Appraisement and Discussion of ITRF2000

Anatomizing the velocity field and definition of ITRF2000,we find that the precise of ITRF2000 frame is better than these of ITRF96 and ITRF97.ITRF96 and ITRF97 are defined through a weighted least squares algorithm with SLR,VLBI and GPS data equally, but ITRF2000 only uses VLBI and SLR data, excluding GPS data. Because GPS technique is deficient in definition of ITRF2000 origin,orientation and scale and rate, the accuracy of ITRF2000 is improved compared with ITRF96 and ITRF97 without using GPS data. However, the linear rates of change of ITRF2000 orientation angles are determined by only 54 sites imposing a geological plate model NNR-NUVEL1A to achieve no net rotation of global frame with respect to the Earth's crust.Analyzing the total angle momentum,we find that ITRF2000 also has net rotation with respect to the Earth's crust. In this paper, a new global plate motion model of ITRF2000VEL is determined based on the ITRF2000 velocity field.In order to achieve no net rotation of ITRF2000 frame, we calculate the total angle momentum | L | of ITRF2000VEL, 0.127°/m·a^-1 to rectify in practice.