Validation of Vegetation Canopy Lidar sub-canopy topography measurements for a dense tropical forest

Abstract

Large footprint (greater than 10 m wide) laser altimetry is a useful technique for mapping topography (including sub-canopy), canopy height and vertical structure in densely vegetated areas. In March 1998, the Laser Vegetation Imaging Sensor (LVIS), an airborne laser altimeter, mapped a ∼800 km 2 area of Costa Rica including the La Selva Biological Station using 25 m-diameter footprints as part of the pre-launch activities of the Vegetation Canopy Lidar (VCL) Mission. To investigate the utility of the lidar technique for making sub-canopy topography measurements, the precision and accuracy of the LVIS elevation measurements from this mission are assessed. Crossover analysis using laser shots whose recorded waveforms contained more than 50% of the total returned energy within their lowest reflections show the elevations have a precision of better than 1 m. Comparison of the LVIS elevations with coincident in situ ground elevation data reveals that the measurements are within ∼1.5 m of each other on less than 3° slopes. All measurements are within ∼5 m of each other (on slopes of up to 30°). These are very encouraging results given that the forests of this region are some of the densest, most complex on Earth, and that mapping their sub-canopy topography are near-impossible using any other remote sensing technique. Given the similarity of the measurement processes of the LVIS and VCL systems, these results suggest that the topographic measurements made by the VCL will meet stated accuracy goals under the majority of measurement conditions.