Global Calibration of SARAL/AltiKa Using Multi-Mission Sea Surface Height Crossovers

Abstract

SARAL/AltiKa completed its first year in orbit in March 2014. The 1 Hz GDR-T data of the first 10 cycles of the mission are used to perform a comprehensive quality assessment by means of a global multi-mission crossover analysis. Within this approach, SARAL sea surface heights are compared with data from other current missions, mainly Jason-2 and Cryosat-2, to reveal its accuracy and consistency with the other altimeter systems. Alongside with global mean range bias and instrumental drifts, investigations on geographically correlated errors as well as on the realization of the systems origin are performed. The study proves the high quality and reliability of SARAL. The mission shows only a small range bias of about −5 cm with respect to Jason-2 and neither significant time-tag bias nor instrumental drifts. With 1.3 cm the scatter of radial errors is in the same order of magnitude as for Cryosat-2 and Jason-1 GM and will probably further improve using an enhanced sea state bias (SSB) model. However, the wet tropospheric corrections from SARAL radiometer still show some systematic effects influencing the range bias as well as geographically correlated error patterns and the z-component of the origin. Improved inflight calibration will be necessary to overcome these effects.

Keywords:

• SARAL/AltiKa
• calibration
• multi-mission
• crossover differences

Acknowledgements

We would like to thank CNES/ISRO and AVISO for SARAL mission maintenance and data dissemination. Moreover, we gratefully acknowledge ESA and AVISO for providing the other mission data used for cross-calibration and the DAC corrections.