Radar Altimeter 2 (RA-2) was an instrument on board the Envisat satellite, which determined the two-way delay of the radar echo from Earth's surface to a very high precision: less than a nanosecond. It also measured the power and the shape of the reflected radar pulses.
The RA-2 instrument was a dual-frequency, nadir-pointing, pulse-limited radar operating at 13.575 GHz (Ku-band) and 3.2 GHz (S-Band) using a single antenna dish and was based on the heritage of the ERS-1 RA. It was designed to operate autonomously and without interruption over all surfaces: ocean, land and ice. RA-2 was the first high-latitude altimeter that aimed to improve the precision of previous altimeters over open oceans (ERS satellites), enhancing operations over ice sheets.