AltiKa: a Ka-band altimetry system for operational altimetry during the GMES period
Jacques Verron and The AltiKa Mission Group(1)
38041 Grenoble Cedex,
In partnership with scientific laboratories and industry, CNES has studied the feasibility of a high-resolution ocean topography mission based upon a new class of wide-band Ka-band altimeter in preparation for the post-ENVISAT mission and in order to complement the OSTM/Jason-2 mission.
Altimetry is considered as one of the major elements of the ocean observing system to be made sustainable through the GEOSS (Global Earth Observation System of Systems) and GMES (Global Monitoring of the Environment and Security) programs. The central objective is the retrieval of the ocean mesoscale circulation in global or regional ocean models data assimilation. Moreover, other applications of the mission have been identified: coastal altimetry, continental water studies, ice sheet monitoring, low-rain systems characterization are the main ‘secondary’ objectives identified so far.
The proposed architecture for the Ka-band altimeter is based on the classical deramp technique for pulse compression and takes benefits of Alcatel Space and CNES experience in the development of Poseidon-1, -2 and -3 and SIRAL (European Space Agency Cryosat mission). A bi-frequency radiometer is part of the compact Ka-band payload. Both altimeter and radiometer share the same antenna. Apart from the combined altimeter and radiometer, this payload also consists of a DORIS plus LRA (Laser Retroreflector Array) orbitography system that will ensure a high level of accuracy in terms of orbitography.
The technical feasibility of a coupled altimeter / radiometer AltiKa payload has been demonstrated. The altimeter shall provide sea-surface measurements with a very high accuracy. Improved performances over other types of surface shall also be reached, first thanks to the reduced size of the radar footprint compared to a Ku-band instrument, and second thanks to the implementation of new tracking algorithms. Because an opportunity to embark the AltiKa payload on the OCEANSAT-3 platform has appeared in the frame of a cooperation between CNES and ISRO (Indian Space Research Organization), a delta phase B has started at the beginning of July 2005, with an expected start of the phase C/D during the first half of 2006. The launch of OCEANSAT-3 is presently planned in 2009-2010. This mission would thus be a demonstration of Ka-band altimetry as a complement to the Jason-2 mission. The AltiKa payload on OCEANSAT-3 should then be considered as the post-ENVISAT altimetry gap filler.
The AltiKa Mission Group: P. Bahurel, A. Cazenave, B. Chapron, JF. Créteaux, P. De Mey, J. Dorandeu, L. Eymard, L. Kerleguer, JM Lefevre, B. Legresy, PY. Le Traon, F. Lyard, F. Rémy, N. Steunou, P. Sengenes, E. Thouvenot, J. Tounradre, P. Vincent