The Geescicnce Laser Altimeter System (GLAS) on the Iee, Cloud and land Elevation Satellite (ICESaO is the first spaceborne lidar instrument for routine global ebservation of the Earth. GLAS records a vertical profile of the returned laser energy from a footprint ef approximate 70m diameter. The GLAS waveform data (GLAOI) and the I.and/Canopy Elevation product (GLA14) provide information on vegetatien spatial structure. In this study the use of the GI.AS data for forest structural parameters

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... rieval was evaluated using airborne LJVIS (NASArs Laser Vegetation Imaging Sensor) data and field measurements. The tree height indices from airborne largefoetprint lidars such as L:VIS haye been successfu11y used fer estimation of forest structural parameters in many studies. The tree height indices, based on lidar return energ}r quartiles from GLAS data were compared te similar tree height indices derived from IJVIS data within the GLAS footprints. The results show that the tree height indices derived from the GLAS and LYIS waveforms were highly correlated. Our analysis shewed that tree height and biomass obtained from field measurements can be predicted from GLAS data. Cornparisons of the near-repeatspass GLAS data acquired in Fall of 2003 (L2A), Fall of 2004 (L3A), and early Summer ef 2005 (L3C) and 2006 (IBF) show that the surtace elevations from GLAS were consistent. When the mean distance between corresponding points from two 4.5km orbits (260 GLAS shots from L2A and L3F) was 82.6rn, the R2 of the elevations from these two orbits was O.997, with a RMSE of 4.lm. The top tree heights from the near-repeat-pass GLAS orbits show signficant differences, prebably due to the heterogeneity of the forests.