Jason-3 instruments

The Poseidon-3B altimeter

The Poseidon-3B is the mission’s main instrument. It allows measuring the range (the distance from the satellite to the Earth’s surface), wave height and wind speed. 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. Indeed, Jason-2 uses the two altimeter modes, the “autonomous tracking” and the Diode/DEM modes, to improve measurements over coastal areas, inland waters and ice. But these modes have the disadvantage to be exclusive.

 

Poseidon-3B being integrated on Jason-3 (Credits CNES)

 

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.

Technical data

Poseidon-3, or SSALT (for Solid State ALTimeter), uses solid-state amplification techniques.

Poseidon-3B Main parameters
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)

 

The Advanced Microwave Radiometer (AMR)

Developed by NASA, it measures radiation from the Earth’s surface. Each frequency is combined to determine atmospheric water vapor and liquid water content. Once the water content is known, the correction to be applied for radar signal path delays is determined. It performs thorough lesson learned review from Jason-2 experience with: account for parts obsolescence, improve the instrument thermal control and stability, small design updates to retire residual implementation risks on Jason-2. Unlike the radiometers of its predecessors, the calibration of the Jason-3 AMR should be completed with pitch manoeuvres in order to perform cold-space measurements at regular intervals (every 30 to 60 days).

 

Locations systems

 

GPS Receiver (GPSP)

The GPSP uses the Global Positioning System (GPS) to determine the satellite’s position by triangulation, in the same way, that GPS fixes are obtained on Earth. At least three GPS satellites determine the mobile’s exact position at a given instant. Positional data are then integrated into an orbit determination model to track the satellite’s trajectory continuously.

Supplied by NASA, it is a different receiver but with same basic (blackjack) design as on Jason-1 and 2. No changes to data processing or products with expecting same or better performance as on Jason-2.

DORIS (Doppler Location)

The Doris system uses a ground network of 60 orbitography beacons around the globe, which send signals at two frequencies to a receiver on the satellite. The relative motion of the satellite generates a shift in the signal’s frequency (called the Doppler shift) that is measured to derive the satellite’s velocity. These data are then assimilated in orbit determination models to keep permanent track of the satellite’s precise position (to within three centimeters) on its orbit.

This instrument is supplied by Cnes with a new generation (DGXXS) taking into account lessons learned from Jason-2. Improvement in modelling solar panels position has been made. Model improvements have been integrated: albedo and infra-red pressure, new ITRF, pole prediction, Hill along-track empirical acceleration, on-board USO frequency prediction,  allowing a more and more accurate Diode navigation tool.

LRA (Laser Tracking)

The LRA instrument, provided by NASA, is an array of mirrors that provides a target for laser tracking measurements from the ground. By analyzing the round-trip time of the laser beam, the satellite’s orbit location can be determined.

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