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L'utilisation de la polarimétrie radar et de la décomposition de Touzi pour la caractérisation et la classification des physionomies végétales des milieux humides; le cas du Lac Saint-Pierre
| Content Provider | Semantic Scholar |
|---|---|
| Author | Gosselin, Gabriel |
| Copyright Year | 2013 |
| Abstract | Les milieux humides remplissent plusieurs fonctions ecologiques d’importance et contribuent a la biodiversite de la faune et de la flore. Meme s’il existe une reconnaissance croissante sur l’importante de proteger ces milieux, il n’en demeure pas moins que leur integrite est encore menacee par la pression des activites humaines. L’inventaire et le suivi systematique des milieux humides constituent une necessite et la teledetection est le seul moyen realiste d’atteindre ce but. L’objectif de cette these consiste a contribuer et a ameliorer la caracterisation des milieux humides en utilisant des donnees satellites acquises par des radars polarimetriques en bande L (ALOS-PALSAR) et C (RADARSAT-2). Cette these se fonde sur deux hypotheses (chap. 1). La premiere hypothese stipule que les classes de physionomies vegetales, basees sur la structure des vegetaux, sont plus appropriees que les classes d’especes vegetales, car mieux adaptees au contenu informationnel des images radar polarimetriques. La seconde hypothese stipule que les algorithmes de decompositions polarimetriques permettent une extraction optimale de l’information polarimetrique comparativement a une approche multipolarisee basee sur les canaux de polarisation HH, HV et VV (chap. 3). En particulier, l’apport de la decomposition incoherente de Touzi pour l’inventaire et le suivi de milieux humides est examine en detail. Cette decomposition permet de caracteriser le type de diffusion, la phase, l’orientation, la symetrie, le degre de polarisation et la puissance retrodiffusee d’une cible a l’aide d’une serie de parametres extraits d’une analyse des vecteurs et des valeurs propres de la matrice de coherence. La region du lac Saint-Pierre a ete selectionnee comme site d’etude etant donne la grande diversite de ses milieux humides qui y couvrent plus de 20 000 ha. L’un des defis poses par cette these consiste au fait qu’il n’existe pas de systeme standard enumerant l’ensemble possible des classes physionomiques ni d’indications precises quant a leurs caracteristiques et dimensions. Une grande attention a donc ete portee a la creation de ces classes par recoupement de sources de donnees diverses et plus de 50 especes vegetales ont ete regroupees en 9 classes physionomiques (chap. 7, 8 et 9). Plusieurs analyses sont proposees pour valider les hypotheses de cette these (chap. 9). Des analyses de sensibilite par diffusiogramme sont utilisees pour etudier les caracteristiques et la dispersion des physionomies vegetales dans differents espaces constitues de parametres polarimetriques ou canaux de polarisation (chap. 10 et 12). Des series temporelles d’images RADARSAT-2 sont utilisees pour approfondir la comprehension de l’evolution saisonniere des physionomies vegetales (chap. 12). L’algorithme de la divergence transformee est utilise pour quantifier la separabilite entre les classes physionomiques et pour identifier le ou les parametres ayant le plus contribue(s) a leur separabilite (chap. 11 et 13). Des classifications sont aussi proposees et les resultats compares a une carte existante des milieux humides du lac Saint-Pierre (14).Finalement, une analyse du potentiel des parametres polarimetrique en bande C et L est proposee pour le suivi de l’hydrologie des tourbieres (chap. 15 et 16). Les analyses de sensibilite montrent que les parametres de la 1re composante, relatifs a la portion dominante (polarisee) du signal, sont suffisants pour une caracterisation generale des physionomies vegetales. Les parametres des 2e et 3e composantes sont cependant necessaires pour obtenir de meilleures separabilites entre les classes (chap. 11 et 13) et une meilleure discrimination entre milieux humides et milieux secs (chap. 14). Cette these montre qu’il est preferable de considerer individuellement les parametres des 1re, 2e et 3e composantes plutot que leur somme ponderee par leurs valeurs propres respectives (chap. 10 et 12). Cette these examine egalement la complementarite entre les parametres de structure et ceux relatifs a la puissance retrodiffusee, souvent ignoree et normalisee par la plupart des decompositions polarimetriques. Wetlands fill many important ecological functions and contribute to the biodiversity of fauna and flora. Although there is a growing recognition of the importance to protect these areas, it remains that their integrity is still threatened by the pressure of human activities. The inventory and the systematic monitoring of wetlands are a necessity and remote sensing is the only realistic way to achieve this goal. The primary objective of this thesis is to contribute and improve the wetland characterization using satellite polarimetric data acquired in L (ALOSPALSAR) and C (RADARSAT-2) band. This thesis is based on two hypotheses (Ch. 1). The first hypothesis stipulate that classes of plant physiognomies, based