Estimating Forest Canopy Structure Using Helicopter-Borne Lidar Measurement

Abstract

LIDAR (Light Detection And Ranging) remote sensing with small-footprint is very useful for ecological studies because three-dimensional canopy structure for evaluating forest functions can be measured. This study aims to compare helicopter-borne LIDAR measurement results with field survey data of individual trees and verify the capability of LIDAR remote sensing to comprehend the stratification of a mixed deciduous forest. A mixed deciduous forest normally has several layers. A procedure using helicopter-borne LIDAR measurement was developed and tested to estimate canopy structure of a mixed deciduous forest with multiple layers. Field survey data, such as tree height, diameter at breast height (dbh), positions of stem bases and tops of trees, and species, were collected for all trees over 5 cm dbh. Helicopter-borne LIDAR measurements were taken with a footprint diameter of 35 cm and a distance between neighboring footprints of 20 cm in summer and winter. We assumed adjoining spaces with 1 m wide along a certain direction in the stand and whole measurement data within each space were projected to a corresponding vertical plane to recover a canopy structure. Scattering points in a vertical plane showed multiple layers of a forest canopy within a corresponding space. A series of projective planes of measurement data for each plot was prepared to verify stratification and identify the top of each tree. The top and second layers could be identified from summer measurements and the shrub layer could be done from winter ones. This analysis indicated that there were several opportunities to use helicopter-borne LIDAR measurement for ecological studies. As a canopy structure of a mixed deciduous forest is particularly complicated, its measurement requires smaller closely-spaced footprints. In addition, two measurement periods, one in summer and one in winter, are effective for obtaining ecological information for a mixed deciduous forest.