Erhu Wei

Mars Cruise Orbit Determination from Combined Optical Celestial Techniques and X-ray Pulsars

Jiandong Liu1,2, Erhu Wei3 and Shuanggen Jin1,4 1(Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China) 2(University of Chinese Academy of Sciences, Beijing 100049, China) 3(School of Geodesy and Geomatics, Wuhan University, Wuhan 430079, China) 4(Department of Geomatics Engineering, Bulent Ecevity University, Zonguldak 67100, Turkey) (E-mail: ehwei@sgg.whu.edu.cn)

High frequency variations of Earth Rotation Parameters from GPS and GLONASS observations.

The Earths rotation undergoes changes with the influence of geophysical factors, such as Earths surface fluid mass redistribution of the atmosphere, ocean and hydrology. However, variations of Earth Rotation Parameters (ERP) are still not well understood, particularly the short-period variations (e.g., diurnal and semi-diurnal variations) and their causes. In this paper, the hourly time series of Earth Rotation Parameters are estimated using Global Positioning System (GPS), Global Navigation Satellite System (GLONASS), and combining GPS and GLONASS data collected from nearly 80 sites from 1 November 2012 to 10 April 2014. These new observations with combining different satellite systems can help to decorrelate orbit biases and ERP, which improve estimation of ERP. The high frequency variations of ERP are analyzed using a de-trending method. The maximum of total diurnal and semidiurnal variations are within one milli-arcseconds (mas) in Polar Motion (PM) and 0.5 milli-seconds (ms) in UT1-UTC. The semidiurnal and diurnal variations are mainly related to the ocean tides. Furthermore, the impacts of satellite orbit and time interval used to determinate ERP on the amplitudes of tidal terms are analyzed. We obtain some small terms that are not described in the ocean tide model of the IERS Conventions 2010, which may be caused by the strategies and models we used or the signal noises as well as artifacts. In addition, there are also small differences on the amplitudes between our results and IERS convention. This might be a result of other geophysical excitations, such as the high-frequency variations in atmospheric angular momentum (AAM) and hydrological angular momentum (HAM), which needs more detailed analysis with more geophysical data in the future.

Earth Rotation Parameter Estimation from GNSS and Its Impact on Aircraft Orbit Determination

Earth rotation parameters (ERP) play a key role in connecting the International Celestial Reference Frame (ICRF) and the International Terrestrial Reference Frame (ITRF). Furthermore, high precision orbit determination and positioning need the precise ERPs, while ERPs are closely related the geophysical fliud mass redistribution and geodynamics. In this paper, global uniformly distributed 75 IGS stations with more than 60 sites tracking GPS+GLONASS simultaneously are selected to estimate Earth Rotation Parameters. Accuracy and method to improve ERP from only IGS stations in and neighboring China are also analyzed in order to provide the reference for BeiDou ERP estimation. The results show that the precision of Polar motion (PM) estimated from daily GPS and GLONASS observations can be achieve at the precision of 0.066 and 0.157 mas, respectively and the precision of length of day (LOD) can achieve at 0.0283 and 0.0289 ms when compared to IERS C04 solutions, respectively. The precision of PM and LOD from regional stations with daily GPS (GLONASS) observations are better than 0.178 mas (0.365 mas) and 0.0291 ms (0.0360 ms), respectively. The precision of PM and LOD from combined GPS+GLONASS are better than 0.153 mas and 0.0292 ms. In addition, the impact of ERP error on aircraft orbit is furthermore discussed. The impact on the LOD is greater than the PM. The orbital error can respectively reach 1, 1 and 0.1 m in X, Y and Z direction with 0.5 mas error in PM and 0.5 ms error in LOD.

Design of Geodetic SVLBI Satellite Orbit and Its Tracking Network

SVLBI (space very long baseline interferometry) has some important potential applications in geodesy and geodynamics, for which one of the most difficult tasks is to precisely determine the orbit of an SVLBI satellite. This work studies several technologies that will possibly be able to determine the orbit of a space VLBI satellite. Then, according to the types and characteristics of the satellite and the requirements for geodetic study and the geometry of the GNSS (GPS, GALILEO) satellite to track the space VLBI satellite, the six Keplerian elements of the SVLBI satellite (TEST-SVLBI) are determined. A program is designed to analyze the coverage area of space of different altitudes by the stations of the network, with which the tracking network of TEST-SVLBI is designed. The efficiency of tracking TEST-SVLBI by the network is studied, and the results are presented.

