GPS above 60 degrees

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David Lesher

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Sep 21, 2021, 7:55:25 PM9/21/21
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A friend is engaged in a journey north, as in
Resolute Bay, Nunavut 74.72N 094.97W

I find papers about GPS coverage at ground level. Is there
anything published about coverage at 20-30 thousand feet?

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Terje Mathisen

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Sep 22, 2021, 10:08:44 AM9/22/21
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David Lesher wrote:
> A friend is engaged in a journey north, as in
> Resolute Bay, Nunavut 74.72N 094.97W
>
> I find papers about GPS coverage at ground level. Is there
> anything published about coverage at 20-30 thousand feet?
>
I have been to Svalbard to visit three Degree Confluence Points, all at
78N, so using a GPS far north was a primary reason for going there.

The trip report starts here, you can see that I had very good coverage
even in March 2004:
https://confluence.org/confluence.php?lat=78&lon=16

At those latitudes you have absolutely no issues with GPS coverage
because you are seeing all the sats on the opposite side of the pole.

In fact, I believe I read somewhere than around 55-60 degrees was the
worst coverage for the GPS constellation, but by now we have at least
GPS+Glonass+Galileo, and so far north you will see the chinese setup as
well.

Terje

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- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

David Lesher

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Sep 22, 2021, 7:00:20 PM9/22/21
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Terje Mathisen <terje.m...@tmsw.no> writes:

>I have been to Svalbard to visit three Degree Confluence Points, all at
>78N, so using a GPS far north was a primary reason for going there.

>The trip report starts here, you can see that I had very good coverage
>even in March 2004:
>https://confluence.org/confluence.php?lat=78&lon=16


Ironically, they were headed to BGTL/Svalbard, but they were
denied landing permission there.

They now think their issue is their flight control system is
upset by the 20 degree difference between magnetic and true
north; this started at 73N.

Alan Browne

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Oct 1, 2021, 4:05:05 PM10/1/21
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On 2021-09-21 19:55, David Lesher wrote:
> A friend is engaged in a journey north, as in
> Resolute Bay, Nunavut 74.72N 094.97W
>
> I find papers about GPS coverage at ground level. Is there
> anything published about coverage at 20-30 thousand feet?

No issues, although at ground level he might not get WAAS coverage.
At altitude he should get WAAS as well.

Even at 45° N, here, I see sats over Russia from ground level.


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Alan Browne

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Oct 1, 2021, 4:07:02 PM10/1/21
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On 2021-09-22 19:00, David Lesher wrote:
> Terje Mathisen <terje.m...@tmsw.no> writes:
>
>> I have been to Svalbard to visit three Degree Confluence Points, all at
>> 78N, so using a GPS far north was a primary reason for going there.
>
>> The trip report starts here, you can see that I had very good coverage
>> even in March 2004:
>> https://confluence.org/confluence.php?lat=78&lon=16
>
>
> Ironically, they were headed to BGTL/Svalbard, but they were
> denied landing permission there.
>
> They now think their issue is their flight control system is
> upset by the 20 degree difference between magnetic and true
> north; this started at 73N.

Should be using grid compass, not magnetic north that far north.

David Lesher

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Oct 16, 2021, 8:51:31 AM10/16/21
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It occurs to me that one of the systems could have put some/all
of its birds in polar orbits. With such added to the mix,
there's be no high-latitude shortcomings.

Higher launch costs, however.

Pondering if generic receivers could cope with them, or they'd
fall over.



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Terje Mathisen

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Oct 16, 2021, 4:08:55 PM10/16/21
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David Lesher wrote:
> It occurs to me that one of the systems could have put some/all
> of its birds in polar orbits. With such added to the mix,
> there's be no high-latitude shortcomings.
>
> Higher launch costs, however.
>
> Pondering if generic receivers could cope with them, or they'd
> fall over.
>
>
>
Really not needed: The current GPS constallation already provides
_better_ coverage at the poles than they do a bit further south (north).

The only thing that gets significantly worse as you're moving from
southern Norway (58 degrees) to Nordkapp (71 degrees) is the vertical
accuracy: Both horizontal position and time resolution stays more or
less the same.

Add in Glonass and Galileo and you'll get pretty good positional
accuracy everywhere with a clear sky view.

Alan Browne

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Oct 16, 2021, 6:32:53 PM10/16/21
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On 2021-10-16 08:51, David Lesher wrote:
> It occurs to me that one of the systems could have put some/all
> of its birds in polar orbits. With such added to the mix,
> there's be no high-latitude shortcomings.
>
> Higher launch costs, however.
>
> Pondering if generic receivers could cope with them, or they'd
> fall over.

There are no significant high latitude shortcomings for basic GPS
service. At the north pole you have a ton of satellites in view.

If you had 6 polar orbit satellites, then there would no coverage
directly over the pole most of the time v. the existing constellation.

I suppose you could low orbit these for more coverage some of the time,
with more sats, or have more sats in the very expensive 12 hour orbit as
well to improve things. But they're "good enough" as is.

What you don't have is SBAS because those sats are geosynchronous
meaning you need a really good "view" close to the horizon (in the icy
wastes probably not a difficult thing...). IAC, the correction data is
not done for extreme high latitudes.

Generic receivers will receive any signal for which a PRN code is known
to exist. Indeed SBAS satellites (WAAS, EGNOS, etc.) "emulate" the
military C/A signal to transmit data to the receiver (this includes
positioning data (WAAS) as well as correction data. Of course they use
a PRN that is different from the US Air Force "set".
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