Weather Effects

[+IGJoe]

Granted that I am new to this and I'm still getting used to the hobby and my (GPS) unit I was wondering how much interference I should expect from cloud cover.

Will a cloudy and foggy day significantly affect my GPS accuracy?

 

I was trying to find a cache today (a cloudy, foggy, misty day) and my readings were all over the place. I am curious if I should wait for better weather (if so how does anyone in Seattle do this?) or dig a little deeper into my user's manual.

Edited January 3, 2006 by IGJoe

[+Team Cotati]

Granted that I am new to this and I'm still getting used to the hobby and my (GPS) unit I was wondering how much interference I should expect from cloud cover.

Will a cloudy and foggy day significantly affect my GPS accuracy?

 

I was trying to find a cache today (a cloudy, foggy, misty day) and my readings were all over the place. I am curious if I should wait for better weather (if so how does anyone in Seattle do this?) or dig a little deeper into my user's manual.

From Magellan's www site: "The GPS 315 gets a precision fix on your exact location, even in heavy cloud cover, by tracking up to 12 GPS satellites simultaneously. Equipped with a super sensitive quadrifilar antenna designed for fast satellite signal locking, the GPS 315 is accurate to within 15 meters or better."

 

I would expect the same or better to be true for other models from this vendor and others.

Edited January 3, 2006 by Team Cotati

[+Kai Team]

I was trying to find a cache today (a cloudy, foggy, misty day) and my readings were all over the place.

Weather will effect your reception a little, but it's more likely that you're suffering from the "Drunken Bee Dance".

 

The GPS knows your position but can't tell which way you're facing unless you're moving (it compares your current position to the last position and assumes that you're facing in the direction of movement). When you stop (or slow way down), the navigation needle starts to flip around randomly because it doesn't know which direction you're moving in or which way you're facing.

 

If your GPSr has a built in electronic compass (e.g. Garmin Vista or 60CS) built in, turn it on and set it to activate below your normal walking speed (e.g. 2 mph).

 

If your GPSr doesn't have a compass, check the distance and bearing (direction to the cache) as you're approaching the cache and moving at a good walking pace. Use a separate compass to follow that bearing, or sight an object along that bearing at roughly the right distance. When you get close, ignore the GPSr and use your geosense!

[+EraSeek]

No. Virtually no effect. The GPS frequency signal was chosen specifically so as not to be affected by these factors. I live in Seattle. :

 

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

 

5) Ok then, can I use my GPS underwater?

Answer: No. Just a few millimeters of "solid" water will severely attenuate the GPS signal.

 

Joe Mehaffey

[+Alan2]

Wait for Spring. Foliage is the problem not clouds.

[dsandbro]

I'm a geo-wimp. Bad weather makes me stay inside and not go geocaching, so, yes, rain affects my locating ability.

[+Lizooki]

Your GPSr is nothing more than a use-specific radio reciever...hence gpsR(eciever). Radio signals can and are affected by weather, sunspots & other solar activity, radio interferance in the area, and the actual geologic make up of the area you are in. No matter what the frequency is!

 

That said, the GPSr's seem to bothered less by all of these.....but I have seen days when reception was poor on my Amateur Radio equipment and the GPSr was accurate to w/ in a state or so....

 

If you're interested, go pick up an ARRL Amateur Radio handbook at the library and read.....the gov't uses it for reference material.

 

Matt-

 

btw- the above stated reasons are why the US Coast Guard and other military agencies are establishing the land use towers.....to improve accurracey.

[+Prime Suspect]

The GPS signal frequency of about 1575mhz was chosen expressly because it is a "window" in the weather as far as signal propagation is concerned.