2 dead on Barkley

[artcarney_agr]

I know just what you mean MASBASS. I've used Trimble's GPS units for mapping and setting reference points on site surveys. Like you said, vertical obstructions affect GPS performance. Running a boat under a bridge is a quick way for a satellite to lose signal with your receiver. I'm not sure of the exact location of the accident, but I know there is a bridge in Little River in the area of the accident. Do you think it's possible he went under the bridge, lost signal, and before it came back online he ran into the rock wall? The tall vertical wall with trees on it may have also blocked the satellite signal.

I also remember from surveying class that there is a time of day when there is only a few of the satellites visible in the sky due to the earth's rotation. Could it be that at around midnight the number of visible satellites was at a minimum?

[kc]

The accident happened near the mouth of little river. In fact I believe he hit the rock island between the river channel and the mouth. You have to come in at an angle between the smaller island and the bigger rock island to follow the channel and that is a little tricky in the dark. GPS is not for blind navigation. I have used it in heavy fog to cross the lake (idling) and it worked fairly well but the whole time I was holding my breath thinking that someone else might run over me.

kc

[artcarney_agr]

It looks like the boat was recovered from the rock wall where the house sits on top of it that has a cannon on the point and a swimming pool. It was a pretty boat, a new looking red and white Stratos 201 Pro XL.

[Danny]

I'm confused by the statement about the statelites being out of view. I always thought the satellites were in geosynchriness orbit. Is that not right?

And please forgive my poor spelling. My dog seems to think she needs to be in my lap while I'm typing. LOL\

At least someone loves me, besides my wife.

Danny

[MASBASS]

Sorry about that, when I said out of view we mean that either the are blocked from direct line of sight or their rise and set times make them out of view from the reciever. You get your best positions when you have several and they are spread out, most of the time on a boat you block a portion of the by windshield or your person and make the unit less accurate.

[tracy]

I feel bad for happened to these people and for what their families are going though. But i don't understand why people are using thier GPS to blindly navigate.


every GPS unit that i've ever used has a warning telling us not to do this.

maybe that warning is on there for a reason?????????????

[SpotBoy]

[font size="1" color="#FF0000"]LAST EDITED ON Jun-28-06 AT 11:59AM (EST)[/font][p][font size="1" color="#FF0000"]LAST EDITED ON Jun-28-06 AT 11:58*AM (EST)[/font]

Hey this sounds like another GOOD point for using head lights !! I bet they would have seen that wall before they hit it ??? Yea some argue that it blinds them. BUT that blindness (if it happens) is only temporary. DEATH is permanent

[artcarney_agr]

I agree SpotBoy!

[artcarney_agr]

Danny,

Here's a clip that I cut from an article on Satellites and GPS navigation that should answer your question:

.....The last major issue was the altitude of the GPS satellite constellation. Satellites are generally either placed in low Earth orbit, a few hundred kilometers high, or in geostationary orbit over the equator, 36,000 kilometers high, where they take 24 hours to orbit the Earth and remain in a fixed position relative to the Earth as it turns under them.

Putting the satellites into low Earth orbit would reduce the size and cost of the boosters required to launch them, and would also reduce the power required for the transmitters on the satellites. However, obtaining adequate coverage would demand a large number of satellites. Putting them into geosynchronous orbit would reduce the number of satellites, but it would require more powerful launchers and transmitters, and it would not provide good coverage of the polar regions.

The altitude finally chosen was a compromise: a circular orbit with an altitude of 20,200 kilometers and a period of 12 hours. At that altitude, 17 satellites would be enough to make sure that four of them, the minimum number needed to establish a position, would always be visible from any location on the Earth's surface.

The GPS constellation finally implemented actually has 24 satellites, consisting of 21 in active operation, plus three spares. The 24 satellites operate in six different orbital "planes" (an orbital path shared by multiple satellites), with four satellites in each plane. The planes are inclined 55 degrees with respect to the equator. The GPS satellites are also fitted with nuclear blast detectors as a secondary mission, replacing the early "Vela" nuclear blast surveillance satellites in this role.

[Danny]

Hey Scott, that was some great reading. To prevent my searching, can I take a short cut and ask you the URL to that site? I'd love to read more.

Thanks,

Danny

[artcarney_agr]

Ask and you shall receive!



http://www.faqs.org/docs/air/ttgps.html

[MASBASS]

A bridge would only cause a few seconds problem, a vertical wall could very easily be a major problem. You not only take 40%-50% of possible sky you also create a Multi-path problem. Multi- path thinks the unit is still locked in good position but in fact the fraction of a second delay in the signal can cause major position error. 50-100 feet easy. There is no way to know for sure. I just know that there are several possible problems and all but one is human created, solar flares can cause some major problems. The only time I had problems with weather conditions one time it was when I had about 4" of snow on my antenna. It is terrible about the accident, that is why IMO anyone would be extrememly foolish to navigate in our lakes around here using only GPS or relying soley on them, there are too many factors that can cause problems. The biggest factor being human involvement. How they work is an exact science how people use them is not.