CoAuthors

Pascal Bonnefond (OCA/GEOAZUR, France); Stelios Mertikas (Technical University Crete, Greece); K N Babu (Space Applications Center ISRO, India)

Launched in February 2013, the joint Indo-French SARAL mission carries an experimental Ka-band altimeter measurement system (AltiKa) in a 35-d repeat orbit. We present in-situ calibration results from SARAL overflights of (or near) the CNES and NASA prime altimeter verification sites, Corsica and Harvest respectively. While both of these facilities were developed to support monitoring of the reference (Jason-class) missions (10-d repeat orbit), other altimeter missions can benefit from the dedicated infrastructure at these two locations. This is particularly true for the Corsica calibration site, which was expanded regionally (to Ajaccio and Capraia) in order to support monitoring of the Envisat mission. Prior to its 2012 demise, this ESA mission traced out the same 35-d repeat track later inherited by SARAL. While the Harvest infrastructure is concentrated on the platform, regional techniques can be used to connect the SARAL data (on remote ground tracks) to the reference calibration time series. The closest open-ocean approach of SARAL to Harvest is ~18 km along a descending pass. The corresponding data have been used along with mean-sea surface (MSS) corrections to produce estimates of the SSH bias at Harvest.

We combine regional calibration results from the Corsica and Harvest sites to arrive at preliminary, but unified estimates of the SSH bias and drift for SARAL/AltiKa. This provides a unique opportunity to connect SARAL, using common processes and standards, to the 22-yr absolute calibration time series underlying combined Harvest/Corsica record. Results from the Gavdos (Greece) and Kavaratti (India) calibration sites will also been presented.