Surface elevation change of the Greenland ice sheet from an analysis of Seasat and Geosat altimeter data

The author calculates the average change in surface elevation from 1978 to 1985 of the Greenland ice sheet using satellite altimeter data processed with the S/V, ESA, and a threshold retracking algorithm. These measurements are then compared with the results obtained by the NASA retracking algorithm. The surface-elevation change was determined using 6272 crossover points computed from the Seasat and Geosat satellites. The results show that all three retracking algorithms produce a significantly smaller growth estimate than the previously reported NASA result. Based upon a comparison of crossover-point standard deviations, this analysis indicates that the growth estimates produced by the S/V, ESA, and threshold retracking algorithms are more accurate than the NASA growth estimate. An analysis of the NASA fits indicates that a mixing of 5 and 9 parameter functional fits on the four waveforms adjacent to a crossover point occurs in over 78% of the dataset. The mixing of the functional fits is shown to reduce the repeatability of the NASA elevations and this results in a larger and less accurate estimate of the growth of the Greenland ice sheet