WX Radar Secondary Lobe and Ghost Echo
 

This is a report from a different PP forum; I believe that you Tech' fans are familiar with this phenomenon but this is a more specific question reg Auto/Man Modes on a Weather Radar:

It seems that when on Auto mode, the side lobe that produces the false echo at a pseudo distance equal to the height of the aircraft is removed, whereas in Manual mode, it is not.
Could someone explain if this makes sense and if yes why ? I.e. what would be the difference in Auto mode regarding de cluttering of the return of the side lobe as opposed to Man mode?

Also, the false echo seems to get worse if the radome is wet, or in bad shape, or covered with ice, or not fully adjusted correct?

What could be done to remove or diminish this phenomenon, even on a brand new aircraft ?

Thanks a lot,
Leo

False echos resulting from defects, damage, ice build-ups, etc on the radome are easy to detect. They'll appear as unusual displays of weather (odd shapes, etc) but will remain at fixed distances on the display at all times. In other words, during flight they will not move towards you.

Most of the time these types of echos are caused by incorrect radome repairs and, believe it or not, using the wrong paint or glue for touch-ups and repairs.

Manual over Auto. Depending on the radar unit itself, the use of Manual over Auto can cause/change all sorts of variations on the display. In a typical (conventional) radar unit, manual simply removes the calibration feature and turns you into the engineering genius. Normally, this results in far more energy to, then received back from the target, then should really have been used. However, this is not always the case. There is also a correlation between the OAT & Flight level, and the selected level of gain. So, the results on the display when in manual mode are rarely accurate. This increase in energy explains the phenomena that you ask about.

Most people would use manual to find the 'least worst' path through and area of extensive weather, however, there is far better and safer method whereby you'd leave the unit it Auto, select the correct tilt, and then analyze the weather returns, the ground returns, and the attenuation shaddows. This method is much more accruate.

I wrote a Weather Radar training manual several years ago. If you'd like a copy, send me your email address and I'll send you one.

Also, I PM'd 'pantload' as he's quite knowledgable on this subject. Let's see what he says.