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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.

  Poseidon-1 Poseidon-2
Design life 3 years (operating 5% of time) 5 years (operating permanently)
Mass 25 kg 2x25 kg (backup)
Antenna mass 8 kg
Power consumption 50 W 70 W (C and Ku bands)
telemetry rate (all waveforms) 14 kbits/s 22 kbits/s
Reliability (target) >0.95
  Poseidon-1 Poseidon-2  
Ku-Band Ku-Band C-Band
Central frequency 13.65 GHz 13.575 GHz 5.3 GHz
Chirp bandwidth 320 MHz 320 MHz 320 MHz or 100 MHz
Chirp duration 0.1 ms 0.1056 ms 0.1056 ms
Pulse repetition frequency 1700 Hz 6Ku/1C: 1800 Hz±10%  
4Ku/1C: 1680 Hz±10% 6Ku/1C: 300 Hz±10%    
4Ku/1C: 420 Hz±10%      
Antenna gain 44 dB 42 dB 33 dB
Emitted peak power 5 W 7 W 16 W
Pulse number NIMP (50 ms cycle) 85 6Ku/1C: 90  
4Ku/1C: 84 6Ku/1C: 15    
4Ku/1C: 21      
Sample number (FFT) 64 128 128
Fine altitude correction (CFA) 1/16 1/64 1/64
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