No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
The simulation of GTRF initial realization using GPS data - art. no. 64180K
Abstract
The GTRF initial realization and long-term maintenance follows the state of the art of TRF implementation. In this paper, the background of GTRF realization and the history of ITRF establishment were reviewed firstly. The precious experience gained from IERS activities is very helpful in GTRF realization, based on such situation, so the combined model and strategy for simulating GTRF initial realization by GPS data in the first stage of Galileo project were discussed and. And then 200 GPS Weeks data in SINEX format from three IGS analysis centers COD, ESA and GFZ was used as input data, we apply loose constraint, use the variance factor of weekly time series as apriori weight in the combination, and estimate station coordinate and 7 transformation parameters together. According to this simulation, the translation and scale parameters of three analysis centers are attained by weekly combined solution, while the rotation parameters are just estimated by the data from ESA. With these 7 transformation parameters, the GTRF can be initially realized by alignment to the ITRF by the GSS co-located with ITRF core stations.
ResearchGate has not been able to resolve any citations for this publication.
For the first time in the history of the International Terrestrial Reference Frame, the ITRF2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model. Minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame (TRF). The ITRF2000 origin is defined by the Earth center of mass sensed by satellite laser ranging (SLR) and its scale by SLR and very long baseline interferometry. Its orientation is aligned to the ITRF97 at epoch 1997.0, and its orientation time evolution follows, conventionally, that of the no-net-rotation NNR-NUVEL-1A model. The ITRF2000 orientation and its rate are implemented using a consistent geodetic method, anchored over a selection of ITRF sites of high geodetic quality, ensuring a datum definition at the 1 mm level. This new frame is the most extensive and accurate one ever developed, containing about 800 stations located at about 500 sites, with better distribution over the globe compared to past ITRF versions but still with more site concentration in western Europe and North America. About 50% of station positions are determined to better than 1 cm, and about 100 sites have their velocity estimated to at (or better than) 1 mm/yr level. The ITRF2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the TRF orientation rate. A comparison to relative rotation poles of the NUVEL-1A plate motion model shows vector differences ranging between 0.03° and 0.08°/m.y. (equivalent to approximately 1-7 mm/yr over the Earth's surface). ITRF2000 angular velocities for four plates, relative to the Pacific plate, appear to be faster than those predicted by the NUVEL-1A model. The two most populated plates in terms of space geodetic sites, North America and Eurasia, exhibit a relative Euler rotation pole of about 0.056 (+/-0.005)°/m.y. faster than the pole predicted by NUVEL-1A and located about (10°N, 7°E) more to the northwest, compared to that model.
Recent solutions of the terrestrial reference frame such as ITRF2000 are combined from multi-year data sets that contain station positions at a reference epoch and constant velocities. Analysis of time series of station positions of the geodetic space techniques SLR, GPS, VLBI and DORIS show, however, that these techniques allow to detect variations in station position series with up to a few millimetre accuracy. Therefore, the underlying reference frame needs to assure the same accuracy.In this paper we analyse systematic effects in station position and transformation parameter time series that need to be taken into account for future TRF realisations. These are mainly annual signals that show up as common variations of the global networks as well as local effects on individual stations. These annual signals differ significantly from technique to technique for some co-location sites. Apart from periodic signals the time series show discontinuities (e.g. due to earthquakes or instrumentation changes) and periods of non-linear motion (e.g. post-seismic relaxation). We compute TRF technique solutions of five years of epoch normal equations, which allows to adapt the parameterisation in order to account for the effects mentioned above. The accuracy of the technique-specific solutions is evaluated by comparing the results at co-location sites. For this purpose, we transform the VLBI, SLR and DORIS solutions to the GPS solution by using the measured local ties between GPS and the other techniques.
The Global Positioning System is a constellation of 24–28 satellites, which can be used to define a global terrestrial reference
frame. Daily offsets between a GPS defined frame and ITRF2000 have been estimated using more than a decade of GPS observations
from 1990–2001. A linear fit to the full span of data shows agreement between the two frames at the level of –1ppb and –0.1ppb/year
for scale, 5mm and 0mm/year for the X component of center of mass, –2mm and –3mm/year for the Y component, and 4mm and
6mm/year for the Z component. GPS is a viable tool for defining the global reference frame either alone, or in combination
with other geodetic techniques.