The invention discloses a GRACE and Swarm time-varying gravity field fusion filtering method based on a
state space model, and the method comprises the steps: taking a spherical
harmonic coefficient as a state quantity, constructing a random walk process equation, introducing three types of observations, employing a quantization parameter for observation
noise and
process noise covariance, constructing according to an order / power law, and carrying out the self-adaptive updating along with the monthly; a Nelder-Mead method is adopted to search for
spectral index parameters, and an EM
algorithm and a statistical method are utilized to update other parameters in a closed / quasi-closed mode; obtaining the state and posterior
covariance of a full
time sequence by using Kalman filtering and RTS
smoothing; in the GRACE and GRACE-FO
window period, continuous reconstruction is carried out by means of a process model and Swarm; and outputting quality evaluation information including monthly gravity field coefficients, posterior
covariance, innovative variance ratio, residual whitening test,
space power spectrum, uncertainty band and the like. According to the method, while physical rationality and calculation feasibility are ensured, a continuous and stable monthly time-varying
gravitational field sequence with quantifiable uncertainty is realized.