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RE: Analysis from a JHU CS Prof
From: Mikael Abrahamsson <swmike () swm pp se>
Date: Thu, 13 Sep 2001 23:56:29 +0200 (CEST)

On Thu, 13 Sep 2001, Hire, Ejay wrote:

Most ATC towers do not have true radar.  I.e. the ability to detect flying
objects above altitude x by bouncing radio waves off of the object and
computing the time vs. Doppler shift vs. inclination to determine

In modern (non-military) atc systems, this info is relayed by the
transponder to atc.

If true, this is a weird practice. In Sweden, there are several civilian
radars that are true radars with transponder receivers mounted on them as
a compliment.

Having served in the Swedish Airforce and actually having access to
information provided by both civilian and military radars, my experience
is that as long as you're flying fairly high (ie several thousand feet)
even the civilian radars are going to see you fairly far away. Yes, your
transponder is visable long before that, but if you turn it off you'll
still be visable. We received information from both the transponder and
actual civilian radar on our screens and most of the time the civilian
traffic including small props were visable as both transponder
position/hight and radar echo.

What might be the case is that the true radar echo information is not
relayed to the individual ATC because even the civilian high altitude
radar gets cluttered by false echos.

The military low-altitude costal radars are the ones really cluttered.
Man, if it was like in the movies with a beep each time the radar swept an
echo, all military radar officers would be deaf :)

Mikael Abrahamsson    email: swmike () swm pp se

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