INS-Aided Single-Frequency Cycle-Slip Detection for Real-Time Kinematic GNSS

GNSS ambiguity fixed solution can greatly improve the accuracy of GNSS/INS integrated system. But it is difficult to achieve perfect real-time dynamic single frequency cycle-slip detection merely by GNSS observations especially in complex environment. Inertial assisted cycle-slip detection terms (DTs) based on station-satellite double-differences and satellite single-difference observations are derived. The error characteristic of the DT is analyzed emphatically. The DT error is affected by the drift of INS error. In addition, the magnitude of the influence on different satellites is related to the angle between its station-satellite vector and that that vector of the reference satellite. Thus, it is important to select reference satellite. It is proposed that two group of DTs can be used together by selecting two different reference satellites. The threshold of detection is estimated in a sliding window, where the DTs, whose INS error is submerged in GNSS error, are removed in order to reflect INS error. The method of threshold estimating has stronger self-adaptability.

Calculating High Frequency Earth Rotation Parameters Using GPS Observations and Precision Analysis

The earth rotation parameters (ERP) have a strong correlation with the migration and movement of earth materials, extraterrestrial world gravity and the load deformation of solid earth. On the other hand, ERP is a very important parameter when converting the earth reference system to the celestial reference system. But the International Earth Rotation Service(IERS) and International GNSS Service(IGS) only release one ERP per day which cannot satisfy the user who need the high frequency of ERP. However, there are amounts of Global Positioning System(GPS) data which can be used to estimate ERP with high time resolution and long time span. Based on this, global uniformly distributed 40 IGS stations are selected to estimate ERP by using the data of the Day of Year(DOY) from 1 to 180 of 2015 with Bernese soft 5.0. In the first part, 24 h resolution of ERP is estimated. The precision of polar motion \( x_{p} \), \( y_{p} \) can be achieved at the precision 0.289, 0.245 mas while the precision of UT1-UTC can be achieved at 0.0342 ms which are made a difference with the results of IGS. In the last part of the paper, the 2 h resolution of ERP are estimated and high frequency time series are got. The precision of high frequency polar motion \( x_{p} \), \( y_{p} \) can be achieved at the precision 0.754, 0.688 mas and the precision of high frequency UT1-UTC can be achieved at 0.1050 ms which are made a difference with the results of IGS at UTC 12:00. The high frequency results have lower precision and stability compared with 24 h resolution results, but still in the acceptable range. Both the results of 24 h resolution and high frequency series have different degrees of systematic deviation. The research above can provide a reference for calculating ERP using BeiDou observations.

On the periods of polar motion with VLBI observations

In this paper, the polar motion series is obtained by processing the 09–10 VLBI data downloaded from IVS. The precision of the polar motion series is also been estimated. In order to extracting the periodical components of the polar motion series, the spectrum analysis method of FFT is applied to the polar motion series after interpolating and wavelet de-noising.

On the earth rotation with GPS and VLBI observations

In this paper, first of all, VLBI observations (NGS format) are used to estimate the earth rotation parameters (ERP). Secondly, the NGS data related GPS observations by the GPS stations co-located with the above VLBI stations are used to estimate the ERP. Thirdly, their results are respectively compared with IERS 08 C04, which shows that the result of GPS cannot get the precision of VLBI stations of equal number. So, 22 GPS stations distributed evenly are chosen to estimate the ERP, the result of which shows that the precision of ERP estimated by GPS has not only been improved a lot, but also it can almost achieve precision of ERP estimated by the VLBI when the number of GPS stations is added to 80.

On the correlation between changes in LOD and earth-moon distance with VLBI observations

In this paper, Changes in length of day (ΔLOD) are obtained through the processing of the 2009.1–2010.11 VLBI data; the time series of distance of the Moon and Earth obtained from Jet Propulsion Laboratory (JPL) ephemeris are calculated. Trend of Δ LOD and the Earth-to-Moon distance are removed, and the periods of them are calculated with spectral analysis. The correction between the Earth-to-Moon distance and the periodical components of ΔLOD extracted by wavelet analysis is analyzed.

On the influence of pole tide to VLBI baselines

In this paper the current pole tide model has been presented. The lengths of the VLBI baselines have been estimated with CONT08 VLBI data sets. And the influence of pole tide on the determination of VLBI baseline has been analyzed.