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GPS Does or Does Not Get Effected by Weather?


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I have looked around for an answer to this question and couldn't find it. Weird, since I know I saw it on the site somewhere before!

 

We were out trying to find a cache this weekend and were getting seemingly erratic readings. Then, a huge cloud cover rolled in and we started getting readings that were off by 80 feet. Next, no signal!

 

I am using a Garmin eTrex Legend, if that helps.

 

Thanks for you answers,

 

- netgeist

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There are plenty of techies around here to give you an 'official' answer, but let me share what I've experienced.

 

I've never had a problem with poor signals if I am out in the weather unless I am under tree cover. Under heavy tree cover, it seems like performance suffers noticibly. I've always blamed it on wet leaves.

 

Whenever I feel blue, I start breathing again.

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quote:

"Navstar GPS is a satellite-based radio navigation system developed and operated by the US Department of Defense (DOD). GPS allows land, sea, and airborne users to immediately determine their three-dimensional position, speed and time, 24 hours a day, under all weather conditions, anywhere in the world.


 

That about says it all but GPS is also used for weather forecasting, especially with regards water vapour.

 

However one little cloud (even a huge cloud) isn't going to cause any problems that a recreational receiver will probably detect.

 

If the weather became that extreme (and it has to be extremely extremely extreme) that signal was completely lost (have never heard this occuring) then the last thing one would be worried about would be GPS signal.

 

Cheers, Kerry.

 

I never get lost icon_smile.gif everybody keeps telling me where to go icon_wink.gif

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quote:
Originally posted by Kerry:

If the weather became that extreme (and it has to be extremely extremely extreme) that signal was completely lost (have never heard this occuring) then the last thing one would be worried about would be GPS signal.


 

Noah: "Shem, put the Ark down on Mount Ararat!"

Shem: "I'd love to, Dad, but I can't get satellite lock. This mapping GPS is useless!"

Ham: "Don't worry! I've got the MapQuest map loaded on my laptop!"

Noah: "Well, fine, but send out those doves anyways, once the storm lets up."

 

x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x

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I don't know the offical answer, but here in Oregon I seem to have a tougher time getting a lock on days with a sky full of thick dark clouds. I would think that the GPS signal can be blocked by any object and rain drops are a bunch of tiny objects. You can loose DSS signals with really nasty cloud coverage.

 

smiles_63.gif ---Real men cache in shorts.

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Officially -- unaffected by weather.

 

Real world -- Yes, heavy cloud cover will degrade signal slightly. If you are already receiving a marginal signal then heavy wet clouds may make it worse. Electrical activity in the clouds will do it too.

 

As mentioned earlier tree canopy affects signal and wet canopy even more so. A satellite or two may have just moved out of visibility at the same time as a cloud moved in. I have noticed on some units that accuracy drops as batteries weaken, even though manufacturers claim that does not happen.

 

Combine all the factors (heavy overcast, wet canopy, satellite geometry changing, weakening batteries) and you go from good to bad signal in a hurry.

 

========================================

Friends don't let Friends geocache drunk.

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The GPS system was designed such that it is NOT effected by weather.

 

There is a "rain window" about 1.5Ghz and that is one of the reasons GPS is there. There is almost no attenuation even in the heaviest downpour. (Just a db or two).

 

On the other hand, just a few millimeters of standing water will absorb/reflect 1.5Ghz waves.

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quote:
Originally posted by Dave54:

Officially -- unaffected by weather.

 

Real world -- Yes, heavy cloud cover will degrade signal slightly. If you are already receiving a marginal signal then heavy wet clouds may make it worse. Electrical activity in the clouds will do it too.

 

As mentioned earlier tree canopy affects signal and wet canopy even more so. A satellite or two may have just moved out of visibility at the same time as a cloud moved in. I have noticed on some units that accuracy drops as batteries weaken, even though manufacturers claim that does not happen.

