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Poseidon-2

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.

 

 

Functions

Poseidon-2 measures range (the distance from the satellite to the Earth's surface), wave height and wind speed.

Principle

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
RedundancyYes
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
Central frequency 13.65 GHz 13.575 GHz
Chirp bandwidth 320 MHz 320 MHz
Chirp duration 0.1 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
Emitted peak power 5 W 7 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
Fine altitude correction (CFA) 1/16 1/64
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