Brian McEachern, post: 384219, member: 9299 wrote: Three miles! And I see Kent says six miles! At 3500' I have a hard time seeing anything except the 6' or 7' streamer of ribbon blowing off of the pole.
The trick, such as it was, to finding a prism in daylight at six miles was to use a mirror to light it up with a flash of sunlight. You just sweep the general area and the prisms light up and you are ready to point the EDM at it or to measure angles to it. In dim light, a bright flashlight works just as well.
Using a visible laser EDM (as I was), when the EDM hit the prisms, there was a splatter of a bright, glittering ball of laser light that confirmed you had the EDM pointed at the prism.
For measuring zenith angles and horizontal angles, the illuminated prisms made a pretty good target in most conditions aside from severe daytime refraction.
Any dilution of accuracy in shooting such far distances?
Bill93, post: 384199, member: 87 wrote: If I remember correctly the maximum distance increases by a factor of sqrt(sqrt(prisms)) when the limitation is beam dispersion. That may not apply when atmospheric absorption is the limiting factor.
The bottom line is that it is hard to get really long distances.
The moon landings put up an array of about 100 similar prisms and it takes a powerful laser and powerful telescope to get a return.
Cool that you mention that, Bill. I have a friend that works for NASA at Goddard SFC here in maryland. he operates satellite laser ranging; measureing to the lunar prism array, the ajisai satellites, and others. his laser lights up the night sky, especially when he measures ajisai
From the NOAA photo library
With 9 prisms and a strobe light for a target I have taken 5 mile shots at night.
I still have a 3 prism & 9 prism setup in the garage somewhere. Cannibalized the glass off most of them over the years, We used them years ago on runway projects at JFK, which are over 3 miles long. Also on long shots at landfills on Staten Island.
Do a little trig to figure out the potential error built in on such long shots due to the gun not necessarily being aimed dead center. Then compare that to the potential error in running a six leg traverse to achieve the same thing.
Brian McEachern, post: 384250, member: 9299 wrote: Any dilution of accuracy in shooting such far distances?
No. Ranges of six miles were within the EDM specification. Best results required measuring barometric pressure and temperature and that those values correctly represent the average of the line. In the work I did, the terrain was rolling, not mountainous, and the changes in ground cover and elevation were relatively minor, so the measurements at the EDM worked perfectly well for the line. The net scale error in the conventional traverse when checked by GPS years later was under 2ppm over about 16 miles.
Sidetrack
A few years back, I was driving through town in a residential neighborhood when I saw a crew doing topo along a quiet street. They had a TS with handheld radios and were picking up inverts of culverts, water and gas meters, PPs, sidewalks and fences etc. City job for drainage study and improvements. What caught my eye was the goofy looking rodman who was taking shots using a triple prism at close range. I knew the company owner vaguely and thought about calling him but what could I say.
The very fact that this thread exists, is a sign of progress. We are fast moving into a world where GPS has taken the place of Long Shots.
As a side note, I have exceeded the limits of my triple Prism, and had to set a "Chaining Nail" in the middle, and shot the dist from BOTH ends.
And, I have had to go and get my Autoranger S EDM, to shoot long shots. Because, the total station did not have enough EDM in it.
I don't miss having to shoot long shots.
Nate
Kent McMillan, post: 384171, member: 3 wrote: I had a nine-prism cluster that worked well for measuring EDM ranges of six miles or so in daytime conditions. It was a lot of glass, but was what was needed to get enough of a return signal to measure a range. Considering how well GPS vectors agreed later with those EDM range measurements, it did the trick.
When I was surveying at DMA (now NGA) we had 9 banks and 18s- Didn't need them often but when we fired up a monster like the Ranger VA or a Rangemaster and shot a 9 bank you could easily go 30K. We did some long stuff and the results were always very good. Of course we turned all of our angles with T3s and lots of Astro work. The sweet old days.
Me to the Party Chief -> "Do you think we be able to get a distance with a single prism?"
Party Chief to me -> "Better take the triple just in case."
Me to Me -> "Dam! One more thing to pack."
I can remember placing the single on top of the triple just in case. Those were the days where we were using hand signals. You didn't want to hike back down the hill only to find out the PC didn't get the shot. Happened more than once.
Thanks for the info.
There are not many places here that a long site can be made without there being a cross country power or pipeline or highway.
the three triple prism I have will connect together to make a 9 prism setup in either a triples on top of another or a large triangular array.
Some days making a couple of setups and long shots are easier than spreading out two control points for the static GPS.
There are some areas that it is tough to find a suitable control point location and we really have a lot of trees and some really deep holes blocking the horizon to have enough satellites in view.
The colors red and white have always been the best colors for me to see for a sight and using a light behind or in front of the prism to lock onto has made it work.
It takes a bit of coordinating a plan to pull everything off most of the time and people at each end that understand what to do and when to do.
I once worked with a crew member that had a florescent orange coveralls and we used them to find objects at long distances.
Sighting the reflected IR or Lazer light from the prism works best when it is so far away.
Most of these new pocket radios will not reach 17k feet, the CB radios we used in the late 70s were much better except they were the size of a stick of bologna and had a retractable antenna about 4ft long.
A Harris, post: 384401, member: 81 wrote: Most of these new pocket radios will not reach 17k feet, the CB radios we used in the late 70s were much better except they were the size of a stick of bologna and had a retractable antenna about 4ft long.
Yep, the old handie talkie radios, took about a dozen AA batteries, and the squelch was always on. These silly toys they have today that barely reach across the truck with their advertised range of up to 7 miles get left behind a bunch.
We used to do it all the time, they just sit in the shed now, had a HP distance meter, thing was heavy to carry up the hills, but it would easily locate a prism cluster at 30,000'. You could pick out the Ice Cream bucket on the 5' section of tubing it all sat on easily at 5-6miles
I was once told by a party chief that thought he was the "gift" to the survey world that EDM stood for Energy Distance Measurement. I think he needed about 9 prisms to measure his energy.
Brian McEachern, post: 384492, member: 9299 wrote: I was once told by a party chief that thought he was the "gift" to the survey world that EDM stood for Energy Distance Measurement. I think he needed about 9 prisms to measure his energy.
About 35 years ago, I heard a licensed surveyor describe an EDM as an "Electronic Distance Machine", which I suppose was technically correct, but amusing. It's too bad he isn't around any more because I would have been interested to have him tell me that GPS stands for "Geo-Position Surveying".
