Abstract
High-precision GPS data processing on Bernese has been employed to routinely resolve daily position solutions of GPS stations in the Crustal Movement Observation Network of China (CMONOC). The rank-deficient problems of the normal equation (NEQ) system and the network effect on the frame alignment of NEQs in the processing of CMONOC data on Bernese still present difficulties. In this study, we diagnose the rank-deficient problems of the original NEQ, review the efficiency of the controlled datum removal (CDR) method in filtering out the three frame-origin-related datum contents, investigate the reliabilities of the inherited frame orientation and scale information from the fixation of the GPS satellite orbits and the Earth rotation parameters in establishing the NEQ of the CMONOC network on Bernese, and analyze the impact of the network effect on the position time series of GPS stations. Our results confirm the nonsingularity of the original NEQ and the efficiency of the CDR filtering in resolving the rank-deficient problems; show that the frame origin parameters are weakly defined and should be stripped off, while the frame orientation and scale parameters should be retained due to their insufficient redefinition from the minimal constraint (MC) implementation through inhomogeneous and asymmetrical fiducial networks; and reveal the superiority of a globally distributed fiducial network for frame alignment of the reconstructed NEQs via No-Net-Translation (NNT) MC conditions. Finally, we attribute the two apparent discontinuities in the position time series to the terrestrial reference frame (TRF) conversions of the GPS satellite orbits, and identify it as the orbit TRF effect.
Highlights
In 1998, China Earthquake Administration led the creation of a national scientific project, namely the Crustal Movement Observation Network of China (CMONOC), to monitor crustal deformation in the China mainland and surrounding areas [1,2]
The nonsingularity property of the normal equation (NEQ) disobeys the basic discipline of the minimal constraint (MC) implementation; it yields the estimation of station positions, and generates conspicuous network distortions in the advanced minimally constrained solution
The systematic part of the network distortion reveals that the external additions of the frame origin parameters via NNT MCs interfere with the internal redundant datum contents of the NEQ, and the individual part shows millimeter-level position differences which corrupt the geometrical correlations between GPS stations in the NEQ
Summary
In 1998, China Earthquake Administration led the creation of a national scientific project, namely the Crustal Movement Observation Network of China (CMONOC), to monitor crustal deformation in the China mainland and surrounding areas [1,2]. The EPN center [11] and the Center for Orbit Determination in Europe (CODE) [12] have proposed empirical recommendations for the routine computation of station positions for regional GPS networks (such as the CMONOC network) on Bernese, and the pivotal procedure is to keep all the satellite orbits and the Earth rotation parameters fixed to their “standard” values which are extracted from postprocessing products (such as International GNSS Service (IGS) orbit products) in the final least squares estimation of position parameters. The procedure may introduce external datum contents into the final outcome of the normal equation (NEQ) matrix, which should essentially contain the necessary geometrical correlations among GPS stations and have 3–7 rank deficiencies [13,14]
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