1. Introduction As an indicator of the degree of surface dryness and wetness, soil moisture (SM) is one of the key parameters in the global water cycle. It plays a critical role in agricultural production, meteorological research, and disaster warning [1]. For the long-term monitoring of SM, the traditional method not only has high equipment cost but also has the problems of complicated operation, waste of manpower and material resources, low efficiency, and limited scope of application [2].
