Observation of the Earth gravity field from space: from the beginnings till future missions based on quantum physics

Different platforms and sensors have been exploited since the start of the space era, with the aim of improving the knowledge of the gravity field of our planet. Then, since the beginning of this century, dedicated missions were designed and launched, providing a wealth of data that have helped estimate more and more accurate gravity field models, improving both spatial and temporal resolution. In recent years, the focus of these missions has been the determination of the temporal variations of gravity field, which are an important source of information for studies of global change phenomena. Thus, gravity field observations from space can give a significant contribution to the determination of many essential climate variables which help explaining phenomena that are changing the world we live in: climate change, distribution of water resources, flooding, melting of ice masses, global sea level rise, etc. In this paper, the basic concepts of gravity field observation from satellite missions will be presented. A short history of satellite missions exploited or specifically designed for the observation of the Earth gravity field will be outlined, coming to the most recent satellite missions and to the planned ones (including the novel concept based on quantum sensors) which will further our insight on several geophysical phenomena. In the final part of the paper,some results will be presented for different mission scenarios analyzed by applyingthe so-called space-wise approach in the frame of recent studies on future satellite gravimetry or gradiometry missions.