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#11
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ATC Radar Question
"Bob Noel" wrote the elevation radar determines altitude the same way the azimuth radar determines bearing. There are actually two radars running for PAR, right? One sweeping left to right and one sweeping up and down, I think. -- Jim in NC |
#12
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ATC Radar Question
Stealth Pilot wrote:
Mode C only provides 100 foot altitude resolution. bzzzzt! Mode C provides a height eg 1252ft which is deemed only accurate to 100ft because the calibration errors are limited to 100ft. I believe that Mode C provides 100 foot altitude resolution because the least significant bit is 100' |
#13
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ATC Radar Question
"Jackie" wrote in message ... Matt Barrow wrote: "Jackie" wrote in message ... I understand that ATC radar uses an encoding altimeter and a transponder operating with Mode C to determine an aircraft's altitude. Let's forget about Mode C for a moment and switch to Mode A only or just a primary return. If an aircraft is at 18,000 ft (approx 3 nm) and 3 nm away from the radar antenna, as seen on a map, how does the radar correct for slant distance when distance is displayed (e.g. using concentric circle distance markers on the scope or relative to a known distance, such as a marker on the display)? In other words how does the radar know that the aircraft is actually 3 nm away laterally and not 4.25 nm (approx slant distance at that altitude)? Asquared + B squared = C squared, I'd guess. And how does it separate A and B? "A" is the radar range, "B" is garnered from the encoding altimiter. |
#14
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ATC Radar Question
"Jackie" wrote in message
... Jim Logajan wrote: Jackie wrote: If an aircraft is at 18,000 ft (approx 3 nm) and 3 nm away from the radar antenna, as seen on a map, how does the radar correct for slant distance when distance is displayed (e.g. using concentric circle distance markers on the scope or relative to a known distance, such as a marker on the display)? Without altitude information from the pilot or a Mode C transponder, the radar system can't extract the horizontal distance from the slant distance. Where did you read that their systems correct for altitude without Mode C transponders? I don't believe I indicated I read this. If they could do that then they wouldn't have ever needed the transponders to report altitude. Does precision approach radar require a transponder to report altitude? At the altitudes involved during approach, it's not so critical (altitude is, but not the angle), but during approach the heading data is as critical as the altitude reporting. |
#15
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ATC Radar Question
"Stealth Pilot" wrote in message
... On Fri, 12 Jun 2009 03:54:29 +0000 (UTC), Clark wrote: Jackie wrote in : [snip] Does precision approach radar require a transponder to report altitude? PAR uses a height finder radar to provide sufficient vertical resolution for precision approaches. Mode C only provides 100 foot altitude resolution. bzzzzt! Mode C provides a height eg 1252ft which is deemed only accurate to 100ft because the calibration errors are limited to 100ft. And when local BARO is not available, the minimums go up. And why the slop (calibration error) is taken into account when developing the approach procedure. |
#16
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ATC Radar Question
"Matt Barrow" wrote in message
... "Jackie" wrote in message ... Matt Barrow wrote: "Jackie" wrote in message ... I understand that ATC radar uses an encoding altimeter and a transponder operating with Mode C to determine an aircraft's altitude. Let's forget about Mode C for a moment and switch to Mode A only or just a primary return. If an aircraft is at 18,000 ft (approx 3 nm) and 3 nm away from the radar antenna, as seen on a map, how does the radar correct for slant distance when distance is displayed (e.g. using concentric circle distance markers on the scope or relative to a known distance, such as a marker on the display)? In other words how does the radar know that the aircraft is actually 3 nm away laterally and not 4.25 nm (approx slant distance at that altitude)? Asquared + B squared = C squared, I'd guess. And how does it separate A and B? "A" is the radar range, "B" is garnered from the encoding altimiter. Interesting thread! But, for the life of me, I can't figure any reason that atc would really care about the exact map location of an aircraft--especially when it is both close enough and high enough for the error to be significant. Given the two most common uses, surveilance approaches to an airport at nearly the same elevation as the radar and collision avoidance, the map distance should be a trivial issue. Peter |
