[Talk-us] Website showing the best time to survey with GPS.

[Kevin Kenny]

On Wed, Jun 26, 2019 at 6:20 PM Eric H. Christensen via Talk-us
<talk-us at openstreetmap.org> wrote:
> I was told there was a website that forecasted the best times to do survey work with GNSS based upon diversity of satellites in the sky, solar activity, etc. Does anyone know what site this is?

Nowadays, the constellations are dense enough (particularly if you can
use GPS/GLONASS/Galileo/BaiDou) that a consumer-grade GPS receiver is
unlikely to see a difference based on satellite diversity. (It's
different, possibly, if there's a failed satellite and no on-orbit
spare, or the on-orbit spare hasn't been moved into position, and
there the sites like https://www.gnssplanning.com/ will give you
useful information.)

The GPS signal is more stable by night and in clear weather.

A bigger effect is signal absorption.  There's one trail near me for
which my mapping involves considerable guesswork, because there's
dense coniferous tree coverage (nothing viisible even in winter
aerials), and the trail goes down into a couple of itty-bitty slot
canyons where all the sky that the receiver can see is directly
overhead, and a little patch to the north where the satellites seldom
cross. There are also cliff faces that set up nice reflections of the
RF signal, so sometimes the receiver's computed position is false.
It's pretty wonky. I bet I could control the effects by using a
survey-grade GPS receiver, setting it on a solid tripod, and giving it
an hour or two of integration time, but I don't have such a device,
nor do I have the time to do that for each trackpoint.

Space weather is another significant effect, but right now we're close
to sunspot minimum, and space weather is mostly quiet.
https://www.swpc.noaa.gov/ provides forecasts.
https://www.swpc.noaa.gov/products/alerts-watches-and-warnings alerts
to significant conditions.
https://www.swpc.noaa.gov/impacts/space-weather-and-gps-systems gives
an idea what to look for, and
https://www.gps.gov/cgsic/meetings/2012/comberiate.pdf is a more
advanced discussion of the same thing. The bottom line here for the
Lower 48 + Hawai`i is probably 'don't worry about it unless Kp gets
above about 5 or there's a class M or X flare in progress.'