Re: [time-nuts] How well does GPS work in the Arcitic?

[Bob kb8tq]

Hi

Getting back to time …

The “long path” GPS is not going to give you the best time solution in a polar 
region. 
That plus the wonky tropo and ionosphere models for those regions (partly due to
lack of data and partly due to physics) are also going to degrade your time 
solution. 
Bottom line - sure, it works,  as noted in the original post, it does not work 
quite as well
as it does in other regions (like at the equator). 

Bob

> On Aug 15, 2017, at 4:50 PM, Magnus Danielson  
> wrote:
> 
> Hi,
> 
> The pre-cursor system Timation had polar orbit and worked essentially as good 
> in the polar area as at the equator. The inclination of orbits was a 
> compromise for better service while not requiring atomic clocks at the 
> receiver.
> 
> Cheers,
> Magnus
> 
> On 08/15/2017 06:34 PM, Bob kb8tq wrote:
>> Hi
>> The “degradation at the poles” thing was very well understood in the 1970’s 
>> when
>> they came up with the orbit plan. The questions about performance started 
>> being
>> asked quite early. The earliest answer I recall hearing (in the late 70’s) 
>> was that polar
>> operations were not a big part of the system needs.
>> Bob
>>> On Aug 15, 2017, at 8:41 AM, Brent  wrote:
>>> 
>>> Several vessels regularly work the poles and their data is publicly
>>> available.  Here's one from the Healy on a cruise that went to 75N ( at
>>> least).  I haven't looked at the data to know how much is there, but at a
>>> minimum I should think you could look for gaps in the timestamp.
>>> 
>>> http://www.marine-geo.org/tools/search/Files.php?data_set_uid=11624
>>> 
>>> I used to work on the Palmer and never saw a glitch in our systems based on
>>> latitude, although we used them for basic nav only (no 'science' done with
>>> the signals).  We worked both poles and at times (very rarely - only for
>>> drilling operations when we were on DP) had corrections sent to the ship
>>> via satellite (Furgro corrections if I recall correctly).
>>> 
>>> Not sure that the Military wouldn't have been very interested in polar nav
>>> even in the early days of GPS - Subs were regularly transiting and hiding
>>> in the arctic and I've got to think they might have wanted to pop up for a
>>> fix now and again, even with MRU's/gyros.
>>> 
>>> That said, a friend of mine regularly worked on the arctic ice sheet in the
>>> 70-90's and most of his navigation was celestial via theodolite.  He did,
>>> however, have an opportunity to test one of the earliest GPS's on the ice
>>> before it was decommissioned.  Knowing the magnitude of what he had, he
>>> asked and was able to keep the front panel.  I tried to send pics of it to
>>> the list a year or so ago, but they bounced (size I guess).  I've tried to
>>> attach a smaller version to this email.  Front what I can tell, this is the
>>> 21st GPS produced.
>>> 
>>> Brent
>>> 
>>> 
>>> [image: Inline image 1]
>>> 
>>> 
>>> 
>>> On Tue, Aug 15, 2017 at 6:22 AM, David J Taylor via time-nuts <
>>> time-nuts@febo.com> wrote:
>>> 
 The satellite orbits only go so far north?  If you are far enough north for
 that to be a problem, can you pick up the satellites across the pole?
 
 I have several days of NMEA log files from 68 N.  I think it will be simple
 after I have done it, but it may be a while before I get time to plot them.
 Does anybody have (non-Windows) code to that?
 ===
 
 Hal,
 
 GPS worked fine for me on a cruise including 80 degrees north.
 
 Cheers,
 David
 --
 SatSignal Software - Quality software written to your requirements
 Web: http://www.satsignal.eu
 Email: david-tay...@blueyonder.co.uk
 Twitter: @gm8arv
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Re: [time-nuts] How well does GPS work in the Arcitic?

[Magnus Danielson]

Hi,

The pre-cursor system Timation had polar orbit and worked essentially as 
good in the polar area as at the equator. The inclination of orbits was 
a compromise for better service while not requiring atomic clocks at the 
receiver.


Cheers,
Magnus

On 08/15/2017 06:34 PM, Bob kb8tq wrote:

Hi

The “degradation at the poles” thing was very well understood in the 1970’s when
they came up with the orbit plan. The questions about performance started being
asked quite early. The earliest answer I recall hearing (in the late 70’s) was 
that polar
operations were not a big part of the system needs.

