PPRuNe Forums - View Single Post - Air Asia Indonesia Lost Contact from Surabaya to Singapore
Old 14th Jan 2015, 00:03
  #1953 (permalink)  
Ian W
 
Join Date: Dec 2006
Location: Florida and wherever my laptop is
Posts: 1,348
Originally Posted by ACLS65 View Post
It is also things like FTC and STC to reduce clutter and I am sure lots of digital processing now.

"Sensitivity Time Control (STC). This feature reduces the impact of returns from sea state. It reduces the minimum SNR of the receiver for a short duration immediately after each pulse is transmitted. The effect of adjusting the STC is to reduce the clutter on the display in the region directly around the transmitter. The greater the value of STC, the greater the range from the transmitter in which clutter will be removed. However, an excessive STC will blank out potential returns close to the transmitter.

Fast Time Constant (FTC). This feature is designed to reduce the effect of long duration returns that come from rain. This processing requires that strength of the return signal must change quickly over it duration. Since rain occurs over and extended area, it will produce a long, steady return. The FTC processing will
filter these returns out of the display. Only pulses that rise and fall quickly will be displayed. In technical terms, FTC is a differentiator, meaning it determines the rate of change in the signal, which it then uses to discriminate pulses which are not changing rapidly."

Radar Systems


island_airphoto
Anyone who wants to see radar freq. vs. rain can take a look here:
https://www.youtube.com/watch?v=RvTkVj5-uv0
This isn't POWER, it is FREQUENCY.
These approaches will reduce the clutter in the returned signal but they do not change the attenuation of the radar outbound or reflected signal as it passes through rain. If the rain is heavy enough the radar signal will literally not get through. There are things that can be played with like changing the polarization of the radar signal but they don't solve the attenuation problem. An analogy is dense fog - To radar rain is like dense fog you can play with yellow headlights or blue headlights but if the fog is dense enough you will not be able to increase the visibility by a lot.

The approaches suggested in research are variants of multisensor tracking where a complete 4D picture is built up using ground radars. See NSSL Projects: Multi-Radar/Multi-Sensor System (MRMS). These pictures may then be sent to the flight deck through Aircraft Access to SWIM (System Wide Information Management). This is in the Continental United States. It may be that other areas could do the same but it is expensive.
Other approaches have looked at taking all the aircraft radars and mosaicing them into a 4D picture. But again someone has to do it and then find someone willing to pay for it. Guess what the beancounters won't hear of it.
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