The DORIS instrument onboard Jason-2 provides real-time location and precise orbit determination. DORIS measurements are also used for geophysical studies, in particular through the International DORIS Service (IDS). DORIS is a dual-frequency instrument able to determine atmospheric electron content.

DORIS antenna

The main changes from the previous DORIS instruments are:
– the instrument will benefit from full redundancy;
– it will be possible to fully reload software without any mission interruption;
– platform attitude will be provided in real time to DORIS and used by Diode (the onboard DORIS navigator); and will also be downloaded by DORIS with the science telemetry dataflow;
– a dosimeter will be included in the electronics unit, to measure the total radiation dose received by DORIS;
– the onboard altimeter will receive information from DORIS for real-time tracking.

Function

Real-time location: Diode

The Diode onboard navigator locates the satellite on orbit in real time. This information is essential for providing altimetry data in real time or near-real time.

DORIS network of orbitography beacons and their spatial coverage (Credits IDS

Precise orbit determination

DORIS measurements are used for precise orbit determination (POD).

Ionospheric electron content

By measuring and comparing the path delay of signals transmitted at two separate frequencies, DORIS is able to calculate the electron content in the atmosphere. This information is then used to determine perturbations on the altimeter’s radar signal.
This function complements the dual-frequency altimeter function.

Principle

DORIS orbitography beacons transmit signals at two separate frequencies (2,036.25 MHz and 401.25 MHz) to the satellite. The receiver onboard the satellite analyses the received signal frequencies to calculate its velocity relative to Earth. This velocity is fed into orbit determination models to derive the satellite’s position on orbit to within two centimetres on the radial component.

mvr2

For further information, see the International DORIS Service (IDS) and DORIS, the space surveyor (Aviso)