GPS affected by snow?
Fly Conventional Gear
Thread Starter
Join Date: May 2007
Location: Winchester
Posts: 1,600
Likes: 0
Received 0 Likes
on
0 Posts
GPS affected by snow?
I'm sure I heard on the news recently with all the snow that drivers were finding their sat navs stopped working when it got very heavy.
I was very surprised to here this - I had always assumed that the frequency that GPS operates on, aprox 1200MHz and 1575MHz if I recall, should not be affected by/reflect off precipitation of any sort. Is this the case though? Could really large snow flakes in the air disturb the signal?
I wondered if perhaps it was physical snow accumulations on the car itself that were causing the signal to be lost.
I was very surprised to here this - I had always assumed that the frequency that GPS operates on, aprox 1200MHz and 1575MHz if I recall, should not be affected by/reflect off precipitation of any sort. Is this the case though? Could really large snow flakes in the air disturb the signal?
I wondered if perhaps it was physical snow accumulations on the car itself that were causing the signal to be lost.
Last edited by Contacttower; 24th Jan 2013 at 10:07.
Join Date: Jun 2001
Location: Chicago, IL, USA
Posts: 518
Likes: 0
Received 0 Likes
on
0 Posts
I don't mean to be sarcastic, but wouldn't your question be better suited on a CAR forum?
I mean, airplanes use wheels and brakes too, but if my expensive BMW (yeah, right!) isn't braking properly I'm surely not going to ask around here for advice!
I mean, airplanes use wheels and brakes too, but if my expensive BMW (yeah, right!) isn't braking properly I'm surely not going to ask around here for advice!
Join Date: Nov 2002
Location: the pub
Age: 57
Posts: 149
Likes: 0
Received 0 Likes
on
0 Posts
From what I remember of Radio theory, higher frequencies suffer more attenuation than lower ones. Why this should be worse with snow than rain I haven't a clue.
Try and ignore people with nothing better to do than make (to themselves at least) clever remarks.
Try and ignore people with nothing better to do than make (to themselves at least) clever remarks.
Join Date: Oct 2009
Location: Close to you
Posts: 250
Likes: 0
Received 0 Likes
on
0 Posts
That the signals are not effected by atmospheric conditions is not true.
How does your weather radar work? By reflection of precipitation, right?
In the GPS we have two channels. One the L1 is used for civil use.
So why two channels?
The L1 contains the Precision code and the C/A (which is for civil use).
Both codes contains a model of the atmosphere. But the C/A time code is dithered to degrade the accuracy.
Anyways. The Military will use the L1 and the L2.
The L1 and L2 contains both the Precision code.
Since the channels have different frequencies the refraction in the atmosphere will be different. So the two P-codes will arrive at the receiver at different times. Because of the propagation in the atmosphere.
So the UHF band is affected by precipitation to some extent.
But that the receiver will stop working all together is something I have not heard of..
How does your weather radar work? By reflection of precipitation, right?
In the GPS we have two channels. One the L1 is used for civil use.
So why two channels?
The L1 contains the Precision code and the C/A (which is for civil use).
Both codes contains a model of the atmosphere. But the C/A time code is dithered to degrade the accuracy.
Anyways. The Military will use the L1 and the L2.
The L1 and L2 contains both the Precision code.
Since the channels have different frequencies the refraction in the atmosphere will be different. So the two P-codes will arrive at the receiver at different times. Because of the propagation in the atmosphere.
So the UHF band is affected by precipitation to some extent.
But that the receiver will stop working all together is something I have not heard of..
Join Date: Oct 2009
Location: Close to you
Posts: 250
Likes: 0
Received 0 Likes
on
0 Posts
one dot right: You are correct about your statement.
frequencies around 10GHz are very much affected by precipitation. Hence, this frequency is used in weather radars. The attenuation can be as much as 1dB/km!
Snow also affect frequencies around 10GHz but not as much as rain.
Snow will have greatest attenuation around 30GHz
frequencies around 10GHz are very much affected by precipitation. Hence, this frequency is used in weather radars. The attenuation can be as much as 1dB/km!
Snow also affect frequencies around 10GHz but not as much as rain.
