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Publié par | Thesee |
Nombre de lectures | 43 |
Langue | English |
Poids de l'ouvrage | 3 Mo |
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N° d'ordre : 4207
THÈSE
PRESENTEE A
L’UNIVERSITÉ BORDEAUX I
ÉCOLE DOCTORALE DES SCIENCES PHYSIQUES ET DE L’INGENIEUR
Par Heather LAWRENCE
POUR OBTENIR LE GRADE DE
DOCTEUR
SPÉCIALITÉ : Électronique
*********************
MODÉLISATION DE L'EFFET DE LA RUGOSITÉ DE SURFACE ET
DE LA LITIÈRE DES COUVERTS NATURELS SUR LES
OBSERVATIONS MICRO-ONDES PASSIVES - APPLICATION AU
SUIVI GLOBAL DE L'HUMIDITÉ DU SOL PAR LA MISSION SMOS
*********************
Soutenue le : 15 décembre 2010
Après avis de :
Mme. Thuy LE TOAN Rapporteur
Mme. Jacqueline BOUTIN Rapporteur
Devant la commission d’examen formée de :
M. Yann KERR Examinateur
M. Francis GROUSSET Examinateur
M. Jean-Pierre LAGOUARDE Examinateur
M. Philippe PAILLOU Examinateur
M. Jean-Pierre WIGNERON Directeur de Thèse
M. François DEMONTOUX Co-Directeur de Thèse
Titre :
Modélisation de l'effet de la rugosité de surface et de la litière des couverts naturels sur les
observations micro-ondes passives : application au suivi global de l'humidité du sol par la
mission SMOS
Résumé :
Dans le cadre de la mission spatiale SMOS (Soil Moisture and Ocean Salinity), nous présentons dans
cette thèse une nouvelle approche numérique de modélisation du calcul de l’émissivité et du
coefficient bi-statique de systèmes forestiers sol-litière en Bande L. Le système sol-litière est
représenté par deux couches diélectriques 3D comportant des interfaces rugueuses, une démarche qui
n’apparait pas actuellement dans la littérature. Nous validons notre approche pour une seule couche en
comparant les simulations de l'émissivité avec celles produites par la méthode des moments et des
données expérimentales. A partir de ce nouveau modèle, nous évaluons la sensibilité de l’émissivité du
système sol-litière en fonction de l’humidité et de la rugosité de la litière. Ce nouveau modèle
permettra de créer une base de données synthétiques d’émissivités calculées en fonction de nombreux
paramètres qui contribuera à améliorer la prise en compte de la litière dans l'algorithme d’inversion
des données de la mission spatiale SMOS.
Mots clés : radiométrie micro ondes des forêts, émissivité des structures sol litière, Modélisation
numérique par éléments finis, rugosité du sol, litière des forêts, HFSS, IEM, SMOSREX, Coefficient
de rétro diffusion, Coefficient bi-statique, mission SMOS
Title:
Modelling the effects of surface roughness and a forest litter layer on passive microwave
observations: application to soil moisture retrieval by the SMOS mission
Abstract:
In the context of the SMOS (Soil Moisture and Ocean Salinity) mission, we present a new numerical
modelling approach for calculating the emissivity and bistatic scattering coefficient of the soil-litter
system found in forests, at L-band. The soil-litter system is modelled as two 3-dimensional dielectric
layers, each with a randomly rough surface, which to our knowledge has not previously been achieved.
We investigate the validity of the approach for a single layer by comparing emissivity simulations
with results of Method of Moments simulations, and experimental data. We then use the approach to
evaluate the sensitivity of the soil-litter system as a function of moisture content and the roughness of
the litter layer. The numerical modelling approach which has been developed will allow us in the
future to create a synthetic database of the emissivity of the soil-litter system as a function of
numerous parameters, which will contribute to validating and improving the inversion algorithm used
by the SMOS mission to retrieve soil moisture over forests.
Key Words: microwave forest radiometry, soil-litter emissivity, FEM numerical modelling, soil
roughness, forest litter, HFSS, IEM, SMOSREX, backscattering coefficient, bistatic scattering
coefficient, SMOS mission
Acknowledgements
The work of this thesis was made possible by the joint financial support of the Aquitaine Region and
the Centre Nationale d’Etudes Spatiales (CNES), to whom go my grateful thanks. Many people also
supported me directly during my PhD, particularly in the IMS and INRA-EPHYSE laboratories in
Bordeaux. I would like to thank in particular the following people:
- François DEMONTOUX for all his help and support as my PhD co-director, always willing to
give me time and help when required, and to send emails and make phone calls on my behalf.
I also remember especially the occasional practical joke, the wide-ranging discussions over
coffee (or tea) breaks, and the banter when France were playing England, all of which
provided a relaxed working environment
- Jean-Pierre WIGNERON, my PhD director, for always making time to see me when I needed
help, for his constantly invaluable input and advice, and teaching, for his sense of humour and
for his kindness and support during the occasional stresses of the last three years.
- The SMOS team led by Yann KERR in CESBIO laboratory, Toulouse, for making this work
possible under the SMOS umbrella. I would like to thank in particular Arnaud MIALON for
his help in providing and explaining data and his collaboration on the SMOSREX 2009 soil-
litter experimental campaign
- Philippe PAILLOU for the very helpful discussions around numerical modelling and radar
scattering, and for his advice and input in planning the work at the early stages
My thanks go also to Liang Chen and T.D. Wu, for answering my questions by email and providing
me with the AIEM model, to Marc Crapeau for kindly talking me through matlab programming one
Friday afternoon, and to Alain Kruszewski for driving me the 2 hours to the SMOSREX site and back
in the cold and sometimes rainy winter and for his help on the SMOSREX 2009 campaign. I would
like to thank all members of INRA-EPHYSE and IMS-MCM laboratories for their support and
camaraderie over the years, and would particularly like to thank the INRA “non-permanents” for the
wonderful lab community they provided.
Many thanks also to my two thesis reviewers Jacqueline BOUTIN, and Thuy LE TOAN, for
evaluating my work, for putting up with the short time limit we had to give and for all their helpful
suggestions and corrections, and also to all members of the jury for their insightful comments and
helpful discussion during the viva and afterwards.
Lastly, to all my friends and family, near or far, thank you for your love and support, in particular to:
Guilherme Bontorin, Priscilla Boyer, Jérémie Brusimi, Faith Gischler, Luc Gischler, Jennifer Grant,
Marie Guillot, Mena Hatchman, Stephanie Hayes, Emilie Hobday, Julien Lahoudere, Amanda
Lawrence, Carol Lawrence, Hazel Lawrence, Peter Lawrence, Virginie Moreaux, Damien Parent,
Tovo Rabemanantsoa, Jean-Charles Samalans, Sylvain Schnee, Alex Soudant, Katharina Spannraft,
Kat Vyce, and Nathalie Yauschew-Raguenes, to name but a few of those who have greatly enriched
this 3-year journey.
For my Father Contents
1. Introduction ................................................................................................................................... 2
2. Background Theory ...................................................................................................................... 6
2.1 Passive and Active Remote Sensing ........................................................................................ 6
2.2 Electromagnetism .................................................................................................................... 6
2.2.1 Maxwell’s Equations ....................................................................................................... 7
2.2.2 The Wave Equation ......................................................................................................... 9
2.2.3 Plane Waves and Polarisation ....................................................................................... 10
2.2.4 A Superposition of Waves ............................................................................................. 11
2.2.5 The Poynting Vector...................................................................................................... 13
2.2.6 Waves at boundaries ...................................................................................................... 13
2.2.6.1 Reflection and Transmission coefficients for H and V polarization ......................... 14
2.2.6.2 Total Reflection and the Brewster Angle ................................................