Need Some Advice ''Temperature Correction''

The corrections are dependent on the wave length of the carrier signal. Your manual SHOULD have the wave length AND necessary equations.

Infrared, near infrared, helium-neon LASER, etc. etc. are somewhat different.

Loyal

I assume that would work as long as the shots at 35 and 85 to come up with a correction factor were taken under the same conditions and temperature as when the work was done

ric

I didn't really read the end of your post very well Paul...

How would “I” do it?

I would write a program to query the raw data file, extract all of the observed SLOPE distances, compute the “0ppm” distance using the incorrect temp/pressure (and correct equation). Then I would recompute the SLOPE distance using the same equation and the RIGHT temp/pressure. Of course you would have to recompute the HD/VD values as well.

I have had to do this in the past for the same reasons that you gave...(old-timers disease).

Loyal

Other factors would be negated, doing at the same time, the difference should be only in the temperature correction.

I only readjust when the settings move sufficiently from the previous settings. I work around an anticipated range for the day. Changing during the day is rare. What bugs me is that I missread the 8 for several days observations on this project.

Since this is only distance, my adjustment will be made in Carlson Survey holding the traverse point I began on yesterday, I store my backsight shots. As I extend my traverse in 3 other directions I will reobserve several other traverse lines. The adjustment point is not critical as my overall control will be GPSed, 8 to 10 static observations. P.Q. boundaries to be in agreement with several filed map adjoiners or near adjoiners, state highway, active railroad and stream. There will be 3 lot line agreements with residential lots, 2 are exceptions, the third having a ancient description along the vacated? alignment of the relocated state highway. The parcel originally went to the old state highway to the North (which my father and I at one time owned) and the relocated state highway cut off from the balance. The 2 exception parcels (2 tracts in each) are mostly monumented but descriptions are not in total agreement.

The old state highway crossed the new state highway and South of the state highway, it and the 3 arch stream bridge were abandoned, they are calls for the ancient residential description. Yesterday I stopped at the residence on the West side of the stream to ask landowner permission to access the abandoned bridge area. Well after an hour of looking over his shoulder as he went through internet research he had done on local railroads, trollies, bridges and the cement mill formerly on the PQ, we discussed his deed, 3 parcels and the abandoned road right of way clearly missing by the geometry. Looks like another survey down the road. Only mere remnants of 2 stream side arches are visible. The adjacent residential parcel is a converted mill and quite interesting. Three lines can eventually be agreed on between it and the PQ, with 2 lines common to said residential lot across the stream. Separate agreement required.

Lot surveys are mere work, this is where the fun is in surveying.

This one I'll be discussing a few times.

Paul in PA

> Are the correction values universal for any EDM or must I get specific?

No - Yes you must get specific.

> How would you do it?

I would calc the refractive index of air for the conditions of observations (actual temp & pressure) that were made during field deployment, solve for the correction ppm that should have been used; then compare that to the correction ppm your instrument would have used based on your erroneous setting(s). Correct your slope distances accordingly.

You'll need your instrument's modulation wave length & modulation frequency of the EDM to calc the index of refraction for the instrument @ standard atmosphere. You'll also need the wavelength of the carrier beam (infrared, laser, etc) for which your measurements were made. The refractive index will vary based upon what your carrier beam source was.

The book usually includes the formula in it somewhere.

Doesn't the instrument just calculate a PPM?

85 degrees will result in a certain PPM which results in feet to add or subtract. This gives you the zero PPM distance. Then calculate the distance given the PPM for the real temperature.

Should be able to do this in an Excel spreadsheet.

yep, the quick & easy sol'n ;-).

For a self-enacted goof though, I like knowing more than just "what the gun tells me it is"

I'd do some tests (as you suggested) with instrument at 35° and read some long shots and then (if necessary) set another job and repeat with same points at 85°.
I'd book the lengths the instrument displays manually and compare with data later.
My jigger stores the raw data as measured and any corrections (scale factor etc) are reflected by the coordinate values of the points. (Nikon 821 with AP800 software).
I'm always wary of what the instruments actually record when settings are changed.
I suppose to be doubly sure download all data between different settings then check each job on PC.
In mine if I INVERSE between points on board, then it gives calculated distance between corrected points, not the raw data.

Unless they are very long lines would the differences amount to anything significant, taking into account plumbing errors, uneven refraction across the earths surface etc?

Temperature Correction - DONE

Set up the instrument and recorded various ppm corrections at different temperatures without changing other parameters:

temperature, correction, distance to a prism (verify correction direction)
100° +19ppm 159.776
85° +12ppm 159.775
61° +0ppm
35° -15ppm 159.770
0° -37ppm 159.767

I chose to use a correction difference of 28ppm (1/2 of the 100° 56ppm) rather than the indicated 27ppm. Rather than dividing 1.000012 by 0.999985 I just took 1.000028 and instead of inverting it just subtracted 0.000028 from 1 to get 0.999972. Having done enough combined scale factor adjustments I know the mathematical shortcuts around the number 1.

Then using point scaling in Carlson Survey I scaled all the relavent field points about one of the traverse points. Across the limits of the project to date the change reduced the most separated traverse points from 1633.857' to 1633.811'. A bit later in the project I may get to make a 1733' and 1935' traverse shots, the terrain looks favorable. To the South I have a 24.5 acre adjoiner that fronts on a road 2443' from my PQ. There are 6 called for irons along or near my PQ and 6 at the far end and very little called for in between. That is where GPS is handy, as well as to check those long traverse legs.

Paul in PA

Temperature Correction - DONE

it would have been easier to just give the pins a small kick (in the proper direction).

I'd be surprised if the difference is more than 0.01 in a thousand feet....

0.028' In 1,000 Feet

That could easily be lost in closure error, but should show up against the GPS.

Until you know the value of your error it is hard to discount it.

Paul in PA

Temperature Correction - DONE

Ahhhhhh! The elusive 0.04!

I use a Trimble TSC2. All data stored in the .job file and the .dc file are UNCORRECTED distances. Since I prefer to adjust my total station data (and RTK and static GPS) using Geolab, and also since I prefer to have more control over the process, here is what I do:

1) I read the .dc file and place all of the observations into a database
2) I can then change the prism offsets and HI/HT values if necessary
3) I can enter "more correct" values for T, P, and humidity if needed. Sometimes I obtain weather data from a nearby station from www.wunderground.com, other times I can use the ADC atmospheric sensor (which can store data through the day). The S6 has an on board pressure sensor, which I have found to be quite accurate. One warning-if using weather values for a different site, the pressure is most likely a sea level pressure, it must be reduced to station elevation
4) I then batch correct all of the distances by applying the HI/HT, T, P, H, and prism offsets. I could also apply calibration values at this step if they are needed. This gives mark-to-mark distances and mark-to-mark zenith angles.

Adjust.

So, step 3 is what you are asking about. Each type of EDM has its reference coeficient that depends on wavelength and also what the manufacturers chose to be zero. If you use survey controller, the values are stored in the DC file in the E4 record.

0.028' In 1,000 Feet

> That could easily be lost in closure error, but should show up against the GPS.
>
> Until you know the value of your error it is hard to discount it.
>
> Paul in PA

Not only "could" it easily be lost in the closure error, but it absolutely would be lost in the closure error. It is s systematic error that would compensate itself out when looping back to the point of beginning.

I agree that you may or may not care, but that you should know what you're dealing with regardless (so you know if and how important it is).