GPS affected by cloudy days etc?

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e9999

e9999

Gotta get out there...
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hmmm....
having some trouble with my handheld GPS under heavy clouds. It's not seeing as many sats as strongly as usual. This a.m. when driving around, it couldn't even get a fix. This pm it did, but the signals were weak.
This to be expected or did I get a bum unit?

Ironically enough, I guess, it's when it's stormy or you're in a deep forest, or in a deep canyon that you'd normally want not to be lost, yet that may be when it's working the worst....
 
Although I've read that it could affect it, I have NEVER had a problem with anything weather related impacting satellite reception.

I have a Garmin GPS V.

I have found that it sucks when you're using it for navigation and you're driving on the lower section of a double-decker bridge and you lose reception and don't know which of the exits you need to take until you get reception again, but by then you've missed your exit...it happened to me when I was in Seattle once. Damn, I hate when that happens.
 
Had some serious fast moving storm cover in Tellico two weeks ago, had a detrimental affect on my GPS V, reception went from nearly perfect (8ft accuracy) to under 20ft. I've found that an external active antenna helps in all situations.
 
My Toyota van's OEM navigation system works even through tunnels (how?)

Always works, rain or shine, except when I go to large cities with tall buildings, then it struggles from time to time.

Mot
 
Garmin's top of the line car navigator includes a flux gate compass and connects to you vehicle's speed sensor so that it can continue to navigate during periods of intermittent gps signal reception.
 
I had it happen once in some thick overcast we sometimes get here in Gilroy. I never thought about it happening either, but yeah, it did.
 
Atomospheric conditions can/do effect the accuracy of any GPS receiver. Cloud cover absorbs and reflects the sat signals. The magnitude of this effect will be determined by the receiver, high end less so than consumer handheld and the water content/thickness of the cloud cover IIRC. Alot of this is over come with the new 12 channel receivers as the the geometry of the sats determines the distance of cloud cover the signal must travel through, so those sats on the horizon will have more 'cloud' error and weaker signals than those overhead with a uniform cloud thickness. The 12 channel receiver is able to track 12 sats at the same time, and measure the best signals in real time.

e9999, the only way to overcome this is to try to eliminate as many factors that effect reception, the external antenna. Units inside the car have sat blind spots. Having said this, for navigation I leave my unit on the dashboard. This is usually good enough for me to navigate in the field. When I need an accurate position I take the unit outside and give it about five minutes to get a good average. If I am experiencing problems in the car I try to have the unit upright. Different handheld antennas perform better based on how their antenna is oriented. Quadrapole antennas like to be upright and I forget how the patch antenna likes to be oriented. Most handhelds use a patch antenna.

The last easilly corrected problem with handheld units is power. If you can run it on the DC while in the car is best. I can't remeber who told me this, but once a handheld's battery is about 2/3 exhausted, error and signal acquisition begins to fall off.

Ross
 
all good to know, guys...
went back outside, thick cloud cover (enough that you can look at the sun)
tried again in the open (previous try was in car). Finally got to have 10 or so sats but signal not max unlike previously with clear skies. Took a long time too to get all the sats tracked.
So definitely an effect. Was not able to get better than 30ft accuracy or so.
(Explorist 200)
 
mot said:
My Toyota van's OEM navigation system works even through tunnels (how?)

Always works, rain or shine, except when I go to large cities with tall buildings, then it struggles from time to time.

Mot
Click to expand...

MOT, if I'm not mistaken, the Nav Sys in my 03 has some gyroscopes in there too, so that would do the trick in tunnels...
 
Cloud cover will not have a measureable effect on the types of systems that are being discussed here. Percipitable water vapor can have an effect on the zentih tropospheric delay (ZTD) of a given satellite signal and as was pointed out by GeoRoss, satellites that are closer to the horizon are more effected by atmosphere (the signal has to go through more troposphere and ionoshpere). Ionospheric scintillation and total electron content has a much more significant effect on GPS (and all radio waves). These atmospheric effects are only really noticable on real-time kinematic GPS systems (centimeter accuracy), and geodetic systems that are use for millimeter level positioning.

Cheers,

Jeff (GPS super-freak)
 
A lot of tunnels have a wire strung through to try to prevent radio reception loss. Most were originally installed to help emergency services communicate but most also help the car radio of people driving through.
The wire works for GPS too? My Delorme Earthmate kept at least three sats through Caldecont (sp?) tunnel from Oakland,CA once that I noticed and it's a laptop add-on that doesn't use gyroscopes.
 
I doubt that a GPS will maintain it's tracking in a tunnel (same with on-board nav systems).

IIRC, my GPS manual mentions that if a signal is lost there is some period (you may even be able to set this) where it continues to show that it is tracking, althought it really isn't (I thought mine is at something like 30 seconds) - with the hope that by that time it has reacquired the satelites and figured out where you are before it (the GPS) admits defeat!

Cheers, Hugh
 
Just curious, do any of you guys feel the need to have more than 30ft accuaracy and why.

Honestly, out in the outback, anything less than 100 ft(30m) is more than enough for navigation, especially on roads and trails that are on the map. I use GPS in my work and for navigaiton on 7.5' quads (1:24K) and also 1:100K maps I have never had issues with a hand held just laying on the dash board (it does bounce around alot though). Granted, most of my work is in the desert with few trees, but lots of canyons and mountains. I do occasionaly loose tracking data, but I always have enough to keep located.

Jeff, what kind of GPS super freak are you? I work with guys into geodectic measurements and such, much more freaky than me, but I appreciate it though.

Ross
 
Certainly less of a problem than if you are a pilot or navigating a ship / boat near big rocks! I agree, 30' is generally fine.
 
CDN_Cruiser said:
Certainly less of a problem than if you are a pilot or navigating a ship / boat near big rocks! I agree, 30' is generally fine.
Click to expand...

Good point about boats. There is a cool system really only available to water/air navigation users called WAAS. It sychronizes correction codes to your GPS unit via IIRC radio transmissions which allows very precision and accuracy. The transmitters are mostly near shore and airports right now. I think they are going to deploy more transmitters in the interior, but topograpy will make it problematic.

Ross
 
GeoRoss said:
Good point about boats. There is a cool system really only available to water/air navigation users called WAAS. It sychronizes correction codes to your GPS unit via IIRC radio transmissions which allows very precision and accuracy. The transmitters are mostly near shore and airports right now. I think they are going to deploy more transmitters in the interior, but topograpy will make it problematic.

Ross
Click to expand...

my little inexpensive handheld uses WAAS
 
e9999 said:
my little inexpensive handheld uses WAAS
Click to expand...

If you are near the WAAS transmitters and enable WAAS on your handheld, it will increase your accuracy/precision.
 
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