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

Vegetation canopies represent the interface between the atmosphere and the biosphereand play an important role in determining energy and mass exchange. Accuratecharacterisation of vegetation canopy characteristics is therefore important tounderstand these processes, and remote sensing has been used for the past threedecades to retrieve information on forest structure and canopy variables. Most of thiswork has employed passive optical sensors at a single date to provide two-dimensionalspectral information that may be correlated with a range of variables. In this researchthree-dimensional multi-temporal data was extracted from discrete return airborne laserscanner (ALS) and compared with data from an airborne hyperspectral sensor. The studyaimed to retrieve woodland stand height, LAI and canopy cover from the two sensortypes at Delamere Forest, located in North West England. The data were collectedbetween March 2008 and March 2009 in needle leaved evergreen, needle leaveddeciduous and mixed broad leaved deciduous stands to capture seasonal changes inwoodland structure. Ground data were collected at seven test plots to validate theairborne data, including regular measurements of stand structure using a terrestrial laserscanner (TLS) and upward-looking hemispherical photography. Comparison between theplot-based and TLS-based estimates of tree height and canopy cover showed that the TLScould be used to rapidly and accurately measure tree height, but measurements ofcanopy cover were less reliable. A range of LiDAR metrics were applied to the test plotsacross 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 ofplots, and temporal variations examined. Hyperspectral data were extracted for the sameplots and the LiDAR-derived variables correlated with a range of vegetation indices. Theresults showed moderate relationships between LiDAR and the hyperspectral data.Overall, the research has established that i) TLS and ALS can be used to estimate standheight, but their effectiveness varied with stand characteristics and time ii) ALS can beused to estimate LAI and their estimates also varied with stand characteristics and timeiii) Point based canopy cover estimates from either TLS or ALS are not reliable. Thisresearch has demonstrated the retrieval of forest biophysical variables from three-dimensional LiDAR and two-dimensional hyperspectral imagery in heterogeneous forestcanopies highlighting their potential to capture forest canopy dynamics.

Level dc:type.qualificationlevel

Doctoral (Level 8)

Year dc:date.issued

2012

Author dc:creator

• Janardhan, VB

Language dc:language

en

Identifier

oai:salford-repository.worktribe.com:1337481

OAI identifier oai:identifier

oai:salford-repository.worktribe.com:1337481