| Summary: | This paper presents an assessment of the horizon-tal accuracy and precision of the laser altimetry observations collected by NASA's ICESat-2 mission. We selected the terrain-matching method to determine the position of laser altimeter profiles within a precisely knownn surface, represented by a DEM. We took this classical approach a step further, approx-imated the DEM by planar surfaces and calculated the optimal position of the laser profile by minimizing the square sum of the elevation differences between reference DEMs and ICESat-2 profiles. We found the highly accurate DEMs of the McMurdo Dry Valleys, Antarctica, ideal for this research because of their stable landscape and rugged topography. We computed the 3D shift parameters of 379 different laser altimeter profiles along two reference ground tracks collected within the first two years of the mission. Analyzing these results revealed a total geolocation error (mean + 1 sigma) of 4.93 m for release 3 and 4.66 m for release 4 data. These numbers are the averages of the six beams, expressed as mean + 1 sigma and lie well within the mission requirement of 6.5 m.
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