SRAL : Validation of Performances on EM and PFM Models
Le Roy, Yves¹; Deschaux-Beaume, Marc¹; Houpert, Alexandre¹; Mavrocordatos, Constantin²; Borde, Franck^2
1THALES ALENIA SPACE, FRANCE; ²ESTEC, NETHERLANDS

Developed in the frame of the Global Monitoring for Environment & Security (GMES) initiative, SRAL, the radar altimeter instrument of the Sentinel-3 topography mission, aims to provide not only Sea Surface Height (SSH) and Significant Wave Height (SWH) measurements over ocean and coastal zones but also range measurements over sea ice, ice sheets and in-land waters.

The SRAL measurement modes include two radar modes consisting of :
· the conventional Low Resolution Mode (LRM) as for the ENVISAT/RA-2 and JASON/Poseidon instruments,
· the SAR mode allowing enhanced resolution along-track as for the CRYOSAT/SIRAL altimeter currently in operation.

Each radar mode is operated either in a closed-loop tracking fashion (autonomous tracking of the ground echo) or in an open-loop fashion by using a priori knowledge of the satellite height and of the terrain elevations. Direct transitions are implemented in order to minimise the transition times between two modes. The SRAL mode diagram including the measurement and the calibration modes will be presented.

The validation of SRAL performances was first carried out on the Engineering Model (EM). The characteristics obtained on this model, such as the Range & Azimuth Impulse Responses, the receive transfer function and the range accuracy, will be reviewed as well as the validation of the tracking performances in Closed-Loop and Open-Loop with the associated scenarios.

The performance validation is being completed on the SRAL Proto-Flight Model (PFM) for which testing is on going and should be completed by half-2103. The results obtained on the two chains (nominal / redundant) of the SRAL PFM will be presented in details in this paper.

Bibliography:

[1] Mavrocordatos C., Berruti B., Aguirre M., Drinkwater M., The Sentinel-3 mission and its topography element, 2007, IGARSS-07 Proceedings, Barcelona, Spain

[2] Le Roy Y., Deschaux-Beaume M., Mavrocordatos C., Aguirre M., Hélière F. SRAL SAR Radar Altimeter for Sentinel-3 mission, 2007, IGARSS-07 Proceedings, Barcelona, Spain

[3] Le Roy Y., Deschaux-Beaume M., Mavrocordatos C., Borde F. SRAL, a radar altimeter designed to measure a wide range of surface types, 2009, IGARSS-09 Proceedings, Cape Town, South Africa

[4] Le Roy Y., Deschaux-Beaume M., Mavrocordatos C., Borde F. SRAL, a radar altimeter designed to measure several surface types, SPIE-2010, Toulouse, France

[5] Le Roy Y., Deschaux-Beaume M., Mavrocordatos C., Borde F. SRAL latest results on EM and PFM models, OSTST-2012, Venice, Italy