Global observing systems have been playing an increasingly important role in detecting, monitoring and predicting the various changes of the Earth system. In order to acquire various essential observational data of the Earth system, better cross connections and links among the existing operational observing systems are needed, because the global Earth system is composed of many subsystems and is very complex. This paper introduces the developing trend of strengthening the cooperation and liaision among the existed observing systems, and according to In Situ Observations For the Global Observing System——A Compendium of Requirements and Systems, briefly presents the requirements and specifications for in situ observations of global observing systems.