Radar Beam Height Calculator

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Radar Beam Height Calculator

#1 Postby wxman57 » Wed Jul 26, 2006 1:58 pm

I keep reminding everyone that when you're looking at a radar image to try to estimate whether or not there's a surface circulation forming, that you're often not looking anywhere near the surface. Because the radar unit is typically anled upward at about 0.5 degrees, and the Earth's surface is curved, the radar beam is higher and higher above the ground (or water) the farther the echo is from the radar unit.

Searching the net, I found a neat calculator that will give you the height of the radar beam above the surface if you can estimate the distance from the radar unit to the echo that you might be identifying as a "swirl".

http://www.wdtb.noaa.gov/tools/misc/bea ... width.html

Some general values:
25 miles = 1800 ft up
50 miles = 4500 ft up
75 miles = 8100 ft up
100 mlies = 12,600 ft up
125 miles = 18,000 ft up
150 miles = 24,300 ft up
175 miles = 31,500 ft up
200 miles = 39,700 ft up

As you can see, using long-range radar to identify an LLC is a bit pointless. At 150 miles out, the radar is looking over 24,000 feet above the surface of the water. There's no guarantee that the spin you see 6 miles above the surface extends down to the surface.

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#2 Postby Aquawind » Wed Jul 26, 2006 2:34 pm

That is excellent.. Thank You! That should help people understand the concept some many have had to repeat for years..

some many? LOL geesh.. edit that to .. so many.. :roll:

It's amazing I can breath and walk at the same time..
Last edited by Aquawind on Wed Jul 26, 2006 2:48 pm, edited 1 time in total.

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Re: Radar Beam Height Calculator

#3 Postby Air Force Met » Wed Jul 26, 2006 2:38 pm

wxman57 wrote:Searching the net, I found a neat calculator that will give you the height of the radar beam above the surface if you can estimate the distance from the radar unit to the echo that you might be identifying as a "swirl".

Do you remember the "smile-e-gram" that was used with the old FPS-77?

Wow how we have progressed.

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#4 Postby x-y-no » Wed Jul 26, 2006 2:41 pm

This is handy, thanks.

I've done rough calculations by hand once in a while, but I keep forgetting the results and I'm too lazy to do it again. :lol:

For those using this, if I recall correctly, Base Reflectivity 1 is 0.5 degrees, BR2 is 1.5 degrees and so on.

Someone please correct me if I'm wrong.


#5 Postby Rainband » Wed Jul 26, 2006 2:48 pm

Thanks 57 that is cool :D

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#6 Postby M_0331 » Wed Jul 26, 2006 4:10 pm

Very good info which we can use on a daily basis as we view our radar.


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#7 Postby mtm4319 » Thu Jul 27, 2006 1:25 am

From how far up can you generally see an LLC on the radar? 24,000 feet would surely be too high, but is it discernible from, say, 10,000 feet?

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