This PhD journey has been an amazing, precious and unforgettable period in my life. My sincerest appreciation to all who have contributed to this thesis and supported me throughout my PhD journey. First and foremost, I would like to express my sincere thanks to my promotor, Prof. Andrew K. Skidmore. Andrew, thank you for your valuable guidance, insightful advice, and continuous support. The discussion we had taught me how to view scientific questions from different perspectives and gradually I became more and more confident when you challenge me. Thanks to your encouragement and trust, I dare to think bigger and explore the topic more freely. I am very grateful for your patient guidance and critical comments during my PhD research. You always remind me the importance of "critical thinking" and "think out of the box", which I will benefit from not only for my PhD research, but also for the rest of my life. Thank you for recommending me to spend a period of my PhD journey in DLR, Germany, which greatly enriched my PhD and life experience.