Datation and Range Calibration of Radar Altimeter Exploiting Fully Focused SAR Processing

External calibration of satellite altimeters is commonly used to assess the errors introduced by the instrument when performing its measurements. The on-ground processing of the altimeter acquisitions over an external calibrator is a key step to assess these errors starting from the knowledge of the exact location of the external calibrator and its characteristics. In this letter, a novel on-ground processing is proposed for high pulse repetition frequency altimeters based on the fully focused synthetic-aperture radar (FF-SAR) concept, which relies on the capability of the instrument to preserve the coherency of the transmitted pulses for sufficiently long time. Starting from the FF-SAR processing, methods are here proposed to perform both absolute range calibration and datation calibration. The effectiveness and performance of the proposed approach are verified by processing the transponder acquisitions of CryoSat.