2009alexandercphd.pdf (3.98 MB)
Classification of Full-waveform Airborne Laser Scanning Data and Extraction of Attributes of Vegetation for Topographic Mapping
thesis
posted on 2011-12-07, 12:18 authored by Cicimol AlexanderThere is an increasing demand for urban vegetation mapping, and airborne laser
scanning (ALS) has the unique ability to provide geo-referenced three-dimensional
data useful for mapping of surface features. This thesis examines the ability of
full-waveform and discrete return ALS point data to distinguish urban surface
features, and represent the three-dimensional attributes of vegetation at
different scales in a vector-based GIS environment. Two full-waveform datasets,
at a wavelength of 1550 nm, and a discrete return dataset, at 1064 nm, are used.
Points extracted from the first full-waveform dataset are classified with k-means
clustering and decision tree into vegetation, buildings and roads, based on the
attributes of individual points and the relationships between neighbouring points.
A decision tree is shown to perform significantly better (74.62%) than k-means
clustering (51.59%) based on the overall accuracies. Grass and paved areas could
be distinguished better using intensity from discrete return data than amplitude
from full-waveform data, both values proportional to the strength of the return
signal. The differences in the signatures of surfaces could be related to the
wavelengths of the lasers, and need to be explored further. Calibration of
intensity is currently possible only with full-waveform data. When the decision
tree is applied on the second full-waveform dataset, the backscatter coefficient
proves to be a more useful attribute than amplitude, pointing to the need for
calibration if a classification method using intensity is to be applied on datasets
with different scanning geometries. A vector-based approach for delineating tree
crowns is developed and implemented at three scales. The first scale provides a
good estimation of the tree crown area and structure, suitable for estimating
biomass and canopy gaps. The third scale identifies the number of trees and their
locations and can be used for modelling individual trees.
History
Supervisor(s)
Tansey, KevinDate of award
2010-01-15Awarding institution
University of LeicesterQualification level
- Doctoral
Qualification name
- PhD