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Single-Frequency Poseidon Altimeter (SSALT)

NSSDCA ID: 1992-052A-06

Mission Name: Topex/Poseidon
Principal Investigators:Dr. Michel Lefebvre
Principal Investigators:Mr. Lee-Lueng Fu


The French-built "Poseidon" radar altimeter (SSALT) on TOPEX was a small single-channel (Ku-Band; 13.6 GHz) instrument used to measure sea surface height and satellite-sea surface height. Poseidon is a solid-state, low-power, and low-mass instrument of a new design. One of the goals of Poseidon was to provide a test-bed for future spaceborne altimeters that may be flown on the SPOT series of spacecraft, ERS-2 or ESA polar orbiting satellites. The Poseidon altimeter shares the NASA altimeter antenna by operating approximately 12% of the time with the NASA altimeter operating 88% of the time. The altimeter consisted of two packages: the processing and control unit (PCU), and the radio frequency unit (RFU). The Poseidon altimeter sends a pulse generated by a surface acoustic wave generator with a 300 MHz bandwidth and 900 MHz frequency to the sea surface. The pulse was frequency converted to 13.65 GHz after generation. The pulses were amplified before transmission. The received pulses are amplified and an FFT analyzer computed the power spectrum of the signal. The signal is then sent through a microprocessor which performed the waveform computations. The output data is related to the sea state and wind speed. Measurement accuracy is expected to be within 10 cm. The Poseidon altimeter was designed and built by ALCATEL- ESPACE for CNES.

Alternate Names

  • TopexPoseidon/SSALT

Facts in Brief

Mass: 23 kg
Power (avg): 49 W
Bit rate (avg): 1.3 kbps

Funding Agency

  • Centre National d'Etudes Spatiales (France)


  • Earth Science: Atmospheric Dynamics
  • Earth Science: Physical Oceanography
  • Earth Science: Geophysics/Geodesy

Additional Information

Questions and comments about this experiment can be directed to: Dr. Dieter K. Bilitza



NameRoleOriginal AffiliationE-mail
Mr. Lee-Lueng FuTeam LeaderNASA Jet Propulsion
Dr. Michel LefebvreTeam LeaderCentre National d'Etudes Spatiales

Selected References

  • Born, G. H., et al., Topex: Observing the oceans from space, EOS, 65, No. 28, 433-434, doi:10.1029/EO065i028p00433, July 1984.
  • Topex/Poseidon mission description, in 1633-5, Rev. B, JPL D-601, Rev. B, JPL/NASA, Dec. 1985.
  • TOPEX/Poseidon Sci Work Team, Topex/Poseidon science investigations plan, in JPL/NASA, Sep. 1991.
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