基于VLBI资料的ERP高频变化求解方法的研究

Solution of High Frequency Variations of ERP from VLBI Observations

在天测与测地VLBI资料分析软件CALC／SOLVE中,对地球自转参数(ERP) 高频变化的解算采用了附加约束的连续分段线性拟合方法,即要求在两个历元节点之间 ERP变化率小于某事先约定值,并要求ERP在历元节点上连续.实测资料分析表明,当 资料点密度较低时,引入约束条件和要求连续均有助于提高解的稳定性,但也人为降低了 解的客观性,使各历元节点ERP解算结果之间相关.为此,基于CALC／SOLVE的用户 偏导功能,实现了ERP高频变化的直接求解模块,不附加约束,也不要求连续.实测资料 分析表明对ERP高频变化的直接求解模式更为可取.对于长时段VLBI资料的ERP高 频变化求解,需要考虑岁差和章动模型偏差(天极偏移)的影响,编写相应的求解模块, 并成功实现了1979至2003年长时段ERP高频变化求解.比较表明,在考虑了岁差章动 模型偏差的影响时能够显著提高解的精度.为此,在基于VLBI资料解算ERP高频变化 时,建议采用直接求解模式,并考虑岁差章动模型偏差的影响.

In the software CALC/SOLVE of astrometric and geodetic VLBI data analysis, the high frequency variations of the Earth Rotation Parameters (ERP) are determined by a constrained continuous piecewise linear model, that is, the ERP rate within two epoch nodes is constrained to be smaller than a limitation setting, and the ERP is forced to be continuous at epoch nodes. Observation data analysis shows that when the data points are not very dense the constraint and the continuation requirement are helpful to the improvement in the stability of the solution, but degrade the independence of ERP solutions at epoch nodes as well. By using the Userpartial entry of CALC/SOLVE a direct solution module of the high frequency variations of ERP is realized without any constraint on the rate nor the requirement of continuation at nodes. It is shown from real observation reduction that the direct solution mode is feasible. In the solution of high frequency variations of ERP from VLBI observations with long period coverage, the model errors of the precession and nutation (celestial pole offset) should be taken into consideration. A corresponding module is realized and global solutions of the high frequency variation of ERP are successfully performed on the VLBI observations from 1979 to 2003. Comparison of the solutions shows that with the consideration of the pole offsets the precision of parameters could be improved obviously. In the solution of high frequency variation of ERP from VLBI observations, the direct solution mode with the consideration of the pole offsets is accordingly recommended.