Potential of Angular Velocity Sensing for the gravity field recovery in GRACE-like missions

GRACE-like missions (GRACE, GRACE-FO) are used to map the global time-varying Earth gravity field, which has brought a revolution in geodesy as well as the other subjects of geophysics. Their key payloads are mainly the inter-satellite ranging system: K-Band Ranging system (KBR) for GRACE, KBR and laser ranging interferometer (LRI) for GRACE-FO, of which both measure the distance variations between the twin satellites; the accelerometers to recover the non-gravitational force on the satellites; the satellite attitude measurement components such as star cameras (SCA), Inertial Measurement Unit (IMU) and LRI Fast Steering Mirror (FSM); and GPS receivers for precise orbit determination. Currently, the observation equations used to establish the gravity field recovery are based on observations from inter-satellite range (or range rate) and GPS orbit. However, we will show that the three-dimensional orientation change of the line-of-sight (LOS) connecting both satellites, i.e., the angular velocity vector of the LOS, contains gravity information perpendicular to the LOS. If future missions can measure the angular velocity with sufficient precision, this will increase the resolution of the satellite pair in the East-West direction and decrease the stripe effects in the North-South direction, thus further improving the accuracy of the gravity field solution. We developed observation equations based on the dynamic approach for the angular velocity sensing (AVS) observations and solved them jointly with the observation equations obtained from GPS and KBR/LRI. Our simulation results show that the angular velocity can indeed recover the gravity field in combination with GPS and the results are better than those obtained using only a combination of KBR/LRI and GPS. The optimal results are obtained when the gravity field is solved by combining AVS, KBR/LRI and GPS at the same time. We further analyzed the accuracy requirements of the angular velocity sensing that would allow for improving gravity field solutions in the next generation of gravity missions.