A robust threshold retracking algorithm for extracting ice-sheet surface elevations from satellite radar altimeters

A threshold retracking algorithm for processing ice-sheet altimeter data is presented. The author performed extensive comparisons between the threshold algorithm and three other ice-sheet retracking algorithms. The algorithm comparisons were made using Seasat and Geosat datasets comprised of over 30,000 crossover points. The author's results show that the threshold retracking algorithm produces ice-sheet surface elevations that are more repeatable than the elevations derived from all the other retracking algorithms. For analysis of long-term change in ice-sheet surface elevations, it is critical that a retracking algorithm produce repeatable elevations. The more consistent an algorithm is in selecting the retracking point the less likely that biases will be introduced by the retracking scheme in the elevation change measurement. For this reason, the robust threshold retracking algorithm has been adopted by NASA/GSFC as an alternative to their existing algorithm for production of ice-sheet altimeter datasets under the NASA Pathfinder program. The threshold algorithm will be used to re-process existing ice-sheet altimeter datasets and to process the datasets from future altimeter missions.