Three-dimensional forest stand height map production utilizing airborne laser scanning dense point clouds and precise quality evaluation

Abstract

In remote sensing, estimation of the forest stand height is an ever-challenging issue due to the difficulties encountered during the acquisition of data under forest canopies. Stereo optical imaging offers high spatial and spectral resolution; however, the optical correlation is lower in dense forests than in open areas due to an insufficient number of matching points. Therefore, in most cases height information may be missing or faulty. With their long wavelengths of 0.2 to 1.3 m, P-band and L-band synthetic aperture radars are capable of penetrating forest canopies, but their low spatial resolutions restrict the use of single-tree based forest applications. In this study, airborne laser scanning was used as an effective remote sensing technique to produce large-scale maps of forest stand height. This technique produces very high-resolution point clouds and has a high penetration capability that allows for the detection of multiple echoes per laser pulse. A study area with a forest coverage of approximately 60% was selected in Houston, USA, and a three-dimensional color-coded map of forest stands was produced using a normalized digital surface model technique. Rather than being limited to the number of ground control points, the accuracy of the produced map was assessed with a model-to-model approach using terrestrial laser scanning. In the accuracy assessment, the standard deviation was used as the main accuracy indicator in addition to the root mean square error and normalized median absolute deviation. The absolute geo-location accuracy of the generated map was found to be better than 1 cm horizontally and approximately 40 cm in height. Furthermore, the effects of bias and relative standard deviations were determined. The problems encountered during the production of the map, as well as recommended solutions, are also discussed in this paper.