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Poseidon-3C: a nadir altimeter in the continuity of the Jason series

The Poseidon-3C, supplied by Cnes derives from the altimeters on Jason-3. It allows to measure the range (the distance from the satellite to the Earth's surface), wave height and wind speed in two different frequencies (Ku- and C-band). It provides with a classical nadir altimeter measurements to calibrate and complement KarIn, in continuity with previous satellites.

A heritage Nadir Payload

Poseidon-3C is derived from the Jason-3 Poseidon-3B altimeter. It is a compact, low-power, low-mass instrument offering a high degree of reliability. Poseidon-3 is a radar altimeter that emits pulses at two frequencies (13.6 and 5.3 GH) and analyzes the return signal reflected by the surface.
It implements an "open loop tracking mode", allowing better retreival of inland water measurements.


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


Radar altimeters permanently transmit signals to Earth, and receive the echo from the surface (see how altimetry works for details). Poseidon-3C 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-3C, 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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