AltiKa Altimeter: Instrument Description and In Flight Performance

Abstract

On 25 February 2013, the SARAL satellite was launched from the Indian Sriharikota launch site. The key feature of the altimetric payload has been the selection of Ka-band. Using Ka-band avoids the need for a second frequency to correct for the ionosphere delay and eases the sharing of the antenna by the altimeter and the radiometer. The use of the Ka-band also allows the improvement of the range measurement accuracy in a ratio close to 2 due to the use of a wider bandwidth and to a better pulse to pulse echo decorrelation. Eventually, Ka-band antenna aperture is reduced, which limits the pollution within useful ground footprint. A summary of the results obtained during the in-flight assessment phase is given. All the tracking modes have also been gone through. Eventually, a new high data rate mode, called “HD mode” is implemented on AltiKa and has been used. The performance assessment is excellent: the range measurement accuracy is close to 1 cm for 1s averaging and the Significant Wave Height (SWH) noise is less than 5 cm (for a 2m SWH at 1?). The tracking success is close to 100% over oceans and 96% over all surfaces.

• Keywords Altimetry
• retracking
• Ka-band
• tracking

Acknowledgements

The work presented in this paper involved a large team who has been contributing through the AltiKa development, ground tests, and assessment phase analysis: CNES, ISRO, CLS, TAS-F, Astrium, all involved people have made years of efforts.

The authors would like to particularly thank the Thales Alenia Space AltiKa team, notably Benoit Durand, Frédéric Robert and Vincent Adrian for the development and validation of the altimeter. The authors are grateful to Jean-Christophe Poisson and to others CLS investigators for the CALVAL activities. CLS has also provided inputs and figures included in this paper.