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Poseidon-3B altimeter

The Poseidon-3 altimeter is the main instrument on the Jason-3 mission. Derived from the Poseidon-1 altimeter on Topex/Poseidon, Poseidon-2 on Jason-1 and Poseidon-3 on Jason-3, it measures sea level, wave heights and wind speed. It operates at two frequencies and is also able to estimate ionospheric electron content.


Poseidon-3 measures range (the distance from the satellite to the Earth's surface), wave height and wind speed.

New features wrt Poseidon-3 onboard Jason-2

This new altimeter implements a mixed mode allowing on-board automatic transitions between the Diode/DEM mode and the acquisition/tracking mode with respect to the satellite position, while Jason-2 altimeter requires a ground telecommand to switch from one mode to the other, thus being much less flexible.

Moreover, Poseidon-3B DEM upload is now possible without mission interruption.


Radar altimeters permanently transmit signals to Earth, and receive the echo from the surface (see how altimetry works for details). Poseidon-3B operates at two frequencies (13.6 GHz in the Ku-band, 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 define if there is rain or not.

Technical data

Poseidon-3B, 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
Redundancy Yes
Specific features Solid-State Power Amplifier.
  Dual-frequency for ionospheric correction,
  High resolution in C band (320 MHz)
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