This whole fiasco could have been avoided. Our original plan was to occupy the pedestal in the hut that their instrument now occupies. We planned to establish the position on the pedestal and on the prisms to be monitored. BUT, they decided to try to do it themselves and have us just check their work. So, here we are trying to make sense of non-sense. We sent them a report stating such and we will see where it goes from here.
Well that was kinda my point....
Unless BOTH instruments (theirs and yours) have been checked on the calibration Base Line, then you ARE [possibly] comparing apples and oranges.
Sounds like your instruments are SOLID (and recently tested), what about "their" instrument????
Loyal
Monitoring
I think the best way to resolve this is to check the prisms from the outside pedistal, and compute the difference between your positions and the contractors positions, for the same epoch. Then come back and remeasure all the points that you measured the first time, and use the differences between your two surveys to estimate the values that the contractors equipment should provide, and compare that estimated value to the values that the contractors equipment is providing. i would consider runnning your instrument across a calibration baseline before each survey, and trying to get nearly the same weather conditions for the check surveys. Also correct for temperature and pressure. I would also use the same thermometer and barometer for both surveys. I would also check the barometer and therometer before each survey. This sounds like an interesting project.:-)
good thread. I like a lot of the thoughts above. including considering a window of sorts. I think it would be great to experiment with shooting through glass over time as well. (do it through the window and with the window open; and do that during different seasons of the year to see if there is a significant change through glass, and if that difference changes in different conditions).
Using a calibration baseline is not necessarily 'apples to oranges'. One great use of a calibration baseline is to compare the same instrument before, after, and often at certain time intervals through a job. That is the same analogous "apple to apple". I would use the same baseline every time as well. One where you have confidence in the stability of the monuments.
Of course it sounds like you might have a hard time convincing them to re-install a window.
By the way, would you take your temperatures inside the building at the gun, outside the building and again at the target? I am thinking your distance measurement is mainly through the outside temperatures and you would measure outside near the building as well as at the target and average those for you ppms. (?) or do you even measure temperatures?
You want the total effect of temperature over the optical path. If you want to do it to the ultimate, you break the distance into inside and outside parts and compute a correction distance for each.
In this case most of it is outside, so that will dominate. You can probably set the outside temperature on the instrument and neglect the very short inside part, since even 100 ppm times a couple feet is still negligible.
