Pascal Bonnefond (Observatoire de Paris - SYRTE, France); Bruce Haines (JPL/NASA, USA); Christopher Watson (University of Tasmania, Australia); Florent Lyard (LEGOS, France); David Cotton (SatOC, UK); Jérôme Benveniste (ESA/ESRIN, Italy)

In situ calibration ensures regular and long-term control of the altimeter sea surface height (SSH) time series through comparisons with independent records. Usually, in situ calibration of altimeter SSH is undertaken at specific CalVal sites through the direct comparison of the altimeter data with in situ data.

However, Noveltis has developed a regional CalVal technique, which aims at increasing the number and the repeatability of the altimeter bias assessments by determining the altimeter bias both on overflying passes and on satellite passes located far away from the calibration site. In principle this extends the single site approach to a wider regional scale, thus reinforcing the link between the local and the global CalVal analyses. It also provides a means to maintain a calibration time series through periods of data-outage at a specific dedicated calibration site.

The regional method was initially developed at the Corsican calibration sites of Senetosa and Ajaccio. It was then successfully implemented at the Californian site of Harvest and at the Australian site of Bass Strait, in close collaboration with JPL and the University of Tasmania, respectively. The method was used to compute the altimeter biases of Jason-1, Jason-2, Envisat and SARAL/AltiKa at all these sites.

These recent studies gave the first Envisat and SARAL/AltiKa absolute bias estimates at non-dedicated sites using the same method, and showed high consistency with the analyses of the global CalVal teams and the work of the in situ CalVal teams. Some new perspectives and possibilities to exploit the technique are now explored with the specificities of the CryoSat-2 mission.