Radar Altimeter 2 (RA-2) is an instrument onboard the ENVISAT satellite for determining the two-way delay of the radar echo from the Earth's surface to a very high precision: less than a nanosecond. It also measures the power and the shape of the reflected radar pulses.

It is a nadir-looking pulse-limited radar altimeter based on the heritage of ERS-1 RA functioning at the main nominal frequency of 13.575 GHz (Ku Band), which has been selected as a good compromise between the affordable antenna dimension that provides the necessary gain and the relatively low attenuation which experience the signals propagating through the troposphere.