Radar altimetry

A technique that bounces a radar pulse straight down and times the round trip to measure the satellite’s exact height above the surface — and from that, the height of the surface itself.

Why it matters

Radar altimeters track sea level rise, ocean currents, and the heights of lakes and rivers with centimeter precision, providing one of the longest and most important records of a warming, rising ocean.

Where you’ll meet it

• Jason series (and its successor Sentinel-6) has measured global sea surface height for decades.
• SWOT uses a wide-swath radar altimeter to map ocean features and inland water in two dimensions.
• TOPEX/Poseidon, an earlier mission, began the modern satellite sea-level record.

In plain terms

It’s like dropping a stone down a well and timing the splash to learn the depth — except the satellite pings the sea below and times the echo to measure its height.