In one area where I work, there are a lot of transmission lines. We use these for traversing as you can imagine it saves a lot of time cutting brush. I was wondering though if these transmission lines would have any ill effects on GPS data. I'm kinda' new to GPS so any advice,/response would be appreciated.

S S

We have used transmission line R.O.W. for windows on many occassions. I.m sure it is possible to suffer some multipath from the lines themselves, although I'd doubt it would be on a large enough scale to even be seen, in most cases. What I would be most concerned about are the poles, or towers, whichever type structures are involved. That could be a major source of SV blocking and/or multipath. As for electrical disturbance, I've heard yes and no. I tend to think probably no on that.

Probably depends are how high of voltage and how much EMF is in the air. I distinctly remember having problems with some older gear (1994) under a high tension line. Not sure the GPS signal was affected, but the data display on the LCD screen was just garbage from all of the EMF. I think if it works OK, you are probably all right. I don't worry too much about the actual wires causing much problem or the structures unless you are real close, usually try to be mid span.

Shelby

Put one receiver where it has a really clear view of the sky and no excuse for bad data.

Put one receiver in your typical choice for a spot in the power line right-of-way.

Process the data in Ashtech Solutions.

Look at the raw data plots.

Did the one under the power lines do as well as the one under a blue sky.

I agree with J.D. I would sweat the poles or the towers much more than the wires or the EMI. The trees at the edge of the R/W are probably more of a problem than the wires.

But the proof, as usual, is in the dirt.

You may be new at this GPS stuff, SS, but you won't be the first guy who wanted to use that cleared line for this purpose. For most of us it has worked.

Had to "run in an elevation" for another crew, and of course the control point for the optical work they had already done was in the center of a 4 way crossing of transmission lines at a substation. Worked like a champ.
I'd be more concerned about frying your TDS or SMI ram card in the same scenario, as they have very little if no shielding and they will fry. Don't ask me how I know.

Thanks for the info guys. I didn't know that about the ram cards. I have had my 48 give me some funky data when the solar flares were real active though.

A post on the Ashtech board by Edward Rogers on 8/7/2001 regarding this topic was quite enlightening and eye-opening.

Click on this link to view it:

GPS in High Voltage Corridors



Modified By Scott Partridge on 7/30/2002 at 1:56 PM

thanks for linking that post. I vaguely remembered reading it, but in the context of the current thread I had forgotten the "cautions/warnings" that were given on the very high voltage lines. I wouldn't doubt for a second that the super charged lines can EMF a circuit board. Back a few short years ago when I had more time to bass fish, one lake we spent a good deal of time on was a typical East Texas "power plant lake". Lots of very high voltage stuff coming out of the p plant. One of the mains that left the plant towards the Dallas area crossed right over one of our favorite fishing holes, and the lines had to be 60-80 feet above the lake. With a 7 foot graphite rod in the air you could feel a constant "buzz" as well as hear an occassional "crackle" between your hand and the rod handle. Now that would have to have an effect on GPS signal as well as possibly an adverse effect on the hardware.

I just wasn't thinking about the super charged lines.

If walking under the power line with a range pole makes your fingers tingle that is probably not a good spot for a GPS receiver or you either.

I have also been told not to work in the railroad right-of-way, the highway right-of-way, and in environmental hot zones.

Pulling the lid off a manhole and measuring a ring down is confined space entry according to OSHA.

Surveyors are always going where they have no business going. But safety should always be a big consideration.

Phil wrote:

Pulling the lid off a manhole and measuring a ring down is confined space entry according to OSHA.


OSHA's getting a bad rap on this one. A manhole may be a confined space, but entry is another matter:

"Entry means the action by which a person passes through an opening to a permit-required confined space. Entry includes ensuing work activities in that space and is considered to have occurred as soon as any part of the entrant's body breaks the plane of an opening to the space."

Popping the lid and dropping a rod down into a manhole doesn't consitute confined space entry.

Call it a bad rap if you want to. OSHA fined a business because somebody fell in a manhole.

The ruling was that because the lid was removed the risk of confined space entry should have been anticipated and planned for.

If you fine somebody for non-compliance then, to me, that says ring downs are confined space entry. It's not about whether I agree with that. It's about the money.