now. It's used instead of the "any vessels" broadcast when we may need assistance with another incident - so for example if we need a bot capable of pulling another away from rocks quickly, we'll poll the immediate area and then filter out anything unsuitable, before contacting those that might help. I can get an area poll back in about a third of the time it would take to put out an "all vessels" bx.

http://www.ybw.com/forums/showthread.php?288517-DSC-Usage/page2

 

[Woodlouse]

So you're now saying that something which is not accurate to within 10m is worth putting a 5m correction in for calibration? What a strange argument to make!

You can figure out how much it's out by and adjust accordingly to correct any error. You'll have to do this on a daily basis though. GPS limitations are down to atmospherics and when I was working on survey boats, not too many years ago, I was told that your average GPS will rarely be more accurate than 15 metres or so. Differential GPS will improve on that, but only when it has a signal from a shore station.

 

[lustyd]

You can figure out how much it's out by and adjust accordingly to correct any error. You'll have to do this on a daily basis though. GPS limitations are down to atmospherics and when I was working on survey boats, not too many years ago, I was told that your average GPS will rarely be more accurate than 15 metres or so. Differential GPS will improve on that, but only when it has a signal from a shore station.

My GPS watch (Polar RC3 GPS) seems to pinpoint my position to within a metre every day and I have tracks from the last year showing me running on the same paths and almost never beside them. GPS got a lot more accurate when they turned off the selective availability, perhaps you're thinking of before that happenned?

 

[maxi77]

My GPS watch (Polar RC3 GPS) seems to pinpoint my position to within a metre every day and I have tracks from the last year showing me running on the same paths and almost never beside them. GPS got a lot more accurate when they turned off the selective availability, perhaps you're thinking of before that happenned?

I would suggest that is more because a feature of gps is repeatability, this of course did not work well with SA. ?That is why the hobby/sport of geocaching works so well

 

[Woodlouse]

My GPS watch (Polar RC3 GPS) seems to pinpoint my position to within a metre every day and I have tracks from the last year showing me running on the same paths and almost never beside them. GPS got a lot more accurate when they turned off the selective availability, perhaps you're thinking of before that happenned?

Nope. Like I said, it's the atmosphere that is the limiting component and the only way around that is the differential stations on land giving corrections. I think a lot of land based gps mapping software takes the liberty of assuming your on the nearest road or path parallel to your course and plots accordingly.

 

[lustyd]

Nope. Like I said, it's the atmosphere that is the limiting component and the only way around that is the differential stations on land giving corrections. I think a lot of land based gps mapping software takes the liberty of assuming your on the nearest road or path parallel to your course and plots accordingly.

That isn't what's happenning here, I am aware that road systems work like that. The watch has no mapping, and the program(s) I load it into don't change the positions in the GPX files which just contain the raw fixes. I can then overlay onto various maps but this is just an overlay and I can see the various runs, all of which are within a metre or so of one another. If atmospheric conditions affected it that badly then I'd expect over a year to see tens of metres variation.

The people making Galileo seem confident to quote metre accuracy for thier system which will also be affected by the atmosphere.

 

[Woodlouse]

That isn't what's happenning here, I am aware that road systems work like that. The watch has no mapping, and the program(s) I load it into don't change the positions in the GPX files which just contain the raw fixes. I can then overlay onto various maps but this is just an overlay and I can see the various runs, all of which are within a metre or so of one another. If atmospheric conditions affected it that badly then I'd expect over a year to see tens of metres variation.

Then it must be receiving a differential signal as well as the satellite signal.

 

[toad_oftoadhall]

Then it must be receiving a differential signal as well as the satellite signal.

Perhaps it's calibrated to a nearby trig point like the ones on Survey ships!

 

[PilotWolf]

And you ARE being deliberately obtuse, in order to ignore the power issue yourself and maintain your argument. a PLB does NOT NEED TO BE CHARGED, it also will work after being submerged and are you really saying that you can fire a parachute flare from under the water into the air, really?

A PLB is manufactured with a 5 year battery and requires no electrical input other than that battery, which itself is electro-chemically stored energy. PLB's and EPIRB's have their own stored energy, just like a flare does - in fact a PLB and/or EPIRB can actually be tested to ensure their energy and functionality is there and ready to use, unlike a flare.

AP, You make some valid points, limitation of GPS for a start (Mcmurdo will state accuracy of 61 metres, but I would also challenge anyone to view a flare and be that accurate as to the fired location) but others, like this power issue are weak.

No, no point about PLB is that the transmitting frequency is not routinely monitored and many potential rescuers can neither receive or direction find to it. Likewise you state that a 999 call is slower than Falmouth CG picking up a EPIRB alert - that to me is a deliberate sales ploy and unless the satellite is in the right position at the moment of activation is wrong.

I didn't specify firing a rocket flare from underwater, I said they will function underwater and after being submerged.

Sure these guys are grateful for theirs today - http://www.bbc.co.uk/news/uk-england-hampshire-24124011

Polling is NOT a [voice] broadcast.

PW

 

[lustyd]

Who said voice broadcast?! Do you really not understand or are you just trying to be awkward?

 

[NormanS]

In relation to a Mayday call, what on earth is all this fixation about 10 metre accuracy all about?

 

[grumpy_o_g]

To answer the original question, if they contain any perchlorate then they are a nasty pollutant I'm told. I think more modern flares may not but they definitely used to until fairly recently (several years ago they did). Don't bury them please...

This is about the only link I could find on the subject. Didn't read it all but it shows the nice man from the RNLI really knew what he was talking about. http://www.sfdph.org/dph/files/EHSdocs/Green/ExpiredFlaresFacts.pdf

 

[penfold]

It's likely to be December at the earliest before I'm down to Glasgow again, but will PM you if we are heading that way any sooner.

I don't suppose sticking them on the train is a good idea . . .

- W

Possibly not!

I'm on leave for most of December so I'm sure we can work something out.

To answer the original question, if they contain any perchlorate then they are a nasty pollutant I'm told. I think more modern flares may not but they definitely used to until fairly recently (several years ago they did). Don't bury them please...

Don't tell people that, they'll want to use ground up old flares as weedkiller!