If You Climb Up A Tree, You Must Climb Down The Same Tree. But How High Was It?
Abstract Vegetation structure, the horizontal and vertical distributions of plant biomass, varies in response to environmental and historical factors as well as species composition. A quantitative understanding of the spatial variability of structure is important for a number of mapping and modelling tasks, including biodiversity assessment, biomass measurement, fire and fuel modelling and to parameterise wind and water erosion models. There are several operational programs to map the extent of woody vegetation across Australia, and these are often employed in conjunction with broad floristic formations, subformations and associations to inform estimates of growth form, cover and vertical structure. There are also many regions where Lidar data have been acquired to produce highly accurate vegetation structure maps, but due to the cost and processing overhead these data are discontinuous across the landscape.
Abstract This research reports the results of aggregating full waveform space-borne Lidar within mapped vegetation associations to retrieve vertical structure information continuously across the landscape at potentially a national scale. Freely available Ice, Cloud and land Elevation Satellite/Geoscience Laser Altimeter System (ICESat/GLAS) data has provided in excess of 10,000,000 return waveforms across Australia over its six year lifetime. Once adjusted for the different laser period intensities and footprints, these waveforms were aggregated within regional ecosystem polygons to produce an integrated return waveform for each ecosystem that was used to derive mean canopy and understorey height, depth and density. Due to the large number of returns, these retrievals are near continuous across the landscape at the scale of regional ecosystems, enabling them to be used for inventory and modelling applications. Comparison with airborne Lidar over several test sites show excellent agreement and work is underway to extend the analysis to assess change in vegetation structure over the six years of ICESat data.
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