The primary payload of CryoSat-2 is a radar altimeter with additional capabilities, called SIRAL, for SAR Interferometric Radar Altimeter. This radar is capable of operating in a number of modes, optimised for measurements over different surfaces. A conventional, pulse-width limited (LRM) provides the measurements over the central regions of the ice sheets, to continue the ERS and EnviSat measurement series. The SAR mode enables an enhancement of the spatial resolution along-track, and this mode is used over sea-ice to enable measurements over relatively narrow leads of open water which would be indistinguishable in low-resolution mode. Over the topographic surfaces of the ice-sheet margins this SAR mode is enhanced by interferometric operation using a second antenna (and receiving channel) across-track so that the arrival angle of the echoes may be measured.

The stability of this antenna bench supporting these interferometric antennas is critical to the measurement performance. The orientation of the vector joining the phase centres of the two antennas, i.e. the interferometric baseline, must be known to better than 30 arc-sec in an Earth- fixed reference frame.

For CryoSat-2, transponders are primarily used for the calibration of the datation, range, and interferometric phase. They offer highly accurate measurements of the baseline orientation; due to they have coherent echoes and they are precise located. The corresponding waveforms distinguish themselves from the other ones resulting from natural targets in power and shape.

Objectives

This main objective of this project is to operate the PFAC CDN1 and GVD1 transponders to support monitoring, Cal/Val analysis and comparisons of CryoSat-2 range residuals at transponder locations versus sea-surface calibrations at local tide gauges

Partners:

• isardSAT, Spain (Prime Contractor)
• Technical University of Crete, Greece