International Archives of Photogrammetry and Remote Sensing, Vol. 32, Part 3W14, La Jolla, CA, 9-11 Nov. 1999 
PROGRESS IN LIDAR ALTIMETER REMOTE SENSING OF STAND STRUCTURE 
IN DECIDUOUS AND CONIFEROUS FORESTS USING SLICER DATA. 
Michael A. Lefsky', David J. Harding’, Geoffery G. Parker’ ,Warren B. Cohen , Steven A. Acker 
"Pacific Northwest Experiment Station 
3200 SW Jefferson Way 
Corvallis, OR 97331, USA 
?Laboratory for Terrestrial Physics 
NASA's Goddard Space Flight Center 
Greenbelt MD 20771, USA 
*Smithsonian Environmental Research Center 
P.O. Box 28 
Edgewater, MD 21037, USA 
^Oregon State University, Department of Forest Science 
3200 SW Jefferson Way 
Corvallis, OR 97331, USA 
KEY WORDS: Lidar, forest structure, biomass, canopy. 
ABSTRACT 
Large footprint, waveform sampling lidar altimetry has a number of benefits over traditional, small footprint, single return laser 
altimetry for the remote sensing of forest structure. Nevertheless, its application has been impeded by a lack of 1) algorithms for 
converting the lidar data to biophysical measurements, 2) validation of the resulting measurements, and 3) applications 
demonstrating the utility of the measurements. Over the course of the last five years, we have developed algorithms and software 
packages for the extraction of height, cover, canopy height profile and light transmittance related measurements, and validated them 
using field measurements in two contrasting forested ecosystems: eastern deciduous forests in Maryland and North Carolina, USA; 
and western coniferous Douglas-fir/western hemlock forests at H.J. Andrews Experimental Forest, Oregon, USA. In both systems, 
field measurements of forest height and cover were accurately estimated by the lidar measurements. In eastern deciduous forest, 
SLICER was able to accurately predict canopy height profiles, ie. the vertical distribution of foliage. In addition, estimates of the 
vertical distribution of PAR transmittance derived from the lidar measurements matched field measurements, in terms of the height 
and rate of change in transmittance, in both systems. Interpretative methods to describe canopy structure have ranged from simple 
estimates of the total height and mean height of the canopy, to a complex method describing the entire three-dimensional distribution 
of canopy elements (canopy volume method). These basic measurements of the physical structure of the canopy have been used to 
predict a wide range of forest stand structure attributes, including basal area, aboveground biomass, leaf area index, mean and 
standard deviation of tree diameters at breast height, and density of large individuals. The ability of lidar to predict these variable has 
been very good, as compared with non-lidar remotely sensed estimates, with coefficients of determination usually in excess of 8096 
of variance explained. Through this work, the utility of waveform sampling lidar altimetry has been established, and the 
impediments to its use have been substantially decreased. 
principles of laser altimetry. The capability of traditional laser 
altimeters, that measure a single range to a target, is expanded 
by recording the laser backscatter amplitude with very high 
temporal resolution. The approach yields a measure of the 
height distribution of illuminated surfaces within the laser 
footprint. Recent work has demonstrated that this measure can 
be used to accurately predict both the total biomass (Lefsky, 
1997; Lefsky et al., 1999a; Means et al., 1999; Lefsky 1999b) 
and variability of forest structure (Lefsky, 1999b) over a large 
range of biomass. In this paper, the measurement principles of 
lidar altimeters as applied to canopies and a review of several 
1. INTRODUCTION 
Characterization of canopy structure is a major challenge in 
remote sensing, particularly for moderate to high biomass 
forests. A new class of instruments, referred to here as lidar 
altimeters, developed at NASA's Goddard Flight Space Center 
(Bufton, 1989; Blair et al., 1994; 1997) have demonstrated a 
potential to greatly improve remotely sensed estimates of 
important aspects of canopy structure. These devices measure 
the vertical distribution of canopy structure directly using the