Diode, created by Cnes in 1991, means Détermination Immédiate d'Orbite par Doris Embarqué. It is an integrated software to the Doris instrument that calculates real-time location and very precise velocity of the satellite. Embedded  on Spot 4, Diode team now all satellites since Jason-1. Since Diode was onboard the Spot 4 satellite on an experimental basis, this software fits out all satellites since Jason-1.

Every 10 seconds, Diode runs a program that:

• acknowledges commands;
• predicts the satellite's position using a model of its motion;
• corrects the predicted position on the basis of Doris measurements (when the satellite is within view of a ground beacon);
• and lastly, delivers the calculated position to the ground station.

The real-time orbit is used on the ground to produce Operational Sensor Data Records (OSDRs), which will be generated and distributed within three hours to operational oceanography centers throughout the world.

Further information:

• Precise Orbit Determination (POD), a preliminary orbit from the Diode onboard navigator.
• Newsletter #9, 2003: Doris new Diode navigator and beacon network developments? G. Tavernier et al. (pdf, 1.19 MB).
• Towards centimetre orbits in real time with Doris/Diode, A. Auriol et al., OST/ST'2007 posters (pdf, 225 KB).
• Coupling Doris/Diode with the Poseidon-3 altimeter : a team effort in orbit. C. Jayles et al. (pdf).
• Towards centimetre orbits in real time with Doris/Diode, A. Auriol et al., OST/ST'2007 posters (pdf, 225 KB).