Bob



On Aug 15, 2017, at 8:41 AM, Brent  wrote:

Several vessels regularly work the poles and their data is publicly
available.  Here's one from the Healy on a cruise that went to 75N ( at
least).  I haven't looked at the data to know how much is there, but at a
minimum I should think you could look for gaps in the timestamp.

http://www.marine-geo.org/tools/search/Files.php?data_set_uid=11624

I used to work on the Palmer and never saw a glitch in our systems based on
latitude, although we used them for basic nav only (no 'science' done with
the signals).  We worked both poles and at times (very rarely - only for
drilling operations when we were on DP) had corrections sent to the ship
via satellite (Furgro corrections if I recall correctly).

Not sure that the Military wouldn't have been very interested in polar nav
even in the early days of GPS - Subs were regularly transiting and hiding
in the arctic and I've got to think they might have wanted to pop up for a
fix now and again, even with MRU's/gyros.

That said, a friend of mine regularly worked on the arctic ice sheet in the
70-90's and most of his navigation was celestial via theodolite.  He did,
however, have an opportunity to test one of the earliest GPS's on the ice
before it was decommissioned.  Knowing the magnitude of what he had, he
asked and was able to keep the front panel.  I tried to send pics of it to
the list a year or so ago, but they bounced (size I guess).  I've tried to
attach a smaller version to this email.  Front what I can tell, this is the
21st GPS produced.

Brent


[image: Inline image 1]



On Tue, Aug 15, 2017 at 6:22 AM, David J Taylor via time-nuts <
time-nuts@febo.com> wrote:


The satellite orbits only go so far north?  If you are far enough north for
that to be a problem, can you pick up the satellites across the pole?

I have several days of NMEA log files from 68 N.  I think it will be simple
after I have done it, but it may be a while before I get time to plot them.
Does anybody have (non-Windows) code to that?
===

Hal,

GPS worked fine for me on a cruise including 80 degrees north.

Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
Twitter: @gm8arv
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Re: [time-nuts] How well does GPS work in the Arcitic?

[paul swed]

I have been watching the thread and there is no reason for GPS not to work
at the poles.
Granted there can be solar events that upset it with things like severe
multi-path but in general if the skies not glowing its most likely just
fine. Also I believe the sats are somewhat low in the sky.
Skips comment makes sense on the 90 degrees. I can see how that math would
get tricky and its a general use-case that most likely someone said so
what
 On the north pole in an aircraft you would most likely rarely ever be
exactly at that point and in a plane it would not be all that long.
Regards
Paul
WB8TSL


On Tue, Aug 15, 2017 at 3:04 PM, Skip Withrow 
wrote:

> Hello Time-Nuts,
>
> I can attest that GPS works fine at the poles, though my experience was at
> the South Pole.  Every year the USGS goes to the South Pole to mark the
> geographic pole.  Since the ice is moving 10 meters per year at the pole
> the pole appears to march across the ice.
>
> One year ('97-'98 I believe) I took my GPS II and sat it on the choke ring
> antenna the USGS had set up.  It read S89°59'59" latitude.  I was
> impressed!  We waited a bit to see if it would ever read 90° but it did
> not.  It just wandered around a bit.  My speculation is that the math blows
> up at 90° so it never goes there.
>
> I have a picture of the event as well.  If I get some time this evening
> I'll have to scan it and post.
>
> Yes, I agree that the HDOP is better at the poles and the VDOP worse, but
> GPS works perfectly well anywhere on earth (for most purposes).
>
> Regards,
> Skip Withrow
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Re: [time-nuts] How well does GPS work in the Arcitic?

[Bob kb8tq]

Hi

The “degradation at the poles” thing was very well understood in the 1970’s when
they came up with the orbit plan. The questions about performance started being 
asked quite early. The earliest answer I recall hearing (in the late 70’s) was 
that polar
operations were not a big part of the system needs.  

