I don't think that altitude from the ModeC is ever factored into where to
plot the target. The target was always slant range.
BT

"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? If they could do that then they wouldn't
have ever needed the transponders to report altitude.

So if a pilot turns his Mode C from off to on, does the radar then correct
the distance plotted (less distance from the antenna) based on the
altitude reported?