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.