How harmful is Wx radar?
 

In our company SOP it says that, during taxi out, the Wx radar can be switched on when needed.

In reality this becomes a standard item during taxi, whereby almost everybody switches the radar on regardless of people, airplanes, vehicules, fuel tanks in front of them.

My question to you:

1) Wx radar is harmfull for human beings. What is the danger zone? 1m/5m/50m?

2) How bad is it to switch on the Wx radar when you have a large metal object (ie plane or fuel tank) in front of you? Can this damage the Wx radar itself?

3) What do most other companies do? Switch Wx radar on during taxi or when lining up?

4) Do the military still use civil wx radar beams to identify civilian traffic in sensititive zones (gulf region, Iran,...)


Thanks

View from the Health Physics Society on wx radar
 

Health effects of exposure to radar microwaves

Not associated with them, just posting the link.

1) Depends on how powerful the Antenna is. Most Antennae usually have a minimum safe distance where you will be OK from exposure. Most modern Wx Radars are very low-powered and have very close safe distances. I believe the safety issues are dealt with in the manuals???

2) No, because the metal reflects the transmission which will be received by the Radar as normal. If it's a high powered Antenna and you are close behind though you may get a little warm :) as may the occupants of the aircraft in front... as for the fuel tank however... :uhoh:

3) Not sure, I'm only an engineer, but I have heard that many switch on Tx when lining up for departure, others during taxi (there is another thread on this subject just now).

4) Don't know.

Most modern WX radars talk about 5m safety distance.

It might not be very dangerous but the energy emitted by the system is still far higher than any other source like communications (handphone, satellite, WLAN etc). So as long as we are not sure if these sources are dangerous, I would be somewhat cautious and don't use it beyond the manufactor limitation.

It is widely accepted that one only uses it in the air or lined up on a runway, sometimes already on taxiways when pointing away from ground handling personel.

Biggest misconception about radar emissions is that their radio waves are different to those "unhealthy" ones, like the radio activity (alpha, gamma particles). The later can be summed in your body and finally lead to cell destruction. Radio waves from radio emitters are different: They only are harmful if you get too much per time unit. They don't sum up in your body. You can compare it with your microwave oven: If you sit in front of it, your dosis is minimal, if you're inside, your body gets boiled.

Dani

I was just wondering ... is it safe to spot airplanes near the runway (landing and taking off) ??
(Is there any additional risk of contracting those harmful emissions if an aircraft on finals, flies directly overhead, say, at ~1000 - 1500 ft ?)

shanx
 

No.I dont believe you are in danger.(unless you are quite close) Modern wxr is relatively low power approx 100 watts I recall BUT the antennae are very directional which in short means that 100 watts ( for example) is effectively multiplied many times as its basically all in the one direction.
Output power is usually measured with an imaginary perfectly omni directional antenna called an isotropic radiator.

When that 100 w is fed into a modern plate (or any other directinal antenna) we use ERP or effective radiated power.
So you have a concentrated beam but it is very directional so if you are spotting you are still some distance away and as the plate scans you are not in the beam for extended periods.
With the inverse square law the power diminishes fairly quickly too.

I would say you are more at risk with the more powerful land based radars in operation around the fields.

I would think that minimising exposure to any high energy RF field is a good idea.More so the high end frequencies such as DME/ATC/TCAS then up to Rad Alt and then WXR which is a much shorter wavelength still.
They are not anywhere near the very short hi energy x ray band that can act at a cellular level. The jury is still out on what and how much damage is done but surely the less the better.

In answer to the one of the original questions it depends on the wxr used.ifyou are flying an old 727 or f28 for example you could be transmitting many thousands of watts thru someone. Not good.
"safe" distances on modern a/c are a matter of meters only but why take the risk.use it when you are clear of people and lining up would be sensible.You wont get a clear shot of anything until you clear the terminal and other reflective material anyway.
In the end vendor/company policy dictates but minimising exposure I think is wise.

