1. This is information on Altitude Rings is from my Weather-Radar Training.
To get started, set up your speakers or your earphones. Start the “Slideshow” either by using the icon in the bottom right corner, or the tab above, and you will hear audio on each slide--except for this one. Use your page-up and page-down keys to move through the slides. You may also use the buttons in the bottom right corner. Enjoy!
Steve Sweet
Staff Engineer
Honeywell

2. Section 12
Altitude Rings
You may have heard of, or seen, an altitude ring on a radar.
It is fairly common observation, and it does not indicate a problem with the radar system.
Let’s take a look at one and see how it happens.
12/09/02
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3. Altitude Rings
Here is a typical “altitude ring” in a jet at 41,820 feet with the antenna pointed up +15 degrees. The aircraft is a Falcon 900EX jet operating a Primus 880 radar with an 18-inch antenna.
Notice the “altitude ring” is located at about 7 NM. The aircraft is 6.9 NM above the ground.
12/09/02
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4. The next slide demonstrates that situation:
Altitude Rings
Snell’s Law:
If electromagnetic radiation is directed toward a flat-reflective surface, the incident angle of the energy will be equal to the reflected angle of the energy.
Incident angle
Reflected angle
Reflective surface
The next slide demonstrates that situation:
12/09/02
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5. Altitude Rings
Altitude
in Feet
40,000
30,000
20,000
10,000 10 20 30 40
Range in NM
Snell’s Law a
+15 degrees tilt a
When the antenna is pointed up at a high angle, like +15 degrees, a small amount of the energy (approximately 5%) reflects off the inside of the radome (Snell’s law) and is re-directed almost straight down.
This reflection gets even stronger in rainy conditions because more energy reflects off the inside of the radome, and the ground is wet making it more reflective than usual.
The energy will travel almost straight down to the earth and back. This is not a radar problem. It’s just an annoyance.
12/09/02
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