For Xmas I purchased a Leica TCRA 1101+. Old instrument no doubt. Mine was built in 2001. But she's exceptionally clean and came with the RCS1100 controller, the radios, and a 360 degree prism. It was a great deal.
So, having this new instrument laying around got me itchy to hit the CBL.
Our first stop was the Valhalla, New York baseline.
We recovered the 0 meter mark. The line runs through the "gap" in the trees.
Then we found the 710m mark on the jogging track.
Of course we approached from another direction and nobody saw that sign until later.
And so the Police appeared in minutes.
That's him between the field trucks.
We explained things and away he went.
Unfortunately we couldn't find the 1190m mark.
Looks like it's been destroyed by a dirt road extension.
So we headed to the Morris County, New Jersey base line.
We've had a bit of "trouble" with distances measured to the 150m mark for years.
But we measured to and from it anyway. Good practice for the boys. We have trouble with these hedges so we "trim" them every year. If I could only figure where to send the landscaping bill...
Setting up with the Leica Zl Optical Plummet at the 0m mark.
The observations at Morris were decent, with the exception of the 150m mark.
So I grabbed two of the field crews and my instrument and we went off to the Skillman, NJ base line. With three vehicles, four tripods, four precision GPH1P prisms, and three instruments we calibrated three instruments in a little over four hours. Unfortunately we also had four hours of downtime waiting for a sleet and snow storm to pass. In fact it was so foggy and humid we often had difficulty just seeing the 1 kilometer monument.
We set up a spreadsheet to reduce the local pressure to sea level, record the observations and reduce the slope distances with a geometric conversion. We set the proper atmospheric corrections in the instruments and ignored the 'second velocity correction' as it is miniscule even at distances of over 1 kilometer.
It also calculates our 3 sigma rejection limits so we can determine the validity of each observation in the field.
The Xl sheet calculates the scale and constant and the standard errors of each.
A nice pic of the ground conditions before the snow and ice storm hit.
Now, a nice piece of freeware is calibrate by PrimaCode Technologies.
Its very easy to use, reduces the need for the 'geometric reduction' and prints a nice report.
The input is very easy and self explanatory.
As I said, a nice report follows.
And, it looks like that used, but new to me, TCRA 1101+ (which is specified as a 2mm +/- 2ppm instrument) is doing very well at 0.5mm and +1.2 ppm even on a poor weather day.
Great post! Thank you.
Cheers,
Mooshe & Henry
Scott: glad to hear that SOMEBODY still calibrates regularly, besides me.
Our last calibration was at a new CBL in Ohio (CULVER DAVIES) that uses pillars rather than ground monuments. I didn't go myself last year, but probably will go sometime this spring (on a nice warm day!).
Nice post, thanks for putting all that info out there. I just use the NGS program calibrat, I will have to give that other software a try. I use a database and a custom program to apply corrections (applied in the office) for temperature, pressure, humidity, and reduce to mark-to-mark distances.
AH...the old Skillman Baseline! I've checked many a total station there myself...
Thanks for posting about the freeware. I may have to check that out.
Kind of hard to see you on the ground! Where are the dizzying photos from 1000'? 🙂
Dennis Drumm at Primacode has developed a few nice programs, in addition to being chair of our Board of Registration!
Great post, Scott.
It's been a while since I read the spec's for building a CBL, but it seems like the ground elevation couldn't vary much more than 20' between monuments. In the picture looking through the gap in the trees, it looks like that bottom is lower than 20' from the line of sight. Is it an optical illusion? Maybe I'm remembering wrong? Great post though.
The Valhalla line sloped considerably.
0m = 147m.
710m = 132m.
860m = 131m.
1190m = 129m.
Maybe 30m to 50m in front of the 0m mark there is an intervening "finger" or small ridge on line to the 710m mark.
My CBL at Campbell Airstrip usually gets covered with snow when they plow the runway. What with the +48 or so we've had with the rain and all, maybe I will take a trip out there before it snows again. Sorry for you're weather down there, we'll have to enjoy the balmy weather here while it lasts.
-JD-
"Calibrate" is a very nice piece of software. "Transform" is priceless...
What is that orange thing on the tripod?
That is a ZNL, a zenith nadir plummet. A much more accurate way to center a tribrach over a point than using a standard optical plummet. I have an older model, Wild green.