It's not recommended, even though all modern radar receiver circuits have tunnel(?) diodes (or something similar) which prevent damage to the circuits when strong signals are received (from reflections and nearby radars).

Agreed.NSEU. It would be hard to envisage any tx/rx without rx front end protection. Reco not too regardless.

as for firing any radar at a fuel tank /tanker. If you do wear sunnies and ear muffs.Unlikely to blow but I would not be tempting fate too much.
Use of any hi power rf source is not a particularly good idea around fuel/ being fuelled etc.

I thought it was a given that you never transmit an RF signal in an explosive atmosphere (fuel vapours etc.), lest things go kaboomski :uhoh:

Captain S

yes capt I did understate that fact with a little humour.:eek:

difrips, this is what the Australian regulations say, I'd bet there are similar rules in your own country.

If you consider that the spacing between runway edge lights is normally 60 metres you'll realise that 37 metres isn't very far but it's probably unwise to just turn the thing on without thinking about what's around you. Our company procedure is to turn it on, if required, when entering the runway with the intention of taking off (ie. not when just crossing a runway.)

God I hope they are not harmful, not after over 40 years flying around in a radar filled environment.

Nr. 4 above.

Yes, there is an International NOTAM out advising civil operators in the Gulf and surrounding areas to operate weather radars continuously. Don't know about Afghan overflights, but probably not a bad idea.

GF

6.1 -- 25,000 Watts
 

Arinc 700 radars, which began production in 1981, are less than 150 watts peak power, which is less than 1 watt rms, heating power. Your kitchen nuke is on the order of 750 watts rms.

If your old airliner's WX radar has a standby mode, then it is usually a high powered, pre-Arinc 700 radar. Only TWA kept the Standby mode when they transitioned to Arinc 700 radars, to minimize pilot training.

Have you ever thought about DME?

GB

Ah good point, hadn't considered that the weather radar is below 25kw.

Radar ground threat
 

Most modern radar equipped do not transmit the amount of power as the older non-flat (convex) antennae did in the past.

I think I posted before most modern wxr's are 100 watts up the stick or so whereas the older gen stuff could be tens of thousands of watts and definitely will do some damage with extended/nearby exposure.

Also do not discount the ERP with 100 watts concentrated into a 3 degree lobe which will give you an effective radiation of thousands of watts, so be careful no matter what.

Last time I looked wxr was in the in the order of around 13 gigahertz.
Well above microwave ovens therefore much smaller wavelength at around 2 to 2.5 cm I think. Still much bigger than cellular level but still worth caution.

Someone mentioned DME .
Indeed, lower freq around a gigahertz but quite a hi peak power ~ 500watts.
Rad alt is around 4.3 gig If I remember correctly.Lower power but still up there in freq and I think worth avoiding where possible.

On the tarmac we are constantly being bombarded with all manner of RF signals.Some at close range.
I'm not convinced we are killing ourselves any quicker with RF and i think we have other more immediate OH&S issues like air quality and chemical exposure.I'm in the "less is likely better" camp.

Also I think some folks do confuse radio freq radiation with nuclear radiation. 2 different things altogether.

I doubt very much that any modern equipment uses tunnel diodes. Unlike other semiconductors, they have a limited life because of the very high doping density leading to further diffusion at room temperature.

The effects of RF are, as far is known and can be reproduced, limited to thermal effects. This means that the radar duty cycle (pulse length and time between pulses) comes into play, as does the length of time the exposure happens. For fuel ignition, there is a DEF STAN on the subject.

100 watts into a 20dB gain antenna gives 10kW ERP: however, there is only 100 watts available to heat somebody up.

at worst it is just a cheap method of birth control
 

... after that its the eye humours which are most vulnerable I think so no worries !

radeng: That 100 watts is pulsed power, maximum of 1500 pulses per second, of about one microsecond width. 1,500/1,000,000 = 0.15% duty cycle = 0.15 watts average power. You probably generate that much electricity with your saliva.

Fearing modern radars is spitting in the wind.

GB