Level1b Performance Evaluation on CryoSat Products
Scagliola, Michele1; Fornari, Marco2; Tagliani, Nicolas1

The main payload of CryoSat is a Ku-band pulse width limited radar altimeter, called SIRAL (Synthetic interferometric radar altimeter), that transmits pulses at a high pulse repetition frequency thus making the received echoes phase coherent and suitable for along track processing. This allows to reach a significantly improved along track resolution with respect to traditional pulse width limited altimeters.

SIRAL is capable of operating in three measurement modes: low resolution mode (LRM), Synthetic Aperture Radar (SAR) and Synthetic Aperture Radar Interferometric (SARIn). Even if the Level 1b products are defined depending on the operating mode, all the Level 1b products consist essentially of a calibrated waveform for each point along the ground track of the satellite with a data record rate of about 20 Hz.

In this poster we will compare the Level1b performance specification with the effective performance as they are measured on the Level1b products, focusing on the impulse response functions and the signal-to-noise ratio.
For what concerns the impulse response functions in the along track and in the across track direction, the main figures of merit such as the resolution and the peak-to-side lobe ratio will be discussed and it will be shown that the performance are in line with expectation. Moreover it will be shown as the performance have been proven to be stable over almost 3 years of mission.
Then, the signal-to-noise ratio measured on the Level1b waveforms will be presented. In particular, it will be discussed the effect of the hamming weighting on the signal-to-clutter-noise for the SAR/SARIn waveforms over ocean. In fact the hamming weighting, that has been introduced in the along track processing to suppress the nadir clutter caused by specular surface as the sea ice, allows to minimize the clutter also on the SAR/SARIn waveform over ocean, leading to an increase of signal-to-clutter-noise power ratio equal to about 4 dB.