on plant structure, are more appropriate than classes of plant species because they are best adapted to the information content of polarimetric radar data. The second hypothesis states that polarimetric decomposition algorithms allow an optimal extraction of polarimetric information compared to a multi-polarized approach based on the HH, HV and VV channels (Ch. 3). In particular, the contribution of the incoherent Touzi decomposition for the inventory and monitoring of wetlands is examined in detail. This decomposition allows the characterization of the scattering type, its phase, orientation, symmetry, degree of polarization and the backscattered power of a target with a series of parameters extracted from an analysis of the coherency matrix eigenvectors and eigenvalues.The lake Saint-Pierre region was chosen as the study site because of the great diversity of its wetlands that are covering more than 20 000 ha. One of the challenges posed by this thesis is that there is neither a standard system enumerating all the possible physiognomic classes nor an accurate description of their characteristics and dimensions. Special attention was given to the creation of these classes by combining several data sources and more than 50 plant species were grouped into nine physiognomic classes (Ch. 7, 8 and 9). Several analyzes are proposed to validate the hypotheses of this thesis (Ch. 9). Sensitivity analysis using scatter plots are performs to study the characteristics and dispersion of plant physiognomic classes in various features space consisting of polarimetric parameters or polarization channels (Ch. 10 and 12). Time series of made of RADARSAT-2 images are used to deepen the understanding of the seasonal evolution of plant physiognomies (Ch. 12). The transformed divergence algorithm is used to quantify the separability between physiognomic classes and to identify the parameters (s) that contribute the most to their separability (Ch. 11 and 13). Classifications are also proposed and the results compared to an existing map of the lake Saint-Pierre wetlands (Ch.14). Finally, an analysis of the potential of polarimetric parameters in C and L-band is proposed for the monitoring of peatlands hydrology (Ch. 15 and 16). Sensitivity analyses show that the parameters of the 1st component, relative to the dominant (polarized) part of the signal, are sufficient for a general characterization of plant physiognomies. The parameters of the second and third components are, however, needed for better class separability (Ch. 11 and 13) and a better discrimination between wetlands and uplands (Ch. 14). This thesis shows that it is preferable to consider individually the parameters of the 1st, 2nd and 3rd components rather than their weighted sum by their respective eigenvalues (Ch. 10 and 12). This thesis also examines the complementarity between the structural parameters and those related to the backscattered power, often ignored and normalized by most polarimetric decomposition. The temporal (seasonal) dimension is essential for the characterization and classification of plant physiognomies (Ch. 12, 13 and 14). Images acquired in spring (April and May) are needed to discriminate between upland and wetlands while images acquired in summer (July and August) are needed to refine the classifications of plant physiognomies. A hierarchical classification tree developed in this thesis represents a synthesis of the acquired knowledge (Chapter 14). Using a relatively small number of polarimetric parameters and simple decision rules, it is possible to identify, among other, three low marshes classes and to discriminate with success herbaceous high marshes from other physiognomic classes without using ancillary data source. The results obtained are comparable to those from a supervised classification using two Landsat-5 images with an overall accuracy of 77.3% and 79.0% respectively. Various classifications using the support vector machine (SVM) can reproduce the results obtained with the hierarchical classification tree. But the possible exploitation by the SVM of a higher dimensionality, with a maximum overall accuracy of 79.1%, does not allow however to achieve significantly better results. Finally, the phase of the Touzi decomposition appears to be the only parameter (in L-band) sensitive to changes in water level beneath the peat surface (Ch. 16). Therefore, this parameter offer a great potential for peatlands hydrology monitoring compared to the HH-VV phase difference. This thesis demonstrates that the Touzi decomposition parameters allow a better characterization, better separability and better classifications of wetlands plant physiognomic classes than HH, HV and VV polarization channels. The grouping of plant species into physiognomic classes is a valid concept. However, some plant species sharing a similar physiognomy, but occupying a different environment (high vs. low marshes), have presented significant differences in their scattering properties. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://papyrus.bib.umontreal.ca/xmlui/bitstream/handle/1866/9867/Gosselin_Gabriel_These_2013.pdf?sequence=2 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
