Closed loop simulation for a magnetic gradiometry mission

While measuring the magnetic field gradient tensor in space is a major technical challenge, the importance of magnetic gradiometry has been recognized already several decades. In the near future the Swarm satellite mission will for the first time measure the East-West gradient of the magnetic field, which contains valuable information on the North-South oriented features of crustal magnetization. In particular, the East- West gradient measurements will resolve much smaller crustal structure than possible by an analysis of the usual field components at the same altitude. Going beyond Swarm, we performed a simulation of a full magnetic gradiometry mission, emphasizing on the benefits of measuring the full gradient tensor in addition to the three field components. Using simulated orbits from a low Earth-orbiting satellite, synthetic data of the magnetic field vector and of the nine elements of the magnetic gradient tensor are calculated using a given (input) magnetic field model, for the various field contributions (in the core, lithosphere, magnetosphere, and ionosphere). We start from the simple case in which only the core and lithospheric field are included and we move on to a more realistic case including the time-varying magnetospheric primary and Earth-induced contribution. At last, also the ionospheric primary and induced field is included, resulting in even more realistic synthetic data. From these synthetic data we estimate field models using either the magnetic vector field measurements only or full gradient observations, and compare our model retrieval with the original (input) model. The results show evidently that the retrieval of the lithospheric field when using gradient observations is significantly better than the retrieval using only vector field data. This study shows qualitatively the scientific benefit of measurements of the gradient tensor in space.