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Retrieving surface variables by integrating ground measurements and earth observation data in forest canopies : a case study in Speuldersbos forest / Kitsiri Weligepolage (2015)

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Titre :	Retrieving surface variables by integrating ground measurements and earth observation data in forest canopies : a case study in Speuldersbos forest
Type de document :	Thèse/HDR
Auteurs :	Kitsiri Weligepolage, Auteur
Editeur :	Enschede [Pays Bas] : University of Twente
Année de publication :	2015
Collection :	ITC Dissertation num. 269
Importance :	148 p.
Format :	21 x 30 cm
ISBN/ISSN/EAN :	978-90-365-3876-3
Note générale :	bibliographie University of Twente, Faculty of Geo-Information and Earth Observation
Langues :	Anglais (eng)
Descripteur :	[Vedettes matières IGN] Applications photogrammétriques [Termes IGN] aiguille [Termes IGN] albedo [Termes IGN] canopée [Termes IGN] données lidar [Termes IGN] données localisées 3D [Termes IGN] Fagus (genre) [Termes IGN] hauteur des arbres [Termes IGN] image AHS [Termes IGN] image thermique [Termes IGN] modèle numérique de surface de la canopée [Termes IGN] Pinophyta [Termes IGN] Pseudotsuga menziesii [Termes IGN] réflectance végétale [Termes IGN] rugosité [Termes IGN] température au sol
Résumé :	(auteur) The main objective of this study is to integrate tower-based measurements with ED data for estimating spatially and temporally distributed surface variables of a forest canopy for improved quantification of surface-atmosphere interactions. This study mainly focuses on three of the most important surface variables for estimating surface fluxes, namely the aerodynamic roughness, land surface albedo and land surface temperature. In chapter 2, a framework is presented for estimating aerodynamic roughness parameters: the momentum roughness length (z0) and the displacement height (do) of a coniferous forest stand using remote sensing data. The specific objective of the study is to make use of high resolution Terrestrial Laser Scanning (TLS) data together with Airborne Laser Scanning (ALS) data to digitally map the upper canopy surface in order to generate high resolution digital Canopy Height Models (CHMs). The digital CHMs were subsequently used to extract surface geometric parameters of the upper canopy surface. Eventually the surface geometric parameters were used as input variables in the selected morphometric models to estimate aerodynamic roughness parameters. It was observed that the estimated values of zo and do depend very much on the selected model. Comparison of model estimated roughness parameters against the literature values for similar surface types has shown that the technique can be successfully applied to estimate forest surface roughness by tuning some of the model parameters to resemble the forest structure of the study area. Chapter 3 describes the use of these two aerodynamic methods to estimate momentum roughness length and displacement height of Douglas fir forest using simultaneous micrometeorological and flux measurements. When the flux-gradient method was used to objectively determine zo and do, corrections for roughness sub-layer effects proved to be important. A new iterative method is employed to solve the set of equations when the corrections were made. In the absence of experimentally determined roughness sub-layer height, the corrections of Harman and Finnigan (2007) yielded the best overall estimates of aerodynamic parameters. Comparison with results of over 25 other studies has shown that the results obtained in this work fit the general trend rather well. Two quadratic relationships are proposed to predict do and ha based on the observed mean tree height. These simple relationships can be easily incorporated to large scale land surface models, provided that spatially distributed tree height information is available. The flux-variance technique is shown to be robust even when measurements are made in the roughness sub-layer. However the technique cannot be objectively used to estimate zo and do as no explicit method exists to select the exact value for coefficient C1. A detailed investigation of stand level surface albedo variability of a patchwork forest is presented in chapter 4. The top of the canopy reflectance in the visible and near-infrared domain retrieved from airborne and satellite imageries were integrated to estimate spatially distributed surface albedo while the tower-based radiation measurements in the solar-reflective region were used to obtain the temporal variation of surface albedo over a needleleaf forest canopy. The diurnal variation of surface albedo is consistent with the previous findings for needleleaf forest canopies. The spatial mean surface albedo values estimated from remote sensing data for needleleaf (pure Douglas fir), broadleaf (pure Beech) and mixed forest classes are 0.09, 0.13 and 0.11 respectively. Both visual characteristics and descriptive statistics indicate that with increased pixel size, the spatial variability of albedo progressively decreases. The semivariogram analysis was more insightful to perceive the nature and causes of albedo spatial variability in different forest classes in relation to sensor spatial resolution. Finally a theoretical basis for directional LST estimation from top of the atmosphere radiance measurements is presented along with a spatio-temporal analysis of remotely sensed LST and concurrently carried out ground-based radiation together with contact temperature measurements in a Douglas fir forest. For the analysis we used remotely sensed TIR data from Airborne Hyperspectral Scanner to estimate spatially distributed LST of forested area. The AHS sensor, with 10 thermal bands covering the range between 8 and 13pm of the electromagnetic spectrum is an example of the new generation of airborne sensors with multispectral thermal infrared capabilities. The data acquired from the AHS sensors provided the opportunity to retrieve the directional LST of the forest canopy with a very high spatial resolution for both nadir and oblique view angles. Also the concurrent tower-based temperature measurements provided limited ground truth for a spatio-temporal analysis of surface temperature in an area covered with Douglas fir trees. The method adopted here for concurrent determination of LST and LSE is the widely-used TES algorithm together with the MODTRAN4 preprocessor for calculating the required atmospheric contributions. AHS derived average temperature values are generally in good agreement with the tower based component temperature measured at 24 m level whereas the component temperatures (trunk) measured at 17 m are consistently higher. It may be noted that in comparison with off-nadir radiometric temperature the TES method provides average LST with RMSE around 1.9K while the corresponding value with respect to component temperature measured at 24 m is around 1.4 K.
Note de contenu :	1- Introduction 2- Estimation of canopy aerodynamic roughness using morphometric methods 3- Effects of sub-layer corrections on the roughness parametrization of a Douglas fir forest 4- Effects of spatial resolution on estimating surface albedo 5- Retrieving directional temperature using multiplatform thermal data 6- Conclusion and recommendations
Numéro de notice :	14944
Affiliation des auteurs :	non IGN
Thématique :	FORET/IMAGERIE
Nature :	Thèse étrangère
Note de thèse :	PhD : Geo-Information and Earth Observation : University of Twente : 2015
En ligne :	https://research.utwente.nl/en/publications/retrieving-surface-variables-by-inte [...]
Format de la ressource électronique :	URL
Permalink :	https://documentation.ensg.eu/index.php?lvl=notice_display&id=77060

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14944 Retrieving surface variables

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