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RE: Analysis from a JHU CS Prof
From: "Leigh Anne Chisholm" <lachisho () tnc com>
Date: Thu, 13 Sep 2001 16:18:46 -0600


I can't speak for the US, but in Canada we definitely have an abundance of
"true radar" installations in most non-military control towers.  I don't
know the number of times I've heard tower indicating that they have an
aircraft out in the practice area--keep an eye out.  Altitude is unknown.
That's just the standard advisory control tower's radar - and not the large
area control centre radar.  Canada has 7 area control centres for Canada and
the Territories, and one "advisory" tower for each ATC centre at each
airport.  Edmonton for example, has two "advisory" towers - one for the
Municipal airport, one for the International airport slightly to the south
of the city.

Ejay, you did make me wonder about your comments.  I've sent off an Email to
Nav Canada.  If I get a response as to how the radar in Canada operates,
I'll share it with you.



-----Original Message-----
From: owner-nanog () merit edu [mailto:owner-nanog () merit edu]On Behalf Of
Mikael Abrahamsson
Sent: Thursday, September 13, 2001 3:56 PM
To: nanog () merit edu
Subject: RE: Analysis from a JHU CS Prof



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
altitude/heading/speed.

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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