SSALT, also called Poseidon-1, has validated the technology of a low-power (49 W), lightweight (23 kg without redundancy) altimeter for future Earth observing missions. It was supplied by the French Space Agency (CNES). It shares the same antenna as the NRA; thus only one altimeter operates at any given time (on Topex/Poseidon it operated about 10% of the time, or one cycle in ten).
SSALT operates at a single frequency of 13.65 GHz (Ku-band). Its measurements give the same geophysical information as NRA’s. However since this sensor uses a single frequency, an external correction for the ionosphere must be supplied (see the DORIS instrument).


Poseidon-1 (Credits CNES/Alcatel)


Poseidon-1 measures range (the distance from the satellite to the Earth’s surface), wave height and wind speed.



The altimeter emits a radar beam that is reflected back to the antenna from the Earth’s surface (see how altimetry works for details). Poseidon-1 operates at a single frequency (13.6 GHz in the Ku band).

Technical data

Poseidon-1, or SSALT (for Solid State ALTimeter), uses solid-state amplification techniques.

Emitted Frequency (GHz) Single-frequency (Ku) – 13.65
Pulse Repetition Frequency (Hz) 1718
Pulse duration (microseconds) 105
Bandwidth (MHz) 320
Antenna diameter (m) 1.5
Antenna beamwidth (degrees) 1.1
Power (W) 5
Redundancy No
Specific features Solid-State Power Amplifier (low power, low mass)

Further information on Topex/Poseidon (Aviso website)