gps and high winds

[+johnnyuk]

I'm a newbie and was out geocaching with a Magellan Explorist . It was very, very windy and the skies were overcast and I was walking in Richmond near the Thames so it was a congested area that also had a lot of trees. Does this affect the satellite transmission? I could be standing in one spot and the distance to the cache could change within 10 feet (example, from 9 ft to 19 ft away) and I had not moved an inch. I did not have this problem the week before.

[+The Patrician]

Leaves, especially wet leaves, can affect the signal strength on the ground, the wind itself - no.

 

See http://www.gpsinformation.net/gpsclouds.htm

Edited June 1, 2011 by The Patrician

[team tisri]

I'm a newbie and was out geocaching with a Magellan Explorist . It was very, very windy and the skies were overcast and I was walking in Richmond near the Thames so it was a congested area that also had a lot of trees. Does this affect the satellite transmission? I could be standing in one spot and the distance to the cache could change within 10 feet (example, from 9 ft to 19 ft away) and I had not moved an inch. I did not have this problem the week before.

 

A shift of 10 feet like that is nothing overly unusual, all sorts of things can cause that.

 

Cloud cover can interfere with satellite signals. Heavy tree cover can do the same with an older unit. Being in a built-up area can play all sorts of havoc with a signal. I've personally seen my GPS give me a solid lock (claimed about 20-foot accuracy) but claimed I was about 1/4 mile away from where I really was (I know I was right and it was wrong because I was in town and could see the road signs, so knew exactly which junction I was standing at)

[+agentmancuso]

Wind is one of the few things that doesn't affect GPS signals. Except when it's strong enough to blow the GPSr off of the trig you're trying to take a reading for, which can be annoying.

[+drsolly]

Strong winds can blow one or more of the satellites off-course, but that wouldn't happen to all of them, and the satellites each measure the location of all the others, and send out signals to the manouvering jets to get them back on course. While this is happening, the off-course satellite adjusts its signal so that it seems to be coming from where it ought to be, rather than where it is, so GPS users won't notice any problems.

[+webscouter.]

Strong winds can blow one or more of the satellites off-course, but that wouldn't happen to all of them, and the satellites each measure the location of all the others, and send out signals to the manouvering jets to get them back on course. While this is happening, the off-course satellite adjusts its signal so that it seems to be coming from where it ought to be, rather than where it is, so GPS users won't notice any problems.

 

Really? Wind in space?

[+keehotee]

Strong winds can blow one or more of the satellites off-course, but that wouldn't happen to all of them, and the satellites each measure the location of all the others, and send out signals to the manouvering jets to get them back on course. While this is happening, the off-course satellite adjusts its signal so that it seems to be coming from where it ought to be, rather than where it is, so GPS users won't notice any problems.

:laughing:

 

Solar winds - obviously

Edited June 3, 2011 by keehotee

[+drsolly]

Strong winds can blow one or more of the satellites off-course, but that wouldn't happen to all of them, and the satellites each measure the location of all the others, and send out signals to the manouvering jets to get them back on course. While this is happening, the off-course satellite adjusts its signal so that it seems to be coming from where it ought to be, rather than where it is, so GPS users won't notice any problems.

 

Really? Wind in space?

 

You're an American. I can tell.

[+Kryten]

Strong winds can blow one or more of the satellites off-course, but that wouldn't happen to all of them, and the satellites each measure the location of all the others, and send out signals to the manouvering jets to get them back on course. While this is happening, the off-course satellite adjusts its signal so that it seems to be coming from where it ought to be, rather than where it is, so GPS users won't notice any problems.

 

Really? Wind in space?

 

You're an American. I can tell.

 

What complete and utter rubbish, the out of position satelites are nudged back into place by giant turtles.

[Ocean67]

Strong winds can blow one or more of the satellites off-course, but that wouldn't happen to all of them, and the satellites each measure the location of all the others, and send out signals to the manouvering jets to get them back on course. While this is happening, the off-course satellite adjusts its signal so that it seems to be coming from where it ought to be, rather than where it is, so GPS users won't notice any problems.

 

Really? Wind in space?

 

You're an American. I can tell.

 

What complete and utter rubbish, the out of position satelites are nudged back into place by giant turtles.

 

turtles? dont be silly, Ive seen the bloke in his hi-viz vest and a ladder re-setting them - and he looks nothing like a turtle.

[+drdick&vick]

you are all wrong, DrSolly probably has a computer program that can reset the satellite positions.

[+The Patrician]

Wind in space:

 

http://www.sciencemuseum.org.uk/onlinestuff/snot/what_would_happen_if_you_farted_in_a_space_suit.aspx

 

Nasty....

[+johnnyuk]

Thanks everyone - and for your sense of humor. I also read where I should hold the gps upright instead of horizontally like I was and that the Magellan Explorist GC is jumpy and when I get to within 70 feet or so, I should walk slowly. Does anyone carry a separate compass for coordinates?

[+drsolly]

you are all wrong, DrSolly probably has a computer program that can reset the satellite positions.

 

No, all it does is monkey with the signal so that your GPS thinks it's 20 meters from where it actually is.

