smartt1982
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Strange Weather Radar

Fri Aug 27, 2010 12:01 pm

I have seen this once or twice before and it has always been in clear weather. I have heard various reasons for it from UFOs to being scanned by a military aircraft. Any ideas?

Thanks
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tb727
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RE: Strange Weather Radar

Fri Aug 27, 2010 3:18 pm

Looks to me like the radar was pointed at the ground real quick. I do it all the time.
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BALandorLivery
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RE: Strange Weather Radar

Fri Aug 27, 2010 5:27 pm

Signal being jammed/interfeared by NATO EWACS aircraft.

Not unusual in Europe

[Edited 2010-08-27 10:29:00]
 
donniecs
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RE: Strange Weather Radar

Fri Aug 27, 2010 9:45 pm

Looks like ground return, stabilization function of the radar might need adjusting. We had the problem a few times on our Honeywell systems on the Gulfstreams. The roll was set wrong for level flight causing ground return on one side. The effect was even greater in a turn to side with ground return. It's easy to adjust but the final adjustments had to be done in flight.

Quoting BALandorLivery (Reply 2):
Signal being jammed/interfeared by NATO EWACS aircraft.

Not unusual in Europe

This doesn't sound right, I flew around a lot in Europe for a few years and never heard of this. It would be a massive safety issue if they were and would probably included NOTAMS before hand, if this was to ever happen.

The closest you'd come to this is military aircraft being intercepted by other military aircraft, usually after permission was asked, which isn't even closes to jamming radar. Now flying over Switzerland you had no choice, the Swiss like to intercept us quite a bit and we had no say in the matter.
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mrskyguy
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RE: Strange Weather Radar

Fri Aug 27, 2010 11:42 pm

Quoting BALandorLivery (Reply 2):
Not unusual in Europe

I could almost buy your first statement that it was a radar jam (though it does look like the same return I'd see when we pointed our Bendix to the ground, as tb727 pointed out) but why in blazes would the jamming of radar be considered more common in Europe?   
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BALandorLivery
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RE: Strange Weather Radar

Sat Aug 28, 2010 3:35 pm

I see it on average a couple of times a month flying around europe.

Amongst the pilot community the common perception is that the radar signal is being interfeared with by military aircraft.
 
donniecs
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RE: Strange Weather Radar

Sat Aug 28, 2010 4:40 pm

Quoting BALandorLivery (Reply 5):
I see it on average a couple of times a month flying around europe.

Amongst the pilot community the common perception is that the radar signal is being interfeared with by military aircraft.

I'm not saying your wrong but I must admit that I do have my doubts. I'm not a veteran flyer but I spent 4 years flying around Europe often times a few legs a day and never saw or heard of this. If it is radar interference then why is 95% of that radar sweep a good image, you can even make out some cells on the top edge of the DU along their track. If the AWACS was using a frequency that interfered with weather radar I'm sure that EASA would have been involved by now and this would be common knowledge and addressed since it is a massive safety issue. The above image looks like quintessential ground return from a radar that needs lateral stabilization adjustment.
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BALandorLivery
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RE: Strange Weather Radar

Sat Aug 28, 2010 5:19 pm

We need more experts here.

The thought is that the direction of the cone is the direction the 'other' aircraft is in.

I have no proof/source for info other than what is commonly thought of amonst crews.
 
eisenbach
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RE: Strange Weather Radar

Sat Aug 28, 2010 6:49 pm

As a meteorologist I just can give you an example from our "ground view". These cones appear quite often (many times a day) at our ground based weather radars - so it's nothing unusual for us. I have to ask my colleagues for the exact reason.

Here an example from the actual weather radar network in Austria:

Weather Radar Austria, UBIMET (ubimet.com)


Down in the middle of the picture you see a streak of weaker precipitation. The reason for this radial error is, that this particular radar is situated near a mountain top south of the station. So you "see" the shadow of the mountain.

At the second picture (sorry, I couldn't upload it, because of size restrictions here at this site) you finally see the same pattern as shown at the weather radar on the plane:

http://photos.eisenbach.at/upload/Radar2.PNG

These streaks are also pointing away in radial direction from the weather radars. I don't know the cause, but these errors last normally not longer than for 1 to 10 scans. I only know that the radar is sensitive to the atmospheric layering and the radar beam can bend quiet much vertically, dependent on the temperatures in different heights.

Sorry that's all I know for the moment.
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Francoflier
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RE: Strange Weather Radar

Sun Aug 29, 2010 6:45 am

I have seen those kind of returns quite a few times flying over Germany, but they also happen when flying near other major cities. They always seem to originate from the downtown area of a major city (Munich in this case).

I have always theorized that the building layout of some cities produced very good radar wave reflectors (large flat surfaces perpendicular to each other and to the ground, forming hollow pyramid shapes, like omnidirectional trihedral reflectors or 'corner reflectors'. Though why it happens in certain cities more than others, I don't know. And it wouldn't explain that exact shape of return.

Then again It might also be some kind of electromagnetic interference from a city based source. Maybe a strong transmitter that emits similar wavelenghts. Ground based doppler weather radar?

It happens when scanning over downtown FRA, amongst others.
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flybaurlax
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RE: Strange Weather Radar

Sun Aug 29, 2010 4:47 pm

Once on a flight from LAX-SEA we had a blob following us on the wx radar. We figured there was something stuck on the actual dish or within the nosecone. It wasn't the display as it would disappear when the Capt turned the radar off. We came to the conclusion that something was obstructing the radar.
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fr8mech
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RE: Strange Weather Radar

Sun Aug 29, 2010 5:38 pm

In the old days (pre-color and terrain matching) this was called spoking.

