A leading-edge based method for correction of slope-induced errors in ice-sheet heights derived from radar altimetry

Abstract. Satellite radar altimetry has been an important tool for cryospheric applications such as measuring ice-sheet height or assessing snow/ice anomalies (e.g., the extensive melt in Greenland in 2012). Although accurate height measurements are key for such applications, slope-induced errors due to undulating topography within the kilometre-wide pulse-limited footprint can cause multi-meter errors. Therefore different correction methods have been developed ranging from the slope method to the point-based method. Each of these methods have shortcomings as they either neglect the actual topography or the actual footprint that can be estimated by a combination of the leading edge and topography. Therefore, a novel Leading Edge Point-Based (LEPTA) method is presented that corrects for the slope-induced error by including the leading edge information of the radar waveform to determine the impact point. The principle of the method is that only the points on the ground that are within range determined by the begin and end of the leading edge are used to determine the impact point. Benchmarking of the LEPTA method to the slope- and point-based method based on CryoSat-2 LRM acquisitions over Greenland in 2019 shows that heights obtained by LEPTA outperform the other methods when compared to ICESat-2 observations, both in the flat, interior regions of Greenland and in regions with more complex topography. The median difference between the slope-corrected CryoSat-2 and the ICESat-2 heights is almost negligible, whereas the other methods can have a 0.22 m and 0.69 m difference, and the Level-2 data provided by ESA have a 0.01 m difference. The median absolute deviation, which we use as an indicator of the variation of errors, is also the lowest in LEPTA (0.09 m) in comparison to the aforementioned methods (0.22 m and 0.13 m) and ESA Level-2 data (0.15 m). Based on that, we recommend considering LEPTA to obtain accurate height measurements with radar altimetry data, especially in regions with complex topography.