[+drsolly]

Thanks everyone - and for your sense of humor. I also read where I should hold the gps upright instead of horizontally like I was and that the Magellan Explorist GC is jumpy and when I get to within 70 feet or so, I should walk slowly. Does anyone carry a separate compass for coordinates?

 

I carry a separate compass, but that's so I know which way is north without using the GPS, because the GPs can only orient itself if you start moving, and sometimes I'm keen to know before I move.

[+The Patrician]

Does anyone carry a separate compass for coordinates?

 

If I'm caching on a reasonably long walk I carry map and compass. I don't often refer to them now I've got OS maps on my GPS, but they have no batteries to run down or electronics to fail, which can be a comfort! Now the map can be a problem in the wind.....

[+Pharisee]

Does anyone carry a separate compass for coordinates?

 

I always carry a compass for the same reason as the good doctor but as yet, I haven't found a way of entering co-ordinates into it.

[+drsolly]

Does anyone carry a separate compass for coordinates?

 

I always carry a compass for the same reason as the good doctor but as yet, I haven't found a way of entering co-ordinates into it.

 

Use the RS-232 port.

[+Pharisee]

Does anyone carry a separate compass for coordinates?

 

I always carry a compass for the same reason as the good doctor but as yet, I haven't found a way of entering co-ordinates into it.

 

Use the RS-232 port.

 

Ahh... Why didn't I think of that.

 

[+abiherts]

Hmm that's my pc table Pharisee... but a much tidier one!

[+Amberel]

I also read where I should hold the gps upright instead of horizontally like I was ...

It's hard to give a generic answer because it depends on what sort of antenna is fitted to the unit, and in what plane it is mounted. Best thing is to find a spot with reasonable reception, switch to a screen that shows signal strengths, and try it out in various orientations.

 

... and that the Magellan Explorist GC is jumpy and when I get to within 70 feet or so, I should walk slowly.

It's very unlikely that the unit is more jumpy when you get within 70 feet, it's just that all units are jumpy to some degree all the time, but you are more likely to notice it when you are near the cache. The less good the signal, the more jumpy they might be, e.g. under tree cover, in a town with tall buildings around, etc.

 

The reason for moving more slowly as you approach a cache is that most units use some sort of rolling average in order to reduce the jumping around. This means the displayed position generally lags behind the actual position, and if you walk a little slower it lets the unit "catch up".

 

Does anyone carry a separate compass for coordinates?

A GPS receiver tells you where you are, not which direction you are pointing - if you are stationary it has no way of knowing that. If you are moving it can use a differential reading to compute your direction and speed of travel, but this is usually unreliable below about 3 or 4mph. Some units have a built in electronic compass, and this allows them to combine the information from the two sources in order to display direction even when you are stationary. The downside is that they may require occasional calibration, and they use a little more battery power. But it is very convenient for the direction to continue to function when you are stationary.

 

I carry a conventional compass in addition to the one in my Oregon, for the same reason that I also carry a paper map.

 

Rgds, Andy

[+TheAardvarkFamily]

I'm a newbie and was out geocaching with a Magellan Explorist . It was very, very windy and the skies were overcast and I was walking in Richmond near the Thames so it was a congested area that also had a lot of trees. Does this affect the satellite transmission? I could be standing in one spot and the distance to the cache could change within 10 feet (example, from 9 ft to 19 ft away) and I had not moved an inch. I did not have this problem the week before.

 

To try and add some sense to this thread!

 

Firstly, the GPS satellites are approx 26500 km from the earth so we'll gloss over the effect of wind!

 

The wavelength of GPS signals is approx 20cm on a frequency of 1575.42 MHz; i.e. pretty much headed into the microwave part of the spectrum. For an ideal signal you need line of sight to the satellites with no obstructions in between.

 

Leaves are very annoying to GPS receivers because they are potentially a great size for interferring with the signals (20cm or half wavelength is 10cm) and when nicely green and damp they have the potential to attenuate the signal significantly.

 

In the absence of a line of sight signal the receiver is likely to be receiving numerous signals from reflections off nearby objects (multi-path), this ambiguity of signal leads to the receiver having to pick a likely combination, one which will vary over time and hence lead to a varying in reported position.

 

In the extreme the receiver will lose lock on the necessary 4 satellites and potentially report a position as an extrapolation of where it was to try and be helpful... i.e. it will assume you are moving with constant velocity whilst it struggles to get another solution.

 

GPS Receivers are not all equal... some perform better than others under tree cover and multi-path... this is why I love my Garmin Forerunner 305.

 

Regards

MrAardvark

[+Lonetracker]

I find hurricane force winds really useful when using the GPS. I have it hung around my neck on a lanyard. When I am using it I have to hold it horizontal in front of me but when the wind is hurricane force, it does it for me and frees up both hands.

[+johnnyuk]

Wow! I'm learning a lot. Thanks so much. A map and a compass really seem to be necessary. You all are great!

 

JohnnyUK

[+Amberel]

Wow! I'm learning a lot. Thanks so much. A map and a compass really seem to be necessary.

Depends on what you mean by "necessary" Most of the time they aren't necessary, but can be useful. If you're out in the middle of the moors they are a good safety precaution.

 

Rgds, Andy