#17
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ATC Radar Question
"Peter Dohm" wrote in message
.. . "Matt Barrow" wrote in message In other words how does the radar know that the aircraft is actually 3 nm away laterally and not 4.25 nm (approx slant distance at that altitude)? Asquared + B squared = C squared, I'd guess. And how does it separate A and B? "A" is the radar range, "B" is garnered from the encoding altimiter. Interesting thread! But, for the life of me, I can't figure any reason that atc would really care about the exact map location of an aircraft--especially when it is both close enough and high enough for the error to be significant. Given the two most common uses, surveilance approaches to an airport at nearly the same elevation as the radar and collision avoidance, the map distance should be a trivial issue. Given the effort put into the significantly more accurate WAAS infrastructure, I'd suspect that getting a more accurate fix would be correspondingly desirable. |
#18
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ATC Radar Question
Jackie wrote:
I understand that ATC radar uses an encoding altimeter and a transponder operating with Mode C to determine an aircraft's altitude. Let's forget about Mode C for a moment and switch to Mode A only or just a primary return. If an aircraft is at 18,000 ft (approx 3 nm) and 3 nm away from the radar antenna, as seen on a map, how does the radar correct for slant distance when distance is displayed (e.g. using concentric circle distance markers on the scope or relative to a known distance, such as a marker on the display)? In other words how does the radar know that the aircraft is actually 3 nm away laterally and not 4.25 nm (approx slant distance at that altitude)? I am late into the thread. But you are presumably talking about an area surveillance radar. Its fan beam does not typically stick 45 degrees up into the sky. Too wasteful of energy. Another concept to ponder: if its beam WERE able to steer up at 45 degrees or more, what do you think its path would look like on a plan position indicator? (a regular display). You've mentioned its slant range is 4.25 miles at 3 mile distance horizontally. 30 seconds later, it might be overhead: where would it paint in terms of range? Three miles?? A circular range ring at 3 miles, all round the display? :-) Brian W |
#19
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ATC Radar Question
In article ,
Jackie wrote: Does precision approach radar require a transponder to report altitude? No. The beauty of the PAR approach is the aircraft only needs a functioning radio. |
#20
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ATC Radar Question
Brian Whatcott wrote:
Jackie wrote: I understand that ATC radar uses an encoding altimeter and a transponder operating with Mode C to determine an aircraft's altitude. Let's forget about Mode C for a moment and switch to Mode A only or just a primary return. If an aircraft is at 18,000 ft (approx 3 nm) and 3 nm away from the radar antenna, as seen on a map, how does the radar correct for slant distance when distance is displayed (e.g. using concentric circle distance markers on the scope or relative to a known distance, such as a marker on the display)? In other words how does the radar know that the aircraft is actually 3 nm away laterally and not 4.25 nm (approx slant distance at that altitude)? I am late into the thread. But you are presumably talking about an area surveillance radar. Its fan beam does not typically stick 45 degrees up into the sky. Too wasteful of energy. That's interesting. So if what you say is correct, an airport surveillance radar has very little coverage of the area, say at the top of a class B airspace because to cover that high an angle is "wasteful." For example, a VFR plane flying legally just above the B ceiling could very well be out of coverage of the radar that is supposed to be also monitoring another high performance aircraft poking through that ceiling at a high rate of speed. I'm not sure I agree with such an energy saving measure. Another concept to ponder: if its beam WERE able to steer up at 45 degrees or more, what do you think its path would look like on a plan position indicator? (a regular display). You've mentioned its slant range is 4.25 miles at 3 mile distance horizontally. 30 seconds later, it might be overhead: where would it paint in terms of range? Three miles?? A circular range ring at 3 miles, all round the display? My distances where small to keep the math simple for discussion purposes, not to suggest what an actual display would include. Geez. |
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