ITRF97 data analysis

The ITRF97 solution is derived with the following properties :

All the individual matrices were orthogonaly projected using equation (3)
Station positions of the projected solutions were then propagated at their epochs of Minimal Position Variance
The reference frame definition (origin, scale, orientation and time evolution) is achieved in such a way that ITRF97 is in the same system as the ITRF96
Station velocities are constrained to be the same for all points within each site
ITRF97 positions were estimated at epoch 1997.0
Transformation parameters (at epoch 1997.0) and their rates from ITRF97 to each individual solution were also estimated

Combination model

Assuming that for each individual solution s, and each point i, we have position Xⁱ_s at epoch t_s and velocity $\dot X^i_s$ , expressed in a given TRF k.

The combination consists in estimating:

Positions Xⁱ_itrf at a given epoch t₀ and velocities $\dot X^i_{itrf}$ in ITRS
transformation parameters T_k at an epoch t_k and their rates $\dot T_k$ , from the ITRF to each individual frame k