Sometimes a fault, sometimes just an anomalous event.

That's what it looks like too me.
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donniecs
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RE: Strange Weather Radar

Mon Aug 30, 2010 3:17 am

Quoting fr8mech (Reply 11):
In the old days (pre-color and terrain matching) this was called spoking.

Sometimes a fault, sometimes just an anomalous event.

I also forgot the obvious (as I did once while troubleshooting), that it can come from moisture that made its was into a delaminated area in the radome. We racked our brains for a week once trying to figure out why an aircraft was getting an almost identical image to the above, finally swapped out the radome and the problem was solved.
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YWG
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RE: Strange Weather Radar

Mon Aug 30, 2010 10:44 pm

Quoting donniecs (Reply 6):
The above image looks like quintessential ground return from a radar that needs lateral stabilization adjustment.

I agree. Looks like she's painting ground. Not sure what model this radar is but.....
If you roll while the radar has a fairly downward angle scan, it will paint the ground just as it appears to be doing in this picture. I'm not that familiar with advanced auto stabilized radars but I'm just saying it does happen on some radar i've dealt with.
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fr8mech
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RE: Strange Weather Radar

Tue Aug 31, 2010 12:57 am

Looking at it further, and not knowing the ins-and-outs of the newer Wx-RADAR systems:

I don't think it's painting terrain, because terrain isn't annunciated on the EHSI. I see that the system is in WX-T mode, which, if I recall correctly, is turbulance mode. Or am I missing something?

This code be ground clutter, but it doesn't look like any ground clutter I've seen.
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glen
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RE: Strange Weather Radar

Tue Aug 31, 2010 12:08 pm

Quoting YWG (Reply 13):
If you roll while the radar has a fairly downward angle scan, it will paint the ground just as it appears to be doing in this picture.

Definitely not. Ground clutter would not paint such a sharp cone with its tip right at the aircraft. It is circular around the aircraft like here:






When you bank the a/c, the ground clutter would just be more pronounced on the side you are rolling into.

I've seen these cones like in the thread start several times and when, they appear just a few seconds and then disappear again.
Like mentioned before, I've been told this is interference with another strong radar - but I can't say for sure, if this is the correct answer. At least it seems reasonable...

Quoting fr8mech (Reply 14):
I don't think it's painting terrain, because terrain isn't annunciated on the EHSI. I see that the system is in WX-T mode

Even in WX-T mode the radar will show ground clutter like in the picture above.
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fr8mech
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RE: Strange Weather Radar

Tue Aug 31, 2010 12:43 pm

Quoting GLEN (Reply 15):
Even in WX-T mode the radar will show ground clutter like in the picture above.

I understand that it will paint ground clutter, but will it overlay the terrain data? I'll be near an MD11 sim tomorrow and see if I can get a look.
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glen
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RE: Strange Weather Radar

Tue Aug 31, 2010 1:28 pm

Quoting fr8mech (Reply 16):
I understand that it will paint ground clutter, but will it overlay the terrain data?

Ah sorry, I did not understand you talking about terrain from the EGPWS. So you are right, it is in WX-T mode and therefore does not display terrain data. On the planes I know you can't overlay terrain data an WX-data - this would be too easy to get confused...
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fr8mech
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RE: Strange Weather Radar

Tue Aug 31, 2010 2:30 pm

Quoting GLEN (Reply 17):
Ah sorry, I did not understand you talking about terrain from the EGPWS. So you are right, it is in WX-T mode and therefore does not display terrain data. On the planes I know you can't overlay terrain data an WX-data - this would be too easy to get confused...

That's what I was thinking. So, this isn't a terrain paint. It really doesn't look like ground clutter. I can't speak to jamming, but I would expect a screen full of hash and not such a directed beam.

I'm thinking a fault. Spoking?
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AAR90
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RE: Strange Weather Radar

Tue Aug 31, 2010 2:46 pm

Quoting BALandorLivery (Reply 5):
Amongst the pilot community the common perception is that the radar signal is being interfeared with by military aircraft.

Close, but not accurate. Tactical & strategic radar use a different frequency band because the "target of interest" is other aircraft, not weather.

Quoting GLEN (Reply 15):
Like mentioned before, I've been told this is interference with another strong radar - but I can't say for sure, if this is the correct answer.

The "interference" is being caused by another airborne WX radar that is using the same (or VERY CLOSE to the same) frequency [and other characteristics]. If your radar is in "listen" mode at that particular instant in time AND is pointed in the right direction at that particular instant in time, it will see (and display) ALL the energy of the transmitting radar it receives. It gets "spooked" (or "jammed") into believing all that energy is a "return" echo.

Considering the number of WX radars in use and the limited number of "optimal" frequencies (and other design parameters) to "see" weather that are available, it is actually surprising we don't see this more often than we do. I see it at least a half-dozen times a month during the summer --thunderstorm season in USA.

Quoting BALandorLivery (Reply 7):
We need more experts here.

Does an ex-Hawkeye driver (Instructor, Natops Officer, ASO, and PacFlt Evaluator) suffice?
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glen
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RE: Strange Weather Radar

Tue Aug 31, 2010 3:24 pm

Quoting AAR90 (Reply 19):

Tks a lot for the info.
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