Data Quality Assessment of the SARAL/AltiKa Ka-band Mission
Picot, Nicolas¹; Guillot, Amandine¹; Sengenes, Pierre¹; Noubel, Jocelyne¹; Steunou, Nathalie¹; Valladeau, Guillaume²; Philipps, Sabine²; Ablain, Michael^2
1CNES, FRANCE; ²CLS, FRANCE

SARAL (Satellite for ARgos and ALtika) is a satellite mission mainly dedicated to ocean environment monitoring, developed jointly by CNES and ISRO (Indian Space Research Organization). Its payload consists in an ARGOS instrument, and an altimetry payload including the AltiKa radiometer-altimeter. SARAL/AltiKa fly on the same orbit than the one used by ENVISAT, allowing to continue the long term data monitoring on this ground track.

The AltiKa instrument consists in a Ka-band altimeter and an embedded dual frequency radiometer. Contrary to past altimetric missions which were in Ku/C-band, AltiKa is a single frequency Ka-band altimeter, with an enhanced bandwidth (480MHz w.r.t 320MHz for Poseidon3) providing a better vertical resolution. The spatial resolution is also improved, thanks to the Ka-band (smaller footprint) and the increased PRF (4KHz w.r.t. 2kHz for Poseidon3). This leads to a noise reduction in the 1Hz-data (more echoes averaged).

We will present in this paper the data quality assessment performed on CNES and CLS side, focusing on deep ocean and using classical CalVal analysis tools. This will include mono mission Cross Over analysis, Sea level residuals but also the comparison with the Jason-2 reference mission and the ESA CryoSat mission. A specific focus will be given on the spectral analysis and a comparison to others missions, including the SAR mode on Cryosat mission, will be presented.

The drawback of the Ka-band is the higher sensitivity (w.r.t. Ku-band) to rainy and cloudy conditions, which may lead to data loss and/or degradation, especially in the tropics. We will present the early findings in terms of data degradation, using collocated data with AMSU in order to link the rain rate observed by AMSU mission with the altimeter data quality assessment. This will be illustrated thanks to waveforms degradation, radiometer brightness temperatures and along track data quality compared to multi mission DUACS maps in dedicated areas.