Message in a bottle gets climbers rescued (Amazing)

The Oregonian ^ | January 16, 2008 | STUART TOMLINSON

[Squidpup]

I just got a gps last spring and had fun geochaching with my family this last summer. Picked up a traveling bug I need to plant somewhere else, pronto.

[William Tell]

From the article: "They had neither a GPS unit nor a mountain locator unit, which Rollins said was a mistake."

Just on the off chance that we might need it, I carried a simple GPS on a car trip up the Oregon coast just after that very bad storm in early December. We also had a cell phone, a two-meter ham handheld, and a fifty-watt capable two-meter ham mobile transceiver. We might have gotten stranded but I was pretty confident that I could summon help and tell them where we were.

[ikka]

I doubt very much that their cell phones don't have GPS on a 911 call. I don't think they even sell them without it anymore.

OK, I will have a stab at it.

Cell-phone based geolocation uses triangulation based on the cell phone being able to be seen by more than one cell tower. They are accurate in places like a city, to within 50 or 100 feet.

In such a remote area, there would not be the overlap of cell towers needed to triangulate the position. GPS is a different beast, uses satellites in orbit, and is accurate down to about 3 feet or less.

[Captain Rhino]

No, you can get something like an approximate triangulation on a cell phone’s location by analyzing the arrival time of signals at cell phone towers in the area PROVIDED there is more than one. With two, the fix is not so good. Three or more will give you an approximate location. The location is only approximate since the difference between the signal arrival times can only be measured so precisely (we’re talking of differences in the hundredth of a second or less here) and there is atmospheric distortion to signal travel times that has to be considered as well. This may seem like GPS but it is not even close to its precision. Further, while there are obviously cell phone relay towers in the area (that how the calls went back and forth), they are probably somewhat dispersed due to the terrain and there may not have been enough towers or the overlapping coverage areas needed to do the triangulation as described above.

A cellphone doesn’t have a GPS receiver (for picking up location signals from GPS satellites) unless it is specifically built into the telephone. Adding GPS usually adds significantly to the cellphone’s cost. Further, a GPS receiver doesn't emit a signal (to triangulate on), it just receives ones that are already in the air and computes its location using timing differences from the multiple satellites it “sees” overhead. GPS is superior to the cellphone triangulation method because the likelihood of getting three or more GPS satellite signals is very high due to the extensive coverage in geosynchronous orbits around the Earth and because the calculation algorithm used in determining location is fairly precise.

Pitt said their cellphones didn’t have the GPS capability. Since he was one of the two lost hikers, maybe you should believe him.

[Kevmo]

Cool. Geekiness saves lives.

[Reeses]

GPS satellite signals is very high due to the extensive coverage in geosynchronous orbits around the Earth

GPS satellites are not in geosynchronous orbits, they are in low Earth polar orbits, and their accuracy is not as good as triangulating from cell towers can potentially be. A few years ago a special geosynchronous WAAS satellite was added that sends out a correction signal. This information is computed by land stations that know their exact location and compare it to their GPS calculated location, which is usually in error. The gravity of the Earth is not uniform and the GPS satellite positions vary constantly from their predicted positions.

Rather than just timing signals a system could be implemented to measure the phase of a radio wave when it hits. This would improve the accuracy down to a tiny fraction of an inch. Some very precise surveying equipment uses this technique.

[Captain Rhino]

Thanks for correcting me on that. I was thinking of television and radio communications satellites which are in geosychronous orbits.

[Hot Tabasco]

Message in a bottle

The last message I ever got from a bottle said "you're the disco king, ask her to dance..."

[blam]

Message In A Bottle