What is the accuracy of GLAS elevation measurements?

Surface roughness greatly affects the elevation measurement accuracy. Over most of the ice sheets, the accuracy of each elevation measurement is 15 cm. Average ice elevation changes less than 1 cm will be detected by averaging the elevation differences observed at many points in selected regions of the ice sheets. Over land, the vertical accuracy of the elevation measurements will be better than a meter in regions of low slope and up to 10 m in regions of large slopes.

Areas of high roughness and/or slope produce a broadening (or even multiple peaks) in the returned energy (y) vs. time (x) waveform from a single laser pulse. This broadening has the effect of increasing the uncertainty in assigning a single average elevation to the area within the GLAS footprint without independent estimates of both the slope and roughness.