Robust Doppler Centroid estimate for ERS and ENVISAT

The algorithm presented is capable of retrieving the correct DC ambiguity and to fit a fine polynomial estimate both on uniform and contrasted scenes. The core of the algorithm exploits a block wise processing: in each block a coarse unambiguous estimate is provided by exploiting both a second order statistic estimator (WDAR) and a higher order technique (MLBF). The final, fine estimate of the unambiguous Doppler is achieved by jointly exploiting the coarse unambiguous estimate with a fine, ambiguous one. The proposed algorithm accounts carefully for large variation of DC with range, like for recent Emergency Backup Mode of ERS and RADARSAT. The final estimate and its confidence is provided by a weighted average of the block measures. Tuning of the weights and additional check ensure robustness. The estimate of the offset frequency constant is then approached and a solution for calibrating its value is provided.