# Finding heights

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Queston for the surveyors on here...

Is there a relatively simple way for one person to measure the height of a radio mast? I am trying to confirm a mark (BM0975) that doesn't match the description given on the NGS datasheet. The official sheet shows a "recovered in good condition" by USPSQD on 2003-07-20 (also in 1994 and 1999).

Delorme Street Atlas now shows that location to be KMBV-FM radio (which is possible, I guess). I've talked to the engineer that maintains the tower now, and he believes it to only be ~230 feet, while the original was 310. So, there's the background on my question.

Trigonometry

Make a right triangle, measure from the base of the tower a distance that will you easily let u measure the angle from the base to the top, preferable longer than the height. Use you home made clinometer to measure the angle. You will have 2 angles (1 90° as base of tower to u) and included side. If the ground is not level it will require more thinking.

Tan of Angle measured x distance from tower = height of tower

You need a Clinometer to do this easily. Here is a good one at Forestry Suppliers

Or you can use a simple compass that has a hole in it and a paper clip. You need to measure the angle from the ground to the top of the tower

If you don't have calculator to solve, post the info here and I will use my trusty HP48GX and TDS COGO to solve if. The better the meaurements the more the accuracy.

You could always stake out the tower and try to meaure the length of the shawdow it casts, don't know how accurate that will be.

[This message was edited by elcamino on September 26, 2003 at 02:55 PM.]

Thanks, elcamino! I never thought that trig would come into play...thought I was done with that my sophomore year in college!

A quick and cheap clinometer would be a short piece of PVC pipe (1/2" to 3/4" diameter), a cheap plastic protractor, length of string, and a weight.

Now the easy way that doesn't require any math crunching would be to move till you see the top of the tower through the scope (pipe) at an exact 45 degrees angle. Then take the height you were holding the clinometer at (your eye level) and move that distance further from the tower. That point is now exactly the same distance from the tower as the tower's height.

--- J

RACooper -

I discussed that a few months ago here.

Since posting that, I took a bunch of measurements at a local radio tower using a Suunto Clinometer but the results weren't accurate closer than about 20 feet in height.

I used a Suunto Clinometer like this one. Along with a degree scale, it has a percent scale that makes the calculation of height easy.

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