Earth, as a single complex system, is changing; these changes affect every aspect of life on the planet and include profound implications on society. Studying the Earth system is essential to understanding the causes and consequences of climate change and other environmental concerns. Space-based observation systems explore interactions among the atmosphere, oceans, land surface interior, ice sheets,biology, and life itself under global coverage and a daily timescale. The present development trend of Earth system study focuses on the important circulation processes（such as energy cycle, water cycle, and biochemical cycle） that drive the Earth system. The water cycle is the most active cycling process and is thus the core foundation of scientific issues in the Earth system. To improve Earth system science and global change research, accurate observations of various spatial-temporal processes and key parameters of the global water cycle should be derived. Moreover, significantly improving the accuracy and synchronization of key water cycle parameter measurements necessitate the development of innovative theory and techniques for observation and retrieval.

the Earth system;energy and water cycle;biochemical cycle;remote sensing observations;water cycle observation mission