[time-nuts] How well does GPS work in the Arcitic?
kb8tq at n1k.org
Tue Aug 15 17:04:53 EDT 2017
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).
> On Aug 15, 2017, at 4:50 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> 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.
> On 08/15/2017 06:34 PM, Bob kb8tq wrote:
>> 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.
>>> On Aug 15, 2017, at 8:41 AM, Brent <brent.evers at gmail.com> 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.
>>> 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.
>>> [image: Inline image 1]
>>> On Tue, Aug 15, 2017 at 6:22 AM, David J Taylor via time-nuts <
>>> time-nuts at 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?
>>>> GPS worked fine for me on a cruise including 80 degrees north.
>>>> SatSignal Software - Quality software written to your requirements
>>>> Web: http://www.satsignal.eu
>>>> Email: david-taylor at blueyonder.co.uk
>>>> Twitter: @gm8arv
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