 

Combine all the factors (heavy overcast, wet canopy, satellite geometry changing, weakening batteries) and you go from good to bad signal in a hurry.

 

========================================

Friends don't let Friends geocache drunk.


 

------------------------

5_Rubik.gifMy home page about GPS units and information

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Well now, if you can't get reception in tree cover, but you can in your house, it's the water in the trees and not the wood in your roof. To a point anyway.

 

So standing in fog with cloudcover above you wouldn't expect to have as good of reception.

 

By way of "Proof" while caching in the fog and rain with cloud cover I was consistatnly 50' off while normaly I'm 20' off of a cache when I find it according to the GPS.

 

I'm also a lot more likely to have my GPS think that another spot 40' over is ground zero all of the sudden in fog and rain and cloud cover.

 

Wherever you go there you are.

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I had wondered about this myself, but today I was caching in dense fog with heavy cloud cover and intermittent mist/sprinkles. My reception was fine and my GPSr lead me right to the caches. icon_smile.gif

 

Without question, the greatest invention in the history of mankind is beer. Oh, I grant you the wheel was also a fine invention, but the wheel does not go nearly as well with pizza. - Dave Barry

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Originally posted by MrGigabyte:

There is almost no attenuation even in the heaviest downpour. (Just a db or two).

 

Ok, first a quick point on Decibel Notation (db). A one db drop in RSS (Received Signal Strength) represents a change factor of 1.26. That is, a 25 watt signal will be reduced to (aproximately) 20 watts. A 3 db drop will result in a 50% RSS. So, you can see that your 1 or 2 db drop can be fairly major. I wasn't able to find an exact number (if anyone knows for sure, I would be interested in hearing from them) but typically SHF Satellite transmissions are in the 12 - 20 watt range. When you realize that the old CB radios we all played with in the 70's put out 4 watts, and think about how much farther away that satellite is, well.... The point was also made that GPS was designed NOT to be affected by weather, certainly true, but the basic facts of radio wave propigation mean that ANYTHING between you and the transmitter (satellite) will cause a reduction in signal strength. Clouds, especially if they contain significant water vapour may cause noticable signal attenuation. The short answer to the original question is: Weather WILL affect your GPS reception, but should not normally be noticable. Factors such as time of day, sunspot activity and the design of your GPS antenna and the way you orient it to the satellite will also have an affect.

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I don't understand these numbers, but as they say, looks pretty small to me.

 

"Cloud, Rain, Snow, weather in general does NOT attenuate the GPS signals enough to effect accuracy. As can be seen below, the total atmospheric loss (from all causes including rain, clouds, snow, fog, etc.) is but 2db. This is small compared with other variables. ''

 

L1 and L2 Navigation satellite Signal Power Budget

 

Parameter L1 P-Code L1 C/A-Code L2 P-Code

-----------------------------------------------------------------------------------------------------

User minimum received power -163.0 dBw -160.0 dBw -166.0 dBw

Users linear antenna gain 3.0 dB 3.0 dB 3.0 dB

Free-space propagation loss 184.4 dB 184.4 dB 182.3 dB

Total atmospheric loss 2.0 dB 2.0 dB 2.0 dB

Polarization mismatch loss 3.4 dB 3.4 dB 4.4 dB

Required satellite EIRP +23.8 dBw +26.8 dBw +19.7 dBw

Satellite Antenna gain at 14.3° 13.5 dB 13.4 dB 11.5 dB

worst case Block II off-axis angle

Required minimum satellite antenna +10.3 dBw +13.4 dBw +8.2 dBw

Input power 10.72W 21.88W 6.61W

 

4497_300.jpg

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I live in the Upper Peninsula of Michigan, and the other night, it was snowing so bad, I could hardly see 5 ft in front of the car. Of course, being the junkie I am, I had my gps with me. I was locking the same, if not better than I do on a sunny day. So, I guess its all in the eye of the beholder.

 

[This message was edited by Thallas on February 23, 2003 at 08:30 AM.]

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