Snow will have greatest attenuation around 30GHz
Fly Conventional Gear
Thread Starter
Join Date: May 2007
Location: Winchester
Posts: 1,600
Likes: 0
Received 0 Likes
on
0 Posts
I mean, airplanes use wheels and brakes too, but if my expensive BMW (yeah, right!) isn't braking properly I'm surely not going to ask around here for advice!
I guess I could have left out the car reference to be honest and just asked 'can GPS be affected by snow?' It's a legitimate question that has relevance to aviation.
Fly Conventional Gear
Thread Starter
Join Date: May 2007
Location: Winchester
Posts: 1,600
Likes: 0
Received 0 Likes
on
0 Posts
Snow will have greatest attenuation around 30GHz
Join Date: Jul 2008
Location: Skating away on the thin ice of a new day.
Posts: 1,116
Received 14 Likes
on
8 Posts
You put enough of anything between the tx and rx antennae and you will lose your signal.
The satellites put out pretty low power (50 watts according to online source)
From an online GPS info blurb..
Due to their high frequency, GPS signals cannot permeate stone or water. Even a thick foliation in forests may attenuate the signal to an extent that some (mainly older) GPS receivers have difficulties in receiving the signal. However, GPS works in any weather including a thick cloud cover. Problems may only arise in very heavy snowfall.
The satellites put out pretty low power (50 watts according to online source)
From an online GPS info blurb..
Due to their high frequency, GPS signals cannot permeate stone or water. Even a thick foliation in forests may attenuate the signal to an extent that some (mainly older) GPS receivers have difficulties in receiving the signal. However, GPS works in any weather including a thick cloud cover. Problems may only arise in very heavy snowfall.
Join Date: Mar 2011
Location: Milano
Age: 53
Posts: 460
Likes: 0
Received 0 Likes
on
0 Posts
The L1 contains the Precision code and the C/A (which is for civil use).
Both codes contains a model of the atmosphere. But the C/A time code is dithered to degrade the accuracy.
Both codes contains a model of the atmosphere. But the C/A time code is dithered to degrade the accuracy.
Join Date: Mar 2011
Location: Milano
Age: 53
Posts: 460
Likes: 0
Received 0 Likes
on
0 Posts
From what I remember of Radio theory, higher frequencies suffer more attenuation than lower ones. Why this should be worse with snow than rain I haven't a clue
Ciao,
Dg800
Your information is a bit out of date. The Commander in Chief put an end to that in 2000.
And your source is?
GNSS Frequently Asked Questions - GPS:-
Last edited by Groundloop; 25th Jan 2013 at 13:32.
Join Date: Feb 2000
Location: Alaska, PNG, etc.
Age: 60
Posts: 1,550
Likes: 0
Received 0 Likes
on
0 Posts
Ground loop is correct. I also spent a lot of time both teaching GPS applications and using it in the field for precise surveying. Selective availability and C/A code are 2 different things Selective availability has indeed gone away, but Civilian receivers still use the C/A code for positioning which is less accurate that the encrypted code available to the military.
Join Date: Feb 2008
Location: USA
Posts: 93
Likes: 0
Received 0 Likes
on
0 Posts
Just to be clear about this, "Less accurate" and "deliberately degraded" are not the same thing. L1 C/A is at this point is running at it's full potential accuracy. It's true to say it provides less accuracy than the L1 and L2 P(Y) codes (and the newer SPS and PPS signals), but that is by design, not because it's being "degraded".
Oh and to the original question, attenuation and scattering due to (falling) atmospheric precipitation should have a negligible effect on the GPS link budget. However significant deposits on the antenna radome could indeed have a debilitating effect.
Oh and to the original question, attenuation and scattering due to (falling) atmospheric precipitation should have a negligible effect on the GPS link budget. However significant deposits on the antenna radome could indeed have a debilitating effect.
Last edited by ion_berkley; 27th Jan 2013 at 07:33.
Join Date: Mar 2011
Location: Milano
Age: 53
Posts: 460
Likes: 0
Received 0 Likes
on
0 Posts
Just to be clear about this, "Less accurate" and "deliberately degraded" are not the same thing.
Ciao,
Dg800