Comparison of Small-footprint and Large-footprint Waveform Lidar for Terrestrial Surface Characterization

Abstract

Small-footprint airborne lidar (Light Detection and Ranging) topographic mapping is widely used in the commercial and research sectors for applications including shoreline monitoring, forestry, flood zone delineation, and urban mapping. A new module developed by Optech, Inc. to digitally record the entire returned lidar pulse has been integrated into, and runs simultaneously with, a conventional small-footprint lidar system operated by the University of Texas (1). Small-footprint airborne waveform lidar data was flown over Freeman Ranch located in Central Texas on August 12, 2005. The objectives for the Freeman Ranch lidar project include 1) the comparison of waveform ranging to the standard discrete return Airborne Laser Terrain Mapping (ALTM) product and 2) the comparison of small-footprint waveform lidar to large-footprint waveform lidar from the Geoscience Laser Altimeter System (GLAS) onboard ICESat. The preliminary analysis of small-footprint waveforms indicates an overall improvement in canopy penetration and subsequent detection of underlying topography compared with the discrete ALTM last return. For the Freeman Ranch site, the small-footprint waveform data were synthesized to simulate a GLAS waveform using the same energy power distribution function as GLAS. Results indicate that synthesized waveforms were a good qualitative fit to the returned GLAS waveforms. However, preliminary analysis indicates an increase of error in the GLAS elevation with increasing amounts of woody cover within the footprint.