I want to measure a distance (approximately 700 feet) with the survey instuments between two GPS data points across a pond. It is possible that the distance will be in error because of the atmospheric conditions of the pond. It may be significant. Is there a way to minimize the anticipated error?
Should I use more prisms, measure at a certain time of day or will all that be useless.
I am also going to traverse a land route to compare the results.
I remember trying to measure a short distance across a swift river. We had to traverse a land route because the distances we got across the river were never consistent.
Why not set up a baseline on one side and triangulate to the point across the river as a check. Do this at night if possible. You could do this simultaneously with a few total stations. Possibly do the reciprocal from other side .
That's a good idea. Thank you.
Since you can see between the points you could also set up points parallel to the line and perform the above @pfirmst stated as well. Sorry I am down in my back so not thinking clearly. But performing reciprocal observation at same time could achieve the results.
pfirmst... Not trying to determine elevation.
I'm suprised you experienced a problem with distance across a river previously. I could understand significant refraction that would cause a pointing error and a problem with the vertical. I find it hard to believe that a change in the density of air over a pond would be so great as to have a meaningful effect on the distance your instrument would register. I haven't run the numbers to calculate the possible parts per million change based on an extreme dry air outside of the pond and an extreme humid air over the pond but off the cuff I don't think they are meaningful but for the extremely precise projects.
Thank you.
Could it be moisture in the air? Anyway I am trying a land route to discover if there is an error.
It wasn't just one day with the river. We tried several times and never got consistency.
Where you shooting to a 360 prism or a regular prism. Also what was the sun doing on the water at time of shooting the distance that was not repeatable. I have seen funny things when sun is aligned either with or behind the prism and or total stations over my career EDM’s act funny. Also when low so not far above water line . You could also paddle out to the middle and do a wet and dry bulb readings about the half way mark. Just to see what difference you have. Oh my mind is not allowing everything to get out correctly I am sure. A bit spacey today. You have options so you can determine what’s possibly going on.
Refraction affects levelling and total station measurements the same way.
Air layers are horizontal, these cause refraction that affects vertical angles.
Setup two total stations, one on each side, shoot each position in short succession.