Bob


> On Aug 15, 2017, at 8:41 AM, Brent  wrote:
> 
> Several vessels regularly work the poles and their data is publicly
> available.  Here's one from the Healy on a cruise that went to 75N ( at
> least).  I haven't looked at the data to know how much is there, but at a
> minimum I should think you could look for gaps in the timestamp.
> 
> http://www.marine-geo.org/tools/search/Files.php?data_set_uid=11624
> 
> I used to work on the Palmer and never saw a glitch in our systems based on
> latitude, although we used them for basic nav only (no 'science' done with
> the signals).  We worked both poles and at times (very rarely - only for
> drilling operations when we were on DP) had corrections sent to the ship
> via satellite (Furgro corrections if I recall correctly).
> 
> Not sure that the Military wouldn't have been very interested in polar nav
> even in the early days of GPS - Subs were regularly transiting and hiding
> in the arctic and I've got to think they might have wanted to pop up for a
> fix now and again, even with MRU's/gyros.
> 
> That said, a friend of mine regularly worked on the arctic ice sheet in the
> 70-90's and most of his navigation was celestial via theodolite.  He did,
> however, have an opportunity to test one of the earliest GPS's on the ice
> before it was decommissioned.  Knowing the magnitude of what he had, he
> asked and was able to keep the front panel.  I tried to send pics of it to
> the list a year or so ago, but they bounced (size I guess).  I've tried to
> attach a smaller version to this email.  Front what I can tell, this is the
> 21st GPS produced.
> 
> Brent
> 
> 
> [image: Inline image 1]
> 
> 
> 
> On Tue, Aug 15, 2017 at 6:22 AM, David J Taylor via time-nuts <
> time-nuts@febo.com> wrote:
> 
>> The satellite orbits only go so far north?  If you are far enough north for
>> that to be a problem, can you pick up the satellites across the pole?
>> 
>> I have several days of NMEA log files from 68 N.  I think it will be simple
>> after I have done it, but it may be a while before I get time to plot them.
>> Does anybody have (non-Windows) code to that?
>> ===
>> 
>> Hal,
>> 
>> GPS worked fine for me on a cruise including 80 degrees north.
>> 
>> Cheers,
>> David
>> --
>> SatSignal Software - Quality software written to your requirements
>> Web: http://www.satsignal.eu
>> Email: david-tay...@blueyonder.co.uk
>> Twitter: @gm8arv
>> ___
>> time-nuts mailing list -- time-nuts@febo.com
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>> 
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Re: [time-nuts] How well does GPS work in the Arcitic?

[Brent]

Several vessels regularly work the poles and their data is publicly
available.  Here's one from the Healy on a cruise that went to 75N ( at
least).  I haven't looked at the data to know how much is there, but at a
minimum I should think you could look for gaps in the timestamp.

http://www.marine-geo.org/tools/search/Files.php?data_set_uid=11624

I used to work on the Palmer and never saw a glitch in our systems based on
latitude, although we used them for basic nav only (no 'science' done with
the signals).  We worked both poles and at times (very rarely - only for
drilling operations when we were on DP) had corrections sent to the ship
via satellite (Furgro corrections if I recall correctly).

Not sure that the Military wouldn't have been very interested in polar nav
even in the early days of GPS - Subs were regularly transiting and hiding
in the arctic and I've got to think they might have wanted to pop up for a
fix now and again, even with MRU's/gyros.

That said, a friend of mine regularly worked on the arctic ice sheet in the
70-90's and most of his navigation was celestial via theodolite.  He did,
however, have an opportunity to test one of the earliest GPS's on the ice
before it was decommissioned.  Knowing the magnitude of what he had, he
asked and was able to keep the front panel.  I tried to send pics of it to
the list a year or so ago, but they bounced (size I guess).  I've tried to
attach a smaller version to this email.  Front what I can tell, this is the
21st GPS produced.

Brent


[image: Inline image 1]



On Tue, Aug 15, 2017 at 6:22 AM, David J Taylor via time-nuts <
time-nuts@febo.com> wrote:

> The satellite orbits only go so far north?  If you are far enough north for
> that to be a problem, can you pick up the satellites across the pole?
>
> I have several days of NMEA log files from 68 N.  I think it will be simple
> after I have done it, but it may be a while before I get time to plot them.
> Does anybody have (non-Windows) code to that?
> ===
>
> Hal,
>
> GPS worked fine for me on a cruise including 80 degrees north.
>
> Cheers,
> David
> --
> SatSignal Software - Quality software written to your requirements
> Web: http://www.satsignal.eu
> Email: david-tay...@blueyonder.co.uk
> Twitter: @gm8arv
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Re: [time-nuts] How well does GPS work in the Arcitic?

[David J Taylor via time-nuts]

The satellite orbits only go so far north?  If you are far enough north for
that to be a problem, can you pick up the satellites across the pole?

I have several days of NMEA log files from 68 N.  I think it will be simple
after I have done it, but it may be a while before I get time to plot them.
Does anybody have (non-Windows) code to that?
===

Hal,

GPS worked fine for me on a cruise including 80 degrees north.

Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
Twitter: @gm8arv 


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Re: [time-nuts] How well does GPS work in the Arcitic?

[Bill Beam]

On Mon, 14 Aug 2017 18:19:56 -0700, jimlux wrote:

>On 8/14/17 5:58 PM, Bill Beam wrote:
>> GPS orbit inclination is 50-60deg.

>55 degrees

Current TLE show I= low of 51.7 to I= high of 56.6.


>> At my latitude of 65N satellites are about 15deg above the horizon to the 
>> north.

>That would be for satellites that are "over the pole" with respect to you?


yes

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Bill Beam
NL7F



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Re: [time-nuts] How well does GPS work in the Arcitic?

