Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy最新文献

The IGS has been operational for nearly seven years. Recent changes in the data and products archived at the data centers prompts the review of the current IGS data flow and archiving methodologies. This presentation will outline the current structure at the IGS data centers, including the flow of both the daily and hourly data products, and will detail ideas for improvements to the data flow to ensure timely and consistent availability of IGS data and products.

The Receiver Independent Exchange (RINEX) format can be considered as the de facto standard for storing and exchanging GPS and GLONASS data. It is, however, not suited for real-time applications and applications that require a high sample rate, due to its ASCII format. In this paper a new, binary receiver independent exchange format is proposed for both GPS and GLONASS. Software to test the new format is freely available from Delft University of Technology.

Geochemistry of nine Neoproterozoic granitoid bodies in the northwestern margin of the Yangtze Block (YB) has been studied in this paper. Their ages range from 876 Ma to 786 Ma based on U-Pb zircon dating. These granitoids can be divided into three groups in terms of major and trace elements. Rocks of Group I are alkaline series granites characterized by evident negative Eu anomaly (Eu/Eu* = 0.31 to 0.41) with total REE concentrations between 274 to 122 ppm. Group III includes migmatized granites characterized by low REE concentrations (14 to 45 ppm) and positive Eu anomaly (Eu/Eu* = 1.1 to 2.5). Group II comprises tonalite and diorite with REE between the above two groups (ΣREE = 105 to 212 ppm, Eu/Eu* = 0.73 to 0.79). Granitoids of Group II and III belong to calc-alkaline series and I-type, which were formed during the Jinning Orogeny before 820 Ma related to subduction or collision between the Yangtze Block and oceanic Qinghