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sho69607
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Terrain Radar vs. Weather radar- do both pose a risk of radiation?

Sat Jun 26, 2021 9:01 pm

It is my understanding that weather radars pose a significant risk of radiation and are turned off when the aircraft is on the ground near the ramp/terminal area, but does a terrain radar pose the same risk? I am not a pilot, but I am just curious how these two systems work.
 
GalaxyFlyer
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Re: Terrain Radar vs. Weather radar- do both pose a risk of radiation?

Sat Jun 26, 2021 9:05 pm

Radar is radar, so yes, either at close range, say under 100’ from antenna are a radiation hazard. One short exposure isn’t gonna cause cancer, new radars have quite low power outputs.
 
kalvado
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Re: Terrain Radar vs. Weather radar- do both pose a risk of radiation?

Sat Jun 26, 2021 10:06 pm

GalaxyFlyer wrote:
Radar is radar, so yes, either at close range, say under 100’ from antenna are a radiation hazard. One short exposure isn’t gonna cause cancer, new radars have quite low power outputs.

It is not about cancer.
Weather radar, as far as I understand, works in X-band (8-12 GHz), where water absorbs heavily. Once a wet object (such as a bird) enters the beam, it starts heating from inside. Think about putting that bird into a microwave. Well, not really - water absorption peaks around 20 GHz, and househole microwaves operate at 2.45 GHz to allow penetration deeper into food chunks, around 3". X-band radar will provide more crusty cooking
This exposure is not cummulative, it is just an interior burn. Burns, in general, are hard to treat, burns of internal organs are exponentially worse.

Terrain radars, as far I can tell, can operate in:
X-band (see above);
L-band (1-2 GHz, cooking in deeper into the meat chunk.) If I remember correctly, some commercial microwaves for larger chunks use 1 GHz to achieve more uniform heat-through.
P-band (0.25-0.5 GHz) which may be something a bird may be able to get away with for some time. Not totally safe, but definitely safer.
 
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Starlionblue
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Re: Terrain Radar vs. Weather radar- do both pose a risk of radiation?

Sun Jun 27, 2021 12:32 am

sho69607 wrote:
It is my understanding that weather radars pose a significant risk of radiation and are turned off when the aircraft is on the ground near the ramp/terminal area, but does a terrain radar pose the same risk? I am not a pilot, but I am just curious how these two systems work.


Airliners have no separate terrain radar. It's same system, but with a different setting.
Last edited by Starlionblue on Sun Jun 27, 2021 12:33 am, edited 1 time in total.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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zeke
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Re: Terrain Radar vs. Weather radar- do both pose a risk of radiation?

Sun Jun 27, 2021 12:33 am

sho69607 wrote:
It is my understanding that weather radars pose a significant risk of radiation and are turned off when the aircraft is on the ground near the ramp/terminal area, but does a terrain radar pose the same risk? I am not a pilot, but I am just curious how these two systems work.


This is incorrect, the harmful radiation is ionizing radiation of extremely high frequency (x rays, cosmic rays, gamma rays, hard ultraviolet), and not non-ionizing radiation at the far lower frequencies used for radar systems (weather radar or radar altimeter) and microwave ovens.

There is no terrain radar on an airliner, it is a weather radar, it has a terrain function which is about how the computer displays the returns.

This is from the Honeywell RDR4000 pilots guide.

MAXIMUM PERMISSIBLE EXPOSURE LEVEL (MPEL)FAA advisory circular AC 20-68B defines the method for determining the MPEL boundary. All personnel should remain beyond the distance indicated in the illustration below. Manufacturers are required to calculate two distances; the MPEL boundary is determined by the greater of these two distances. The first distance is the near field/far field boundary which is the distance from the antenna that it takes forthe beam to form. For the RDR-4000 this distance is 14 ft(4.27 meters). The second is the distance where the radiation level exceeds the U.S. Government standard of 10 milliwatts per square centimeter. For the RDR-4000 this distance is 11.8 ft (3.58 meters)from the antenna. In TEST mode the system transmits two 550microsecond pulses at the beginning of the test sequence and the safe distance is 0.8 inches (2.1 centimeters) from the antenna during this period. The safe fuel distance is 3.5 ft (1.07 meters) from the antenna.
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
Woodreau
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Re: Terrain Radar vs. Weather radar- do both pose a risk of radiation?

Sun Jun 27, 2021 5:41 pm

The weather radar can be used in mapping mode.

But the terrain display for GPWS does not use the radar. It is a virtual terrain database. All of the terrain and obstacles are in a database and the aircraft’s position is compared with the terrain database to provide the Enhanced portion of the GPWS. The basic GPWS runs solely off the radio altimeter.
Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
 
mxaxai
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Re: Terrain Radar vs. Weather radar- do both pose a risk of radiation?

Sun Jun 27, 2021 10:50 pm

Radars (and some other electronics like CRT monitors) can emit undesired X-rays, which are ionizing unlike the regular radar emissions.

It's more an issue with (very) old radars, though, or rarely in the case of malfunctions. The regulation to turn off the radar on the ground is primarily to avoid having an open-air microwave as described by kalvado.

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