Terrestrial laser scanning measurements to characterise temporal changes in forest canopies

Cardozo, FAR

Abstract

Light detection and ranging (lidar) systems are active sensors capable of creating a
permanent three-dimensional (3D) record of forest canopy structure. This 3D
characterisation can provide increased accuracy for aboveground biomass estimates in
high-biomass ecosystems, where passive optical sensors only provide a two-dimensional
(2D) perspective. The aim of this study was to test a quantitative, accurate, and
repeatable method to obtain estimates of canopy biophysical properties and monitor
seasonal variations in forests by using multi-temporal terrestrial laser scanner (TLS) data.
This research is one of the first detailed multi-temporal terrestrial lidar studies undertaken
anywhere in the world. The study site chosen for this research was Delamere Forest,
located in Cheshire, Northwest England. TLS data on vegetation structure were acquired
for seven sampling plots, comprising two broad-leaf and five conifer stands, between
March 2008 and April 2009. Canopy directional gap fractions were derived from the TLS
datasets collected and compared with estimates derived from coincident hemispherical
photographs. The comparison showed that TLS gap fractions estimates were consistently
lower than those estimated from hemispherical photographs. To examine this apparent
difference further the potential information available from the intensity values recorded
by TLS were investigated. The use of this information in the computation of gap fractions
led to a better agreement between estimates derived from both sources, as well as a better
understanding of how intensity values are activated within forest canopies. Estimates of
other biophysical properties were also computed from the TLS data, including leaf area
index, average leaf angle distributions, and clumping index. The analysis of these
estimates highlighted the repeatability and consistency of the TLS measurements in
comparison with corresponding results derived from the hemispherical photographs.
Analysis of the TLS datasets was conducted in order to improve the understanding of the
interaction between lasers and vegetation canopies. The novelty of this research is in
applying a ground-based lidar sensor to characterise the structure of a range of tree
canopies using intensity corrected data, and assessing the utility of estimates of
biophysical properties for monitoring temporal variations in forest canopies.

Citation

Cardozo, F. Terrestrial laser scanning measurements to characterise temporal changes in forest canopies. (Thesis). Salford : University of Salford

• Thesis Type: Thesis
• Deposit Date: Oct 3, 2012
• Award Date: Jan 1, 2011