12 votes

"I can't believe it's not optical!"—How satellites use synthetic aperture radar to see more than they otherwise should

Posted by Kuromantis
Tags: satellites, radio waves, physics, radar, imaging, synthetic aperture, videos, scott manley
https://www.youtube.com/watch?v=u2bUKEi9It4

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Title
Satellites Use 'This Weird Trick' To See More Than They Should - Synthetic Aperture Radar Explained.
Authors
Scott Manley
Duration
16:26
Published
Dec 30 2020

1 comment

  1. spit-evil-olive-tips
    (edited )
    Link
    SAR is awesome, and this is a wonderful explanation. tl;dw / eli5 - bigger radar dishes are better, but it's hard/expensive to build a satellite with a big radar dish. However, a satellite is...

    SAR is awesome, and this is a wonderful explanation.

    tl;dw / eli5 - bigger radar dishes are better, but it's hard/expensive to build a satellite with a big radar dish. However, a satellite is moving so fast that during the time it takes the radar signal to travel down to Earth and bounce back, the satellite has moved an non-negligible distance. You can use this, plus a bunch of complicated math, to pretend you have a much larger radar dish.

    Some napkin math: a satellite in a 500 km orbit (which is fairly typical for these LEO satellites) is travelling 7.6 km/sec (source). The radar beam is travelling 1000 km round-trip, which is 0.0033 light-seconds (source). So the satellite travels 7.6 km/sec * 0.0033 sec = 0.02508 km (roughly 25 meters) in that time.

    5 votes