Wx radar clutter "mistery"
 

Does anyone perceived that the wx radar "usually" clutters (saturates) more oftently during the approach inbound phase, rather than the climb out stage?
Any theory? :)

Yes. When at low altitude and/or with the antenna pointed downward, ground clutter is highly probable. If no automatic tilt control mode is active or is not performing satisfactorily, then using the manual tilt control to point the antenna upward will eliminate ground clutter and provide more useful returns! :)

Sorry but I did not express myself correctly.My point is that I noticed that wx radar saturates (no attenuation) more easily on approach than on climb , even if you work with the tilt,gain,rane, etc.
e.g: On gnd you check the wx and after take off it keeps aprox the same.
Prior to descent you scan the area but at low altitudes , even working with tilt up &/or gain it saturates more easily.

My apologies if I did not understand the question correctly LatPilot. What you were describing just looked to me like a commonly experienced antenna tilt issue. With that theory eliminated I can only speculate as to what's happening with your radar that would cause it to behave as you describe. The best advice I can give is to have mx investigate.

One theory which has played a part in similar problems:

If this happens while descending into warm moist air I might suspect condensation as a possible culprit. Cold soaked radomes, antennas and wave guides can collect enough moisture to cause radar problems under some circumstances. Additionally older radomes sometimes entrain moisture in voids created by material delamination. Continued temperature cycles usually make the problem worsen with time as entrained water freezes and furthers the delamination.

Or it could be something else entirely!

Thanks Westpilot!
I liked that theory 'bout condensation at warmer levels, since this happens to me on different airplanes/radars.
Cold soaked radomes/antennas before beginning the descent is usually my scenario. Never came to my mind that possibility!!:ugh:
Regards
LatPilot

What types of airplanes are you flying? A 7xx has a much different radar from a KingAir.

GB

E190, but noticed the some thing flying other jets!!!
:ooh:

I mean the "same" :bored:

Same problem here in the md80. I also suspect moistin radome.

Rate of climb vs. rate of descent will affect how quickly the picture changes, but won't affect the look of the return.

Is there any chance you turned up the gain at altitude, and didn't return it to CAL on descent?

GB

Obviously the rate of descent is higher than the rate of climb in the jets that I flew, but as you said it doesnot has to be related to this.(since we are not talking about a pattern change)

As I said initially I work with the: Tilt, Range,Gain,RCT, etc. but once it saturates it becomes impossible to get a clear picture.

And this ocurrs at low altitude after descent, that why I put more weight on the coldsoaked antena theory!!!
:p

Sorry, I overlooked your second post. Yes, ice can cause funny returns, but you should see false targets at altitude, too, in that case. Have you ever put your hands on the radome after landing, to check temperatures? An IR thermometer would be a neat device to have for this.

What does Maintenance say or do? Is the R/T in the radome behind the antenna, vs. in the pressurized E/E bay? It could be reacting to condensation forming on its parts, from being very cold, descending into warm, moist air. It should be immune to that.

GB

The E-Jets will have new Honeywell integrated Antenna drive, R/T and processor units. It's all a one piece deal called an RTA. No waveguides snaked through bulkheads anymore.

Once upon a time I used to perform maintenance activities on a number of different airline and business airplane types equipped with the older style Bendix or Sperry/RCA systems. This occasioned the removal and installation of many RTs and antenna drives. Getting the waveguide perfectly aligned and secured was essential to preventing moisture ingress and other installation induced problems. Improperly installed waveguide filters, mating flange seals and saturated dessicant were often related to wx radar discrepancies. Poor radome condition is another leading factor in various radar performance issues.

Later, when I began flying with these systems I noted a correlation between moist conditions and an increase in display "fuzz" or "noise". When I began flying somewhat newer airplanes equipped integrated EFIS panels and modern radar, I noticed the same thing, but to a somewhat lesser degree. Better noise filtering, sensitivity/gain control or other display processing functions on the newer units perhaps? Better protection against moisture ingress? All of the above? Probably!

In my experience, the appearance of the anomalous "noisy" returns seems to occur most noticeably when there is little or no precipitation returns being displayed and when descending into moister air. When areas of moderate or greater returns are displayed, the fuzz is less apparent and does not seem to interfere with the display of legitimate returns. So in my personal experience using the radar, it's never really been worthy of a written discrepancy. I've asked avionics techs about it informally and they haven't come up with anything more definitive than what I have. One old Westwind I used to fly had some serious radar issues, but they were the least of the that airplanes problems!

Other than that, even older wx radar usually seems to work well enough in spite of some distracting anomalies. The new stuff is fantastic and getting better all the time.

I hope I can help a little bit!

WX radar beams are not flat, they are however cone shaped.

Also, the smaller the radar antenna, the wider this beam is.

As an example, a flat plate 29" antenna on a B737NG will produce a 3.4º beam.

This may seem very little, however draw a couple of right angled triangles and you will see that there even if your antenna is pointing upwards, you may get some ground clutter.

WX radar beams are rather like that of a torch. Try it out, point a torch a a wall in a dark room. The closer you get to the centre of the beam, the more intense the light is, right?

Back to the 737 radar...... In just 1º of beam, you will fling out 60% of the energy. This means that only 39.9% of the remaining energy is spread out in the remaining 2.4º of the beam. (0.1% is energy that is lost in the process).

However, what is more reflective than a drop of water? Exactly, solid stuff like buildings, trees etc..... So, even though very little energy is giving such building a sun tan, most of that energy bounces off and returns.

So there you have a couple of simple and true reasons which I hope have helped you to figure out what is going on with you WX radar.

Fly safe. Avoid those CBs!




Alberto