Integrating terrestrial and airborne lidar to calibrate a 3D canopy model of effective leaf area index

Abstract

Terrestrial laser scanning (TLS) with the Echidna Validation Instrument (EVI) provides an effective and accurate method for calibrating multiple-return airborne laser scanning (ALS) point cloud distributions to map effective leaf area index (LAIe) and foliage profile within a 1-km diameter test site of mature eucalyptus forest at the Tumbarumba research site, New South Wales, Australia. Plot-based TLS foliage profiles are used as training datasets for the derivation of a scaling function applied to calibrate effective leaf area index (LAIe) from a coincident ALS point cloud. The results of this study show that: a) the mean proportion of the total number of returns within 11.3m radius of the TLS scan station was 64%. Increasing the radius decreased the level of detail due to occlusion; b) the relationship between TLS LAIe profile and ALS foliage percentile distribution (PD) using all, primary and secondary returns are not linearly related; and c) regressions between TLS LAIe profile and ALS PD, demonstrate better correspondence using a 5th order polynomial applied to all returns (r2=0.95; SE=0.09m2m−2) than aquasi-physically-based Weibull scaling function. The calibration routine was applied to ALS data within a GIS environment to create a 500m radius 3D map of LAIe. This localised 3D calibration of LAIe was then used as the basis to calculate the overhead canopy extinction coefficient parameter (k), and thereby facilitate upscaling of spatial LAIe estimates to larger domains using a Beer Lambert Law assumption.