Hello,
I was wondering what rod height most surveyors use for static surveys. When I look at photos the rod appears to be at 2m or higher. Is there a reason for that?
I always check the plumb of the rods I use. For static observations I use a fixed height tri-pod with rod. My thought is to keep the rod height low (1.5m) to remove any tilt there might be. The level bubbles are only so accurate and the higher the rod height the more the horizontal could be off.?ÿ
Does the 2m or higher help with multi-pathing or something? I am tall and always wondered if my head interrupts the received signal?
Thanks,
Dan
A big reason for the predominant 2m rod height is the NGS requirement/preference of fixed-height rods for any observations that will be part of an IDB/NSRS submittal, such as a height mod or FAA project. The industry standard for fixed-height rods is 2 meters.
For any decent tripod with calibrated bubble, the difference in tilt error is pretty minimal between 1.5m and 2m. Satellite visibility shouldn't be much of an issue either unless there is regular interference with the signals, like large trucks passing by a receiver on the side of the road. Even then, 2m vs 1.5m probably won't make or break a session. Sure, your head might interrupt the signal but unless you are standing next to the receiver for the duration of the session it shouldn't be a problem. Multipath is more of a function of the surrounding area than the height of the antenna - if you're getting multipath with 1.5m, you're probably getting multipath with 2m.
In my experience, the 1.5m setting for the Seco fixed-heights seems to be more stable, especially in areas with poor ground stability and/or high winds. So that is what I prefer, but for NGS projects I use 2m for consistency and ease of submission.
No matter what height you are using, if you sandbag those suckers well they are unlikely to move.
I think you've nailed the tradeoff: low slightly reduces out-of-plumb and high can reduce multipath in some situations.
If your head is in the way for the duration of the measurement, I'd opt for the taller rod.
Calculate how far off you are horizontally.?ÿ At say 20 minutes and 2 meters 1.2?ÿ cm horizontally. At 1.5 meter and 20 minutes 0.9 cm.?ÿ So you aren't gaining a lot by shortening.?ÿ If those values are significant, invest in a more sensitive bubble.
Consistent rod height helps to reduce blunders.
The 2 meter rods are used to keep the HI constant. I've never liked them cause they are awkward.
When I did have them HI's were somewhat irrelevant since I didn't gather elevations with GPS for anything but very rough surveying.?ÿ
Then Geoid models became more and more refined and over time HI's for GPS have become more important since the elevations are so much better.?ÿ
Stil, I like my graduated rods for locations and tripods/optical plummets for control points.?ÿ
But the 2 meter rods are popular as they eliminate a reason to worry about measure ups.?ÿ
You need to pay more attention and spend more time measuring your set-ups while a 2 meter guy will not.?ÿ
Also newer antennas do not suffer from the same ground interference as the older ones do.
Newer units can be closer to the ground without worry. If you are using a L1/L2 Trimble antenna, higher up is better.?ÿ
For static I'm going to want to put the thing on a tripod/tribrach anyway. I don't see much to gain, and something to lose, by using a 2m rod.?ÿ