Tuesday, February 26, 2013

SARAL/AltiKa to enhance understanding of Earth’s climate

radar altimetry
Altimeters emit signals to Earth, and receive the echo from the sea surface, after its reflection.
The sea height is represented by the distance satellite - surface and the satellite's position relative to an arbitrary reference surface (the reference ellipsoid).
Some location systems like Doris enable to determine the satellite's position at a high accuracy.

We have also to take into account the disturbance suffered by the wave radar.
The measurement of these disturbances (by others instruments, or by using multiple frequencies), or their estimation with models, can correct the altimetry measurement. 


The French-Indian SARAL/AltiKa altimetry mission has been launched yesterday from the Satish Dhawan Space Centre in southern India.
Its goal is to enable closer monitoring of sea-surface height from space.

SARAL/AltiKa: A French-Indian mission for the monitoring of the environment : Altimetry (AltiKa) and contribution to ARGOS system

The SARAL/AltiKa project is a collaboration between France and India in the environment monitoring domain.
On a platform developed by the indian space agency (ISRO), two independant payloads will be embarked, ARGOS-3 and AltiKa (+DORIS, +LRA), but their missions have the save objective: to promote the study of the environment from space.

ARGOS-3 is an element of the ARGOS system, dedicated to localisation, acquisition and distribution of environmental data.
AltiKa is an innovating Ka-band altimeter system, dedicated to accurate measurement of ocean surface topography.
It is envisioned as a successor of RA-2 instrument on board ESA's satellite ENVISAT.

The AltiKa project is part of a French program of operational oceanography development including notably the deployment of in situ measurements (CORIOLIS project) and the implementation of an analysis and forecasting center (Mercator Ocean).
These two programmes are the French contribution to GODAE (Global Ocean Data Assimilation Experiment), first international operational oceanography experiment.
Thanks to the work of the French and international community, diverse applications of modeling/assimilation systems such as Mercator Ocean are in operation to begin to answer the scientific needs as well as civil or defense operational applications.

Characteristics :
  • IMS-2 Platform (Small Satellite Bus) developed by ISRO
  • CNES/ISRO Collaboration
  • Altimetric payload: an altimeter-radiometer (AltiKa), Doris and a laser reflector for precise orbitography; ARGOS payload: Argos-3 instrument.
  • Measurement of ocean surface topography, surface wind speed, surface wave height.
    Contribution to ARGOS system continuity for collect and distribution of environmental data.
  • High inclination orbit at 800 km altitude
  • Mission lifetime: 5 years for Argos, 3 years for AltiKa
Altimetry is a key observation parameter of the system and continuity of observations is a critical factor of its efficiency.
A participation to the permanent observation system that will feed operational oceanography thus constitutes a major objective of AltiKa.
The definition and implementation of the Marine Core Service of the GMES program within the MyOcean2 project (in the continuity of the MERSEA project), gives even more importance to this goal.

The data processing will be integrated to the CNES ground segment "SALP" (Système d'Altimétrie et de Localisation Précise), which already operates the altimetry missions Topex/Poseidon, Jason-1, Envisat, GFO, and Jason-2.
SARAL/AltiKa will fly on the same orbit than ENVISAT, to ensure a continuity of altimetry observations in the long term.
On the other hand, the local time of passage over the equator will be different due to specific cover requirements for the instruments constellation of ARGOS system.

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