Estimation of biophysical properties of woodland canopies using LiDAR and hyperspectral imagery

Janardhan, VB 2012, Estimation of biophysical properties of woodland canopies using LiDAR and hyperspectral imagery , PhD thesis, University of Salford.

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Abstract

Vegetation canopies represent the interface between the atmosphere and the biosphere and play an important role in determining energy and mass exchange. Accurate characterisation of vegetation canopy characteristics is therefore important to understand these processes, and remote sensing has been used for the past three decades to retrieve information on forest structure and canopy variables. Most of this work has employed passive optical sensors at a single date to provide two-dimensional spectral information that may be correlated with a range of variables. In this research three-dimensional multi-temporal data was extracted from discrete return airborne laser scanner (ALS) and compared with data from an airborne hyperspectral sensor. The study aimed to retrieve woodland stand height, LAI and canopy cover from the two sensor types at Delamere Forest, located in North West England. The data were collected between March 2008 and March 2009 in needle leaved evergreen, needle leaved deciduous and mixed broad leaved deciduous stands to capture seasonal changes in woodland structure. Ground data were collected at seven test plots to validate the airborne data, including regular measurements of stand structure using a terrestrial laser scanner (TLS) and upward-looking hemispherical photography. Comparison between the plot-based and TLS-based estimates of tree height and canopy cover showed that the TLS could be used to rapidly and accurately measure tree height, but measurements of canopy cover were less reliable. A range of LiDAR metrics were applied to the test plots across time with strong correlations for height and LAI and weaker correlations for cover. The same metrics were applied to estimate height, cover and LAI at a large number of plots, and temporal variations examined. Hyperspectral data were extracted for the same plots and the LiDAR-derived variables correlated with a range of vegetation indices. The results showed moderate relationships between LiDAR and the hyperspectral data. Overall, the research has established that i) TLS and ALS can be used to estimate stand height, but their effectiveness varied with stand characteristics and time ii) ALS can be used to estimate LAI and their estimates also varied with stand characteristics and time iii) Point based canopy cover estimates from either TLS or ALS are not reliable. This research has demonstrated the retrieval of forest biophysical variables from three-dimensional LiDAR and two-dimensional hyperspectral imagery in heterogeneous forest canopies highlighting their potential to capture forest canopy dynamics.

Item Type: Thesis (PhD)
Contributors: Danson, M (Supervisor), Entwistle, NS (Supervisor) and Gaulton, R (Supervisor)
Schools: Schools > School of Environment and Life Sciences > Ecosystems and Environment Research Centre
Depositing User: Institutional Repository
Date Deposited: 13 Aug 2021 11:41
Last Modified: 27 Aug 2021 21:57
URI: http://usir.salford.ac.uk/id/eprint/61520

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