Re: How far can GPS signals penetrate?

J Wexler <J.Wexler@xxxxxxxx> wrote:
> Experience tells me that GPS signals don't penetrate much. Under a
> canopy of trees - the inside of my pocket - inside a plane (unless close
> to a window) - there are lots of places where my handheld GPS won't
> work.

The signals will not penetrate metals or very small amounts of water.

> The other day I took a flight from Edinburgh to Gatwick, and watched our
> route on my GPS. Before final approach, I switched it off and put it
> back in my briefcase. I got off the plane and into the terminal, collected
> my baggage, walked through the building, get in a car, and was driven
> some twenty miles to my final destination. When I unpacked my case
> later, I found that the GPS had in fact been running all the time, and
> had tracked the car journey quite accurately - certainly too well to be
> dead reckoning. I was very surprised. Should I have been?

Well, the briefcase (assuming most non-metal materials) won't block
much. The inside of most passenger cars works pretty well. While the
roof is metal, most windows have a significant pitch so that much larger
portions of the sky can be seen directly. The angles and sizes make it
much better than a commercial aircraft with tiny, vertical windows.
With a good distribution of satellites for your location at the time,
this isn't unexpected at all. If you've got 9 or more, it doesn't take
much visibility to be able to track 4 of them. If you only had 5 or 6
visible, then it might have been much more difficult.

Many times when my ancient Lowrance Airnav 100 falls on the floor under
the passenger dash, it will have no problems remaining locked.

--
Darren Dunham ddunham@xxxxxxxx
Senior Technical Consultant TAOS http://www.taos.com/
Got some Dr Pepper? San Francisco, CA bay area
< This line left intentionally blank to confuse you. >
.

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