Poseidon-2
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 |
| Redundancy | Yes |
| Specific features | Solid-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 |
Past missions 
