Using existing satellite constellations to complement current and future dedicated gravity field missions

This study explores the feasibility of using satellite constellations to improve the determination of Earth's time variable gravity field. Current dedicated gravity field missions such as GRACE have provided valuable observations of the global gravity field; however, as single satellites (or satellite pair in the case of GRACE), their ground track inherently limits the spatio-temporal resolution they can achieve. As such, GRACE suffers from aliasing effects caused by sub-monthly signals, such as those caused by atmospheric, hydrological and ocean processes, which must be removed by models in the data pre-processing scheme. To improve the observation of the large scale (> 1000 km), high frequency (< 1 month) variations in the gravity field, the concept of using non-dedicated constellations of satellites is investigated. The constellations would consist of an array of GPS-equipped satellites, such as those from commercial satellite communication networks (Iridium NEXT), radio occultation arrays (FORMOSAT-3/COSMIC, CICERO, etc.), or a low-cost array of custom-built micro-satellites. The GPS receivers would provide a high density of observations in the form of derived accelerations which, while much less accurate than those obtained from GRACE, are still sufficient to observe the longest wavelength signals at even sub-daily intervals. Using a series of simulated mission scenarios, a number of potential mission design options for the constellations are evaluated with realistic measurement noise and gravity signal variations. A limited validation of the theoretical predications is also shown using real data processed from the FORMOSAT-3/COSMIC mission. The results support the conclusion that such constellations, acting either independently or when combined with current or future dedicated gravity field missions (e.g., GRACE follow-on), may offer a noticeable improvement in the recovery of the long-wavelength, high-frequency gravity signals.