[jimlux]

On 8/14/17 6:15 PM, Bob kb8tq wrote:

Hi

If you are at ICBM mid course altitudes, there are a *lot* of sat’s visible ….
(at least compared to being on the ground).


But do you get good VDOP?
I don't know how high the typical ICBM trajectory goes, I assumed it's 
fairly low (why burn to get higher and take longer), say, 1000 km.  So 
in polar regions, there's still nothing above you if you're at 80 
degrees latitude. The highest latitude the satellite gets is 55 degrees.



Maybe you can pick up VDOP from satellites that are "below" you (grazing 
the earth?)

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Re: [time-nuts] How well does GPS work in the Arcitic?

[jimlux]

On 8/14/17 5:58 PM, Bill Beam wrote:

GPS orbit inclination is 50-60deg.


55 degrees


At my latitude of 65N satellites are about 15deg above the horizon to the north.


That would be for satellites that are "over the pole" with respect to you?


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Re: [time-nuts] How well does GPS work in the Arcitic?

[Bob kb8tq]

Hi

If you are at ICBM mid course altitudes, there are a *lot* of sat’s visible ….
(at least compared to being on the ground). 

Bob

> On Aug 14, 2017, at 9:04 PM, jimlux  wrote:
> 
> On 8/14/17 5:12 PM, Bob kb8tq wrote:
>> Hi
>> 
>> At the time all this was figured out, the idea of the military needing nav 
>> at the poles
>> was pretty far fetched. They accepted a bit of degradation in those regions 
>> as a result
>> of this thinking.
>> 
> 
> I don't know about that - I think it was more that it was "good enough" 
> everywhere, all the time.
> 
> And polar nav, pre-GPS, was really tough - Omega had the same ionosphere 
> problems that GPS has, etc.
> 
> I recall reading somewhere that one of the justifications for GPS was more 
> accurate midcourse guidance for ICBMs and those trajectories tend to be 
> polar. OTOH, in that application you also have IMU and (potentially) star 
> tracker data.
> 
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Re: [time-nuts] How well does GPS work in the Arcitic?

[jimlux]

On 8/14/17 5:12 PM, Bob kb8tq wrote:

Hi

At the time all this was figured out, the idea of the military needing nav at 
the poles
was pretty far fetched. They accepted a bit of degradation in those regions as 
a result
of this thinking.



I don't know about that - I think it was more that it was "good enough" 
everywhere, all the time.


And polar nav, pre-GPS, was really tough - Omega had the same ionosphere 
problems that GPS has, etc.


I recall reading somewhere that one of the justifications for GPS was 
more accurate midcourse guidance for ICBMs and those trajectories tend 
to be polar. OTOH, in that application you also have IMU and 
(potentially) star tracker data.


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Re: [time-nuts] How well does GPS work in the Arcitic?

[Bill Beam]

GPS orbit inclination is 50-60deg.
At my latitude of 65N satellites are about 15deg above the horizon to the north.
Regards.

On Mon, 14 Aug 2017 16:45:22 -0700, Hal Murray wrote:


>The satellite orbits only go so far north?  If you are far enough north for 
>that to be a problem, can you pick up the satellites across the pole?

>I have several days of NMEA log files from 68 N.  I think it will be simple 
>after I have done it, but it may be a while before I get time to plot them.  
>Does anybody have (non-Windows) code to that?



>-- 
>These are my opinions.  I hate spam.



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Bill Beam
NL7F



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Re: [time-nuts] How well does GPS work in the Arcitic?

[Bob kb8tq]

Hi

At the time all this was figured out, the idea of the military needing nav at 
the poles
was pretty far fetched. They accepted a bit of degradation in those regions as 
a result
of this thinking.

Bob

> On Aug 14, 2017, at 7:45 PM, Hal Murray  wrote:
> 
> 
> The satellite orbits only go so far north?  If you are far enough north for 
> that to be a problem, can you pick up the satellites across the pole?
> 
> I have several days of NMEA log files from 68 N.  I think it will be simple 
> after I have done it, but it may be a while before I get time to plot them.  
> Does anybody have (non-Windows) code to that?
> 
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] How well does GPS work in the Arcitic?

[jimlux]

On 8/14/17 4:45 PM, Hal Murray wrote:


The satellite orbits only go so far north?  If you are far enough north for
that to be a problem, can you pick up the satellites across the pole?

I have several days of NMEA log files from 68 N.  I think it will be simple
after I have done it, but it may be a while before I get time to plot them.
Does anybody have (non-Windows) code to that?




http://mycoordinates.org/challenges-for-positioning-and-navigation-in-the-arctic/

lack of SBAS (WAAS) is an issue.

HDOP is better, VDOP poorer because of orbit inclination (no satellites 
overhead)


ionospheric effects worse (TEC varies a lot more in polar regions)


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