Integrated scientific and societal user requirements and functional specifications for the GGOS

As discussed in the previous chapters, the terrestrial reference frame is the foundation for virtually all space-based and ground-based Earth observations. Through its tie to the celestial reference frame by the time-dependent Earth rotation parameters it is also fundamentally important for interplanetary spacecraft tracking and navigation. Providing an accurate, stable, homogeneous, and maintainable terrestrial reference frame, celestial reference frame, and the Earth rotation parameters linking them together is one of the essential goals of GGOS. In recent decades, the geodetic techniques also contribute to the database of Earth observations in particular related to mass transport, dynamics, and ionosphere and troposphere parameters. Observations of changes in the Earth’s geometry (solid Earth surface, sea surface, lake surfaces, and ice surfaces) are an important contribution to the Earth observation database serving a wide range of applications. In this chapter, the requirements of the diverse set of scientific and societal users concerning the terrestrial and celestial reference frames, the associated Earth rotation parameters, and the complementary gravity measurements are first summarized. Subsequently, the requirements in terms of a number of quantities observed by geodetic techniques or determined in geodetic analysis are compiled. The tasks, products, and specifications of the GGOS that are needed in order to meet the most demanding requirements of the users are then presented.