INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION

CANOPY STRUCTURAL MODELING USING OBJECT-ORIENTED IMAGE

CLASSIFICATION AND LASER SCANNING

First results

Zoltán Vekerdy, Patrick van Laake, Wim Timmermans and Remco Dost

AGRISAR and EAGLE Campaigns Final Workshop

15-16 October 2007

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Objectives

Forest canopy modelling -PAR

Roughness parameters for energy balance modelling

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The experiment

Leica HDS2500 Laser scanner and Leica1200 DGPSSpeulderbos site – pine forest4 scanning elevations between 1 and 30 m above ground level + 4 positions on the ground

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Raw scan data

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Forest and canopy reconstruction (modelling)

Tree models based on geometric bodiesLocation of trees –location of stems (horizontal section, usually at 1.3 m)PAR modelling

…

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Roughness height in energy balance modelling

Aerodynamic roughness height: where wind changes from turbulent to laminarDepends on canopy structureNot directly measurableHigh variability (space and time)Approximated, among others, using LAI, NDVI (indirect canopy structure-related parameters, detectable by RS)

Assumptions: Description of vegetation structure – better understanding of vertical distribution of wind (estimate of drag parameters) / sensible heat flux TLS characterizes the canopy densitySurface elevation model characteristics can be estimated from TLS

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Surface roughness of the forest

Raw Digital Surface Model – 10 cm resolution

Missing pixels nearest neighbourinterpolated – 10 cm resolution

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Variogram analysis of the DSM

Masked out area: only a few missing pixels at the highest resolution –assumption: neglectablemissing details IsotropicResolution dependence…

Variogram surface of 40 cm lag spacing

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Semi-variogram dependence on DSM grid size

Empirical semi-variograms

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Lag distance

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i-var

iogr

am

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Spherical modelSlightly changing range?Exponentially increasing sill

Sill depenance on grid size

y = 474.74x-0.8478

R2 = 0.9972

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Grid size [cm]

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i-var

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am s

ill

SillPower (Sill)

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Vertical section of the forest

At y=473752

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Forest density measure

Where VR = voxel with reflecting surfaceV = voxelf = scaling factor

= ∑∑

VV

fD Rf

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Canopy density distributionCanopy density

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035

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Canopy density

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What is next?

Sensitivity of forest density values to voxel sizeSpatial structure, clusteringResistance against flow at different height according to woody and ‘soft’ (leaf) volumes (scaling factor)Different speciesWind measurements in and above canopy Relation between aerodynamic roughness height and canopy structureRelation between RS parameters and canopy structure (Lidar?)