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G P S Question Re Operating in Thick Smoke ?

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G P S Question Re Operating in Thick Smoke ?

Old 31st Dec 2019, 06:31
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G P S Question Re Operating in Thick Smoke ?

Was watching the bushfire reports from SE Aust. and one of the commentators suggested that the responding aircraft may be having trouble with getting continuous GPS reception due smoke....

Is this true?

Can anybody advise whether the smoke particle density actually blocks or hinders the GPS signal from satellites in Space?

Just curious is all.....

Cheers
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Old 31st Dec 2019, 06:39
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Next time I'm doing a GNSS App in thick smoke to the min I'll let you know, if you never hear from me again you'll know yr answer-)

HNY to all who made is this far! -
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Old 31st Dec 2019, 06:49
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There was commentary about the thick smoke affecting the HF Marine Band during the recent Sydney to Hobart, so I guess RF interference from the smoke is possible. GPS is an incredibly weak signal after-all, but I'm certainly not an expert.
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Old 31st Dec 2019, 07:32
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I wonder if it has anything to do with the same conditions that produce Pyrocumulonimbus and if it's the static build up that causes the lightning also affects GPS?
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Old 31st Dec 2019, 07:33
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thick smoke interference

Yes loss of signal occurs in thick smoke. Its the intermittent and unpredictable nature of the drop outs that cause problems.
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Old 31st Dec 2019, 07:35
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Catseye, honest question here, how does the thick smoke affect the signals? Is it the density of the air and the signal trying to pass through it? or some combination?
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Old 31st Dec 2019, 08:27
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There are multiple effects caused by fire that have an effect on electromagnetic signal propagation. Someone wrote a PhD thesis on this: https://researchonline.jcu.edu.au/2028/2/02whole.pdf

The gist: Particulate matter attenuates signal (present in smoke), but the larger effects are from the signal refraction due to the thermal bubble created by large fires, as well as the electrically charged particles causing large fluctuations in the electron density of the atmosphere - the same effect that occurs when large solar storms hit the earth, although with these the electron density in the near space region (above the atmosphere) is affected.

So yes, this is perfectly conceivable and real!
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Old 31st Dec 2019, 08:29
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I understand it is the high concentration of carbon in the air. Think carbon rods in arc lamps.
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Old 31st Dec 2019, 09:13
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Originally Posted by Ixixly View Post
Catseye, honest question here, how does the thick smoke affect the signals? Is it the density of the air and the signal trying to pass through it? or some combination?
Never had time to consider, usually just trying to remain helo vfr or finding a good hover reference and not running out of gas til the smoke thinned. Similar effect in really heavy fog near fires. No doubt the techheads will have an answer.
The powerlines appearing out of the smoke are a bigger threat

High resolution near cyclones are reported to have a similar effect but managed to avoid that situation.
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Old 31st Dec 2019, 11:31
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People with lots of theory saying yes...
But I was in it today - thick enough that I had to put the instrument lights on, and vis at the MDA was less than 200m (I couldn't see any ground features).
There was no apparent effect on the GPS and no conflict reported between the dual receivers.
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Old 31st Dec 2019, 12:03
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Here's a link to a .PDF document that should contain some answers,- all 224 pages of it.

Radio Propagation In Fire Environments
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Old 31st Dec 2019, 13:04
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Originally Posted by drpixie View Post
People with lots of theory saying yes...
But I was in it today - thick enough that I had to put the instrument lights on, and vis at the MDA was less than 200m (I couldn't see any ground features).
There was no apparent effect on the GPS and no conflict reported between the dual receivers.
The effects in the PHD thesis referenced above would tend to be intermittent and localised so possibly even more dangerous since things could appear to be working fine until their not.

Your observation also supports the theory that it is not the density of the smoke but other (mostly thermal induced) factors that would be significant.

Also to disrupt nav signals they would not need to be blocked, just time modulated (via density changes) enough to cause loss of lock.

Last edited by MurphyWasRight; 31st Dec 2019 at 13:08. Reason: Added time item
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Old 31st Dec 2019, 15:01
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Too busy fighting fires to check
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Old 31st Dec 2019, 23:46
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Thanks Guys / Gals,
Was simply curious - am waay beyond having to rely on such 'new fangled devices'...….

Cheeerrrsss…..
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Old 3rd Jan 2020, 10:59
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MurphyWasRight Indeed with GNSS signals what matters is the signal path between transmitter and receiver and any path delays induced by hot air pockets (doesn't have to be absolute temperature hot, but the gradient between the cold and hot air regions). This can modify the refractivity index of the air to a sufficient degree so that arrival times of GNSS signals are sufficiently out of phase that signal lock is lost, and the receivers determine that no reliable position can be inferred, hence showing no position (rather than an erroneous one). All part of GNSS fail safe mechanisms.
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Old 3rd Jan 2020, 19:27
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5 or so seasons flying helicopters dropping wet stuff on fires and never had a problem with GPS signals down in the smoke.
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Old 4th Jan 2020, 01:44
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Cause and effect? The Canberra hospital is unable to use its MRI due to the smoke, wonder how that works.
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Old 4th Jan 2020, 03:53
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Inside an air-conditioned hospital building, with its filtered air supply, via the air-con.....

That is almost incredible....
Cheers
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Old 4th Jan 2020, 04:22
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Smoke entering the buildings apparently.

https://www.sbs.com.au/news/bushfire...tions-to-close
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Old 4th Jan 2020, 08:23
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There is conflicting anecdotal reports from NBN Skymuster Satellite users regarding effects of smoke.

A bloke in Mallacoota said in an interview he decided against launching into the water due to dodgy gps reception. (mind you, the smoke was so thick it stopped sunlight)

mjb

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