I'd been waiting most of the summer to see how heat shimmer affects measurements, and never once saw any. So I was quite surprised this morning, taking a 200' shot and it looked like I was in Death Valley. (Ok, a bit of hyperbole). Temperature was 19 degrees F, but bright sun on not too dark dead grass. I'm sure the ground was heating up and the relative temp/density of the air close to the ground compared to the air temp at about 5' above the ground caused it.
It seemed to screw up focus more than anything else, but if it's bad, will it change distance readings? Elevation readings?
> So I was quite surprised this morning, taking a 200' shot and it looked like I was in Death Valley. (Ok, a bit of hyperbole). Temperature was 19 degrees F, but bright sun on not too dark dead grass. I'm sure the ground was heating up and the relative temp/density of the air close to the ground compared to the air temp at about 5' above the ground caused it.
>
> It seemed to screw up focus more than anything else, but if it's bad, will it change distance readings? Elevation readings?
I'd expect that it depends upon what the target looks like through the telescope. If the target is steady, but blurred, probably the main effect is on zenith angles. If the target image is dancing from side to side and up and down erratically, both horizontal angles and zenith angles should be significantly worse than under good conditions.
One way to deal with this problem is to find ways to raise the line of sight as far above the ground as possible. Raising the target is one thing to test. The best plan for the most careful work is to pick a different time of day.
Yes. This can happen anytime there is a significant temperature change occurring. In my part of the world this is all to frequent. Move to an area of minimal normal daily temperature change to minimize the opportunity for this to happen. Something like within five miles of one of the Great Lakes. The gigantic thermal sink the lake provides has a moderating effect on temperature changes. I recall a period one winter in Michigan where the air temperature was 4 F for two weeks. Morning, noon or middle of the night.
How about when your using (if equipped on your ts) what leica calls atr auto target recognition. You know just having the inst. find center on the prism. If im dealing with really bad heat waves we call them, i always assumed that it had to be better than trying to manually sight in a blurry target.
Anybody know if heat shimmer has any affect at all utilizing this method. Course if your traving with a robot and the fore sighting the rod you really have now choose in the matter.
A simple check of that would be to rotate the TS and resight the prism several times. See if you get virtually identical results or sloppy results. Then you will know if the atr is helping.
Good question. Visible light is refracted by radiant shimmer while the infra-red spectrum is not affected nearly as bad. Most of the EDM equipment utilizes infra-red. If the equipment uses the infra-red to center on the optimum signal reflection, it could be better to use that than a human eyeball.
Something to check out, for sure.
Very astute Paden.
The ~620-680nm wavelength laser on that EDM cares not one tittle for convective refraction.
It is only we lowly I-men who suffer this genetic shortcoming. We must do more breeding in the deserts.B-)