Determination Of Earth Orientation Parameters Research Articles

Impact of Earth Radiation Pressure Physical Analytical Model on Satellite Laser Ranging Orbit Determination

SLR (Satellite Laser Ranging) is a kind of important space geodesy technique for the establishment of a Terrestrial Reference Frame (TRF) and determination of EOP (Earth Orientation Parameters). It determines the origin and scale factor of TRF. The accuracy of future TRF is 1 mm. This requires improving the SLR data processing accuracy and importing higher accuracy SLR satellite data. The Earth Radiation Pressure (ERP) is an important perturbation force for SLR satellites. The traditional Earth radiation pressure model for SLR satellites is the simple Cannon Ball model. This paper establishes the Box-Wing physical Earth radiation pressure model for SLR satellites and takes Lageos-1 as an example to evaluate the physical analytical model. The Lageos-1 is divided into two blocks: metal shell and corner reflectors. The area and optical characteristics of each block are analyzed according to the requirements of three kinds of Earth albedo and emissivity models of point source, experience and grid models. The results show that after importing the physical analytical Earth radiation pressure model, the empirical force acceleration in the T direction is significantly reduced and the orbit overlap arc precision is about 3 mm smaller than that of the original model. The orbit prediction results show that the prediction accuracy of the new Earth radiation pressure model has generally improved significantly. The maximum improvement percentage of the physical analytical model is 12%, 16%, 28% and 25% respectively in the prediction arc length of 1 day, 3 days, 5 days and 7 days. The physical grid model performs the best with the increase of prediction arc length.

Consistency Problems in the Improvement of the IAU Precession–Nutation Theories: Effects of the Dynamical Ellipticity Differences

The complexity of the modeling of the rotational motion of the Earth in space has produced that no single theory has been adopted to describe it in full. Hence, it is customary using at least a theory for precession and another one for nutation. The classic approach proceeds by deriving some of the fundamental parameters from the precession theory, like, e.g., the dynamical ellipticity $$H_{\mathrm{d}}$$ , and then using those values in the nutation theory. The former IAU 1976 precession and IAU 1980 nutation theories followed that scheme. Along with the improvement of the accuracy of the determination of Earth orientation parameters, IAU 1980 was superseded by IAU2000, based on the application of the MHB2000 transfer function to the previous rigid Earth analytical theory REN2000. The latter was derived while the precession model IAU 1976 was still in force, therefore it used the corresponding values for some of the fundamental parameters, as the precession rate, associated to the dynamical ellipticity. The new precession model P03 was adopted as IAU 2006. That change introduced some inconsistency since P03 used different values for some of the fundamental parameters that MHB2000 inherited from REN2000. Besides, the derivation of the basic Earth parameters of MHB2000 itself comprised a fitted variation of the dynamical ellipticity adopted in the background rigid theory. Due to the strict requirements of accuracy of the present and coming times, the magnitude of the inconsistencies originated by this twofold approach is no longer negligible as earlier, hence the need of discussing the effects of considering slightly different values for $$H_\mathrm{d}$$ in precession and nutation theories.

Quantitative analysis of the atmospheric density models applicable for determination of artificial satellite deceleration

For determination of Earth orientation parameters with a satellite laser, ranging their motion should be modeled with the precision of the ranging (3–5 mm). For low Earth orbits (1000 km or lower), the procedure needs atmospheric deceleration force. Precise values of the atmosphere density are the main difficulty there. There are a lot of atmosphere density models for heights to 1500 km. This article deals with NRL-MSISE-00, DTM-2012, and JB2008 empirical atmosphere density models, which are applicable for this task. The quantitative analysis of the models’ precision is given, and some recommendations for their use are formulated.

On radio source selection to define a stable celestial frame

Context. The most accurate realization of a quasi inertial reference frame, the International Celestial Reference Frame (ICRF), is made of 212 defining extragalactic radio sources whose coordinates are determined using VLBI observations. Recent studies demonstrated however that using other sets of sources could improve the frame stability. Aims. This study examines a simple radio source selection scheme to define celestial reference frame axes more stable than the ones as currently defined by the ICRF. Methods. After having derived source coordinate time series from 26 years of VLBI observations, we select the most suitable sources on the basis of their positional variability (rms and slope), and observational history. We determine the axis stability of the frame defined by the selection, as well as its suitability for global geodetic VLBI analyses, i.e., determination of Earth orientation parameters and source and station coordinates. Results. We select four frames made of 196, 200, 262, and 269 sources, respectively, showing a satisfactory sky coverage in both hemispheres. Our selections provide a frame stability improved by up to 40% with respect to the ICRF, and by 20% with respect to the frame as defined by the 247 stable sources of Feissel-Vernier et al. (2006, A&A, 452, 1107). Reanalysis of data with respect to this frame gives astrometric catalogues aligned to the ICRF-Ext.2 within 17 μas. Effects on the Earth orientation parameter estimates and terrestrial reference frame determination remain marginal. Conclusions. In view of the generation of the next ICRF, we recommend that such an algorithm be taken into consideration along with other criteria based on individual characteristics of the radio sources.

The Chinese VLBI network and its astrometric role

AbstractIn this report we present the current status of the Chinese VLBI network (CVN), and the results of satellite tracking experiments in the past few years related to realtime processing of the CVN dataflow and the reliability and precision of the CVN measurements. We briefly outline the prospective astrometric roles of CVN in the studies of long-term monitoring of extragalactic radio sources, densification of radio celestial reference frame, determination of Earth Orientation Parameters and linkage parameters of reference frames as well as the observation of pulsars for deep space autonomous navigation.

Simultaneous determination of Earth orientation parameters and station coordinates from combination of results of different observation techniques

Described is a method for non-regular combination of different techniques, where the normal equations matrix cannot be restored, to obtain a representative set of Earth orientation parameters and station coordinates. The method is based on combining station position vectors transformed to the celestial reference frame, where they are functions of both the EOP and the station coordinates. Three types of constraints are applied to stabilize the system, separate celestial pole offset from polar motion and, to tie the EOP between individual epochs. VLBI, GPS, SLR and Doris data as collected for the ‘IERS SINEX Combination Campaign’ was used to check the method. After combination, dispersion of station coordinates decreased from 0.040 to 0.031 m. The effect of the combination on EOP is of the order of 0.2 mas and it can be seen in Figs. 3 and 4 as a difference of the final and a priori values.

Determination of EOPs with combined SLR data of Lageos 1 and Lageos 2t

In response to an appeal from the International Earth Rotation Service (IERS) and International Laser Ranging Service (ILRS) for the determination of the earth orientation parameters (EOPs), the Center for Astro-Geodynamical Research and Shanghai Astronomical Observatory (SHAO) participated in the analysis and computations of the satellite laser ranging (SLR) data of Lageos 1 and Lageos 2, and submitted the report (SHAG) 2002 L 01 on the EOP (1998–2001) determination with the combined SLR data of Largeos 1 and Lageos 2. To obtain this parameter sequence EOP (SHAG) 2002 L 01, a refined model for the EOP computations was employed. Comparing it with the concurrent EOP (IERS) C 04, the agreement is as good as 0.35 mas for the polar motions X p and Y p , and better than 0.030 ms for the length of day.

Earth Orientation - The Current and Future Situation

Sub-milliarcsecond astrometry often requires an accurate characterization of the orientation of the Earth in a quasi-inertial reference frame. The International Earth Rotation Service (IERS) standards provide the current state of the art in the transformation between celestial and terrestrial reference systems. Improvements in the determination of Earth orientation parameters which describe this transformation continue to be made. Current and future capabilities are given.

A Terrestrial Reference System Consistent with WGRS

AbstractThe IAU and IUGG has jointly established in 1988 an International Earth Rotation Service (IERS) which is in charge of the realization of conventional celestial and terrestrial reference systems, together with the determination of earth orientation parameters which connect them.The theoretical definition of the terrestrial reference system which is realized by IERS through a conventional terrestrial reference frame formed by SLR, LLR, VLBI and GPS stations is presented. In particular its origin, scale, orientation and evolution with time are reviewed, taking into account relativistic and deformation effects.

An Intercomparison of Connected-Element Interferometer and Lunar Laser Earth Rotation Parameters

AbstractThe determination of Earth orientation parameters using techniques which promise an improvement in the precision of their measurements requires a careful evaluation of the systematic errors present in each series of observations. It is now possible to begin to inter-compare two of these sets of observations of the rotation of the Earth (UT1-UTC) obtained routinely and independently. These are the data obtained from laser ranging to the Moon and those derived from the connected-element interferometer information of the U. S. Naval Observatory. Although these data are available for a relatively short time span, it is possible to begin to inter-compare the observations in an effort to derive possible systematic errors existing in the data. This has been done using data from July 1979 to March 1980 in comparison with Bureau International de l’Heure (BIH) data. Using this information, the hypothesis that there is no correlation between the differences of the interferometer and laser ranging data with respect to the BIH must be rejected. This indicates that both sets of observations show that systematic errors do exist in the BIH data. The nature of the correlation of the two series is examined to establish possible models of the systematic errors. A much longer series of data from both techniques is necessary to improve the estimates, and the results will depend critically on adopted models used in the reductions and the degree of smoothing to which the raw data are subjected.