SRAL, A RADAR ALTIMETER DESIGNED TO MEASURE A WIDE RANGE OF SURFACE TYPES

SCOPE In the context of Global Monitoring for Environment and Security (GMES), the objectives of the Sentinel-3 mission driven by ESA encompass the commitment to consistent, long-term collection of remotely sensed data of uniform quality in the areas of sea/land topography and ocean colour. The Sentinel-3 satellite indeed carries a topography mission including mainly RF instruments and an ocean and land colour mission composed of optical instruments. The aim of this paper is to describe the core instrument of the topography mission [1], the SRAL radar altimeter [2], and its latest development steps. OVERVIEW OF SRAL MISSION REQUIREMENTS The SRAL (Sar Radar ALtimeter) instrument is not only specified to retrieve the classical parameters used in the oceanography field such as the Sea Surface Height (SSH), the Significant Wave Height (SWH) and the sea wind speed but it also makes it possible to perform range measurements over the following surfaces: Sea ice Ice sheet interiors (e.g. Antartic plateau) Ice margins In-land waters To achieve these objectives, SRAL will be supported by the other elements of the topography payload : A microwave radiometer which corrects for the tropospheric delay; A real-time navigation system implemented by a GPS equipment; A Laser Retro-Reflector Assembly to provide calibration of range measurements. The SRAL mission requirements and the topography payload will be reminded in the first section of this paper. SRAL MAIN FUNCTIONS SRAL is a nadir-looking radar operating in dual frequency (Ku-band used as main frequency and Cband used for ionospheric corrections over ocean). The nadir swath allows using the simple deramp technique to perform radar pulse compression