An accurate estimation of the chlorophyll-a (Chla) concentration is crucial for water quality monitoring and is highly desired by various government agencies and environmental groups. However, using satellite observations for Chla estimation remains problematic over coastal waters due to their optical complexity and the critical atmospheric correction. In this study, we coupled an atmospheric and a water optical model for the simultaneous atmospheric correction and retrieval of Chla in the complex waters of the Wadden Sea. This coupled model called MOD2SEA combines simulations from the MODerate resolution atmospheric TRANsmission model (MODTRAN) and the two-stream radiative transfer hydro-optical model 2SeaColor. The accuracy of the coupled MOD2SEA model was validated using a matchup data set of MERIS (MEdium Resolution Imaging SpectRometer) observations and four years of concurrent ground truth measurements (2007)(2008)(2009)(2010) at the NIOZ jetty location in the Dutch part of the Wadden Sea. The results showed that MERIS-derived Chla from MOD2SEA explained the variations of measured Chla with a determination coefficient of R 2 = 0.88 and a RMSE of 3.32 mg·m −3 , which means a significant improvement in comparison with the standard MERIS Case 2 regional (C2R) processor. The proposed coupled model might be used to generate a time series of reliable Chla maps, which is of profound importance for the assessment of causes and consequences of long-term phenological changes of Chla in the turbid Wadden Sea area.

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Writing this thesis was a challenging and fascinating journey for me. There have been many people who have walked alongside me during this journey. I would like to express my sincere appreciation to all these people: First and foremost, I would like to express my special appreciation and thanks to my main supervisor (promotor) Prof.dr.ing Wouter Verhoef, who provided me with the opportunity to do my PhD in his research group at the Faculty of Geo-information Science and Earth Observations (ITC). I consider myself very fortunate to have had the chance to pursue my PhD with him. He has been truly a dedicated mentor and has always showed trust and confidence in me through my research. I could not have maintained interest in my work without his profoundly impressive elegant and clearness of his work, guidance, radiating enthusiasm, endless support, kindness, and unbelievable patience. His open office policy for my questions, being so quick response for my emails, generous in sharing his knowledge, work, and experience are all greatly appreciated.My sincere thanks go to my co-supervisor, Dr.ir. Suhyb Salama, who always supported me during my PhD journey. His friendly advice, constructive comments, notes, and very smart suggestions were always a spark for considering the new ways to improve and rationalize the work. I deeply thank him for all his advice and guidance to help me to rise myself in both of my research and future career.Department of Water Resources (WRS) and providing a comfortable academic environment where I could focus only on my research. I would like to thank the department secretaries, Anke, Tina, and Lindy, for being always so kind, supportive and helpful during my PhD and also Loes Colenbrander for the assistance of my PhD application and the support during my stay at ITC. I am grateful that there was a lovely and supportive Iranian community in Enschede, where I could always found assistance when I needed that, and I thank all of my Iranian friends.My deepest thanks go to my beloved family. Nothing more than their emotional and mental support, presence and sincere belief in my potential could give me the courage of doing what I like to do, and my love and respect for them are beyond the words. I owe all the achievements of my life to my wonderful parents, now and forever, and this thesis is dedicated to them.Last but not least, I would like to especially thank all those people who made me here feel like home with their smiles, kindness, politeness, and understanding. They have given me a feeling of being so lucky to do my PhD in this beautiful country. Thank you, Nederland and Nederlanders! iii Table of Contents Acknowledgments .