The effect of initial values on the determination of ERP by VLBI.
S. Y. Zhu, Ming Zhao · Acta Astronomica Sinica · 1986
The effect of initial value on the determination of ERP by VLBI is twofold. (1) Without good initial (approximate) value means largo correction for the unknowns. If the observation equations are non-linear, the high order terms may not be negligible. This is a commom problem for Least Squares Adjustment. But by taking some measures, one can reduce the number of iteration and save the computer time. (2) To compute τ_c, one needs a priori value for u. In the current software this is available by using BIH provided initial ERP file. Without it, the effect of the rate of ERP may act as an error source, unless the rate of ERP is taken as solved-for parameters. Three measures are suggested in this paper to overcome the above two problems. (1) Extend the formulae to calculate the partial derivatives to reduce the iteration. (2) The rate of ERP be taken as solved-for unknowns. The partial derivatives are given for that purpose. (3) The effect of large correction for ERP be taken into account when one determines the clock error parameters and edits the data.