eli5: how is it possible to fly below radar (per movies)?
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Radar works by bouncing electromagnetic pulses off of objects. The radar systems more or less need a straight line of “sight” to the target to see it. Natural geologic formations or the curvature of the earth itself can break up that line.
Most radar is line of sight. With the radar tower elevated it can have line of sight to the horizon. For the most part you really couldn’t unless the terrain was rough enough to obstruct the line of sight to the tower. Perhaps a very mountainous area. But in flat terrain it would pretty much be impossible.
Few ways.
Radar works by sending our electromagnetic waves, the waves bounce off the plane(or any object, which is important here) and are then received by an antenna that can use some math and electronics to figure out what’s out there.
Common analogy is like an invisible flashlight and only being able to see the light shines back with special lenses.
If the radar is from an earlier model and on a plane, it has a hard time to determine whether or not the object bellow it is the ground, or a plane.
If radar plane is above the target plane, all it would see is the ground since everything bounces off the ground.
This has been pretty much eliminated with modern radar with look down/ shoot down capabilities.
From ground based radar, there can be things in the way. [ Houses, the curve of the earth, mountains, trees, etc. ](https://qph.cf2.quoracdn.net/main-qimg-73c7e756a4ec9dcf64eb4384be7e5cc1)
these can all interfere with the radar’s ability to track a plane.
There’s also other minutiae about different search patterns and avoiding search radar vs tracking or guidance radar but that’s getting into the weeds a bit.
If the flight planners knows where the search radars are situated they can map out a path that keeps the plane “masked” by terrain features.
Tactical aircraft are usually equipped with RWR gear (that’s Radar Warning Receiver). The RWR will alert the pilot when their aircraft is being “painted” by a radar. The newer RWR gear will identify the type of radar, and display a bearing to it. RWR systems pick up airborne radar threats as well as land-based and the pilot can alter course to avoid detection.
Stealthy planes can improve their survivability by keeping their “low observable” side pointed toward the threat radar in hopes of it being undetectable.
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