Poseidon-2 being integrated on Jason-1 (Credits Cnes/Alcatel)

The Poseidon-2 altimeter is the main instrument on the Jason-1 mission. Derived from the Poseidon-1 altimeter on Topex/Poseidon, it measures sea level, wave heights and wind speed. It operates at two frequencies and is also able to estimate atmospheric electron content.




Poseidon-2 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-2 operates at two frequencies (13.6 GHz in the Ku band and 5.3 GHz in the C band) to determine atmospheric electron content, which affects the radar signal path delay. These two frequencies also serve to measure the amount of rain in the atmosphere.

Technical data

Poseidon-2, or SSALT (for Solid State ALTimeter), uses solid-state amplification techniques.

Emitted Frequency (GHz)Dual-frequency (Ku, C) - 13.575 and 5.3
Pulse Repetition Frequency (Hz)2060 interlaced {3Ku-1C-3Ku}
Pulse duration (microseconds)105
Bandwidth (MHz)320 (Ku and C)
Antenna diameter (m)1.2
Antenna beamwidth (degrees)1.28 (Ku), 3.4 (C)
Power (W)7
Specific featuresSolid-State Power Amplifier.
Dual-frequency for ionospheric correction,
High resolution in C band (320 MHz)


On the tracks of Topex/Poseidon

The design of Poseidon-2 has been enhanced in several areas. In particular, a second frequency has been added in the C-band for ionosphere corrections, sampling has been improved, and digital components have replaced analog circuits wherever possible.

Design life3 years (operating 5% of time) 5 years (operating permanently)
Mass25 kg2x25 kg (backup)
Antenna mass 8 kg
Power consumption 50 W70 W (C and Ku bands)
telemetry rate (all waveforms)14 kbits/s22 kbits/s
Reliability (target) >0.95
Central frequency13.65 GHz13.575 GHz
Chirp bandwidth320 MHz320 MHz
Chirp duration0.1 ms0.1056 ms
Pulse repetition frequency1700 Hz6Ku/1C: 1800 Hz±10%
4Ku/1C: 1680 Hz±10%6Ku/1C: 300 Hz±10%
4Ku/1C: 420 Hz±10%
Antenna gain44 dB42 dB
Emitted peak power5 W7 W
Pulse number NIMP (50 ms cycle)856Ku/1C: 90
4Ku/1C: 846Ku/1C: 15
4Ku/1C: 21
Sample number (FFT)64128
Fine altitude correction (CFA)1/161/64