The recent thread discussing efforts to establish an ersatz calibration baseline due to the absence or decrepitude of existing NGS calibration baselines raises the question of why this situation exists.
While I have been retired for a few years now, I believe the statements below to still be accurate. Corrections welcome.
There was an NGS staffed program to establish EDM calibration baselines around the US. It supported the need of users to verify the performance of their equipment by providing a link to the national standard of length via equipment whose performance was calibrated and verified by ties to the national standard maintained by the National Institute of Standards and Technology. (NIST).
This NGS manned program was discontinued in favor of a cooperative one where a state or local group worked with NGS to establish or remeasure a CBL. NGS provides to trained personnel (including state advisors), the specialized equipment including two calibrated EDM units, collimators, weather instruments, CBL disks, and more for these purposes. They also provide detailed instructions, data collectors and software on the data collectors to guide users through the process.
NGS has neither the resources nor staff to take on this activity without help. Without continued interest in this activity I doubt that the funds used to update and maintain the equipment will continue to be allocated.
The entity desiring a CBL or wishing to remeasure one must provide an appropriate site. They must set the monuments and they must assist in the measurement under the supervision of someone who has taken the NGS CBL training.
After the measurements are made (and valid checks obtained), NGS will adjust the data and post the results on their web site.
This is a deal for surveyors and others wanting a CBL. Unfortunately, more people talk about wanting one than commit to getting one. It is a long term commitment as a freeze-thaw cycle must take place after the monuments are established.
Contact the NGS advisor for you state for more current details.
Mike:
As I remember it you are correct about the training of locals to maintain the baselines. There are a few problems though. First the people that were trained are getting old and have never used their training, that I know about, in MA. The locations of several of the existing baselines has been compromised by development, that is what we get for placing them at airports. It is rather hard to find level open terrain here in MA (except "the Cape") so moving the baselines would be quite involved and expensive. For now everyone has to find a baseline that is still assessable and in working condition, I don't know what will happen in the future.
T.W.
Good point.
We had one in town, it was around a lake.
Well, eventually someone discovered that shooting an EDM over water was not "stable" enough for establishing a baseline. So all that work was basically for naught.
"Provide An Appropriate Site" There's The Rub
The best locations for long clear sites are off limits, along highways and airport runways.
One I know of along a highway was far off the pavement for safetly. Well they stopped mowing that far about 15 years ago. I did not even get out of the vehicle to look, much less start clearing.
Another was placed on a military base along the runway. The base was closed and the township aquired it for a park. However they sold part of the park for a gated development. The first point is less than ten feet in both directions inside a 6' high iron fence which you would have to shoot through. There are untold ways that it could have been kept accessible, but nobody cared.
Paul in PA
In 2005, the Arkansas NGS Advisor helped establish several calibration base lines. They are avaliaable at the following web site: http://www.ngs.noaa.gov/CBLINES/BASELINES/ar
Notice in particular the location of the baseline at Little Rock. The residents there even volunteered to dig the holes for the monuments.
> Contact the NGS advisor for you state for more current details.
A few years back I sent my crew out to baseline our instruments on the baseline near Hillsboro, OR. They found that the DOT had installed a large green highway smack in the middle of it. Now, the DOT had a written policy that their crews were supposed to baseline their instruments before beginning a project or not less than every 3 months. And they had several crews working in the area. But the sign had been there at least 6 months at the time. Not to mention the local county surveyor had crews, and the dozens, maybe hundreds, of private surveyors in the area.
I might note that in the Pacific NW a relatively small proportion of work is done with GPS RTK, due to the tree cover.
I recently sent my crew out the the baseline near Tulsa. They report that the monuments are all in, but that the vegetation has overgrown a portion of the line. This is the only existing baseline in the state of Oklahoma. I know that because the state DOT Survey Manager contributed a story to the "Sooner Surveyor" earlier this year stating so. OK DOT has dozens of crews, all with total stations in their kits. Nobody could have used this baseline in years.
These things aren't being maintained because (nearly) nobody is using them. Not even the people who say they are.
Period. End of story.
BTW, Oklahoma doesn't have a state NGS Advisor.
"Provide An Appropriate Site" There's The Rub
Not a real big problem out west. Doesn't seem to make a difference.
You raise a good point, there, Norman. The question I would raise, however, is whether ANYONE who has checked their EDM against a calibration base line EVER found it to be "out of calibration?"
I know the early instruments that required you to dial in the frequencies had issues, but has anyone ever had issues with the "modern" EDM's?
Are the requirements for calibration checks just a throwback from the days of compass and chain? Or, are they really necessary/helpful?
Just curious.
JBS
Mark,
ODOT moved the sign and now there is a clear shot again. On top of that, there was a big utility job that ran along Hwy 26 a couple of years ago and someone actually had the foresight to protect the stations prior to construction.
John
JB - I think you've got it
Modern EDM's measure correctly if they are measuring at all. What you are really checking is your system and settings that you may need to input. That's why the procedure I outlined below for using your own EDM to establish your own CBL is valid.
And besides, the average surveyor really isn't measuring to the accuracy that he thinks (wishes) he is most of the time. I strongly suspect that even I could go observe a field crew and 90% of the time find something wrong with their procedures.
> You raise a good point, there, Norman. The question I would raise, however, is whether ANYONE who has checked their EDM against a calibration base line EVER found it to be "out of calibration?"
Yes, I have. Not by a ton, but by several times the gun's rated spec.
For a long time I subscribed to the notion that since I incorporated both GPS vectors and total station measurements into my adjustments I didn't really have to worry about baselining so much. If an instrument was "off" it would show up in the residuals. Still, we baselined our stuff once a year. Ongoing contracts with the DOT required that we produce baseline reports not more than a year old.
But we had an issue where one of our 3 instruments was measuring about 0.04' short. Just enough to be a nuisance. Back sight checks wouldn't quite work, but not by enough to stop work. Control adjustments were a bit sloppier than I liked, but not bad enough to fail. The problem, and the problem gun, wasn't identified for several months. The fix was a new "board" in the problem gun.
Right after that was when I set up our ersatz baseline near our office.
I participated in this process several years ago. The NGS provided the equipment and an advisor. They were very strict in the fact that all they could do is advise. The local agency had to physically do the work and take the readings.
It was an interesting project.
The baseline is located along an abandoned taxiway.
I have never seen any local surveyors using the baseline when I am there.
> The question I would raise, however, is whether ANYONE who has checked their EDM against a calibration base line EVER found it to be "out of calibration?"
>
> I know the early instruments that required you to dial in the frequencies had issues, but has anyone ever had issues with the "modern" EDM's?
>
> Are the requirements for calibration checks just a throwback from the days of compass and chain? Or, are they really necessary/helpful?
I would say that there has to be some kind of reference to a reasonable standard.... legally, this provides a method to prove the instruments are functioning properly. Otherwise, land disputes could quickly degenerate into debates about "whose instrument is more accurate". Even a highway patrol officer has to attest to the calibration of their radar gun when testifying. The NGS calibration baselines provide an easy and industry-wide acceptable method of verifying EDM readings.
However, I must say that over the course of over twelve years in NJ, where annual calibration is MANDATORY, I have not yet found an instrument far enough out of calibration that it needed to go into the repair shop for that reason. (This includes our roster of over 14 crews per year, sometimes more.) The vast majority of EDM problems do not involve incremental errors of a few hundredths.
In addition, along with out regular servicing and cleaning, the repair shop will supply a "certification" that the instrument is functioning to the manufacturer's standards. However, this "certification" is not traceable to NIST standards.
> ODOT moved the sign and now there is a clear shot again.
Right after my crew reported I got Roger Galles on the blower. He was interested, and underutilized. The sign was moved about 6 months later. I've been there myself since.
I'm glad they protected it from recent construction. I'm looking forward to using it again. It's more convenient than the Aurora line.
But I'll bet you money that nationally not 1 surveyor in 50 has baselined in the last 5 years. Maybe 1 in 20 in the NW. But not 1 in 1000 in Oklahoma.
Steve,
And when you go to the Little Rock Baseline you have to learn a new term:
"Shakin' the bush, Boss"
DON'T FORGET TO CALL BEFORE YOU GO!
:beer: DDSM
