Satellite technology can provide continuous and precise measurement of sea surface height. These data are used to calculate the speed and direction of ocean currents and temperature-related changes in ocean volume.

This image is from the NASA TOPEX/Poseidon mission which monitored global ocean circulation 1993 to 2005. The mission's most important achievement was determining how heat stored in the ocean moves from one place to another. TOPEX/Poseidon has ceased operations but like many satellites, remains in orbit.

TOPEX was a Nadir-pointing radar altimeter operating at C band (5.3 GHz) and Ku band (13.6 GHz).
Poseidon was a solid state Nadir-pointing radar altimeter that operated at Ku band (13.65 Ghz).