Picking up from LiDAR
Part 1, video 5 on LiDAR, measured the road in three steps: fire a laser pulse, start the clock, work out the distance. But in thick fog, water droplets scatter the laser everywhere, and the car needs a second eye: radar.
HOW IT WORKS
Long waves slip through fog
Radar measures distance with radio waves. The waves used in cars are almost 4 mm long, about 4,300 times longer than LiDAR's laser. Fog droplets are far smaller than that, so the waves slip right through.
THREE STEPS
The same three steps as LiDAR
Radar follows exactly the same three steps as LiDAR: send a wave, time it, work out the distance. For a car 150 meters ahead, the round trip takes just one millionth of a second.
ONE MORE STEP
Doppler measures speed
Radar's big advantage is measuring speed instantly, thanks to the Doppler effect. Just as an ambulance siren sounds higher as it comes closer, waves bouncing off an approaching object get squeezed together. If the car ahead is 10 meters per second slower, the wave shifts by about 5,000 hertz.
LIMITS
Blurry, and easily fooled
The trade-off: radar sees very blurrily, so it struggles to tell a person from a motorbike or a sign. Metal reflects very strongly, so a can or an overpass can be mistaken for an obstacle.
AROUND YOU
Radar is everywhere
Radar powers adaptive cruise control, blind-spot warnings and weather rain maps.
This article is based on the video How radar helps cars see through fog from the Mark học AI channel. Watch the video (in Vietnamese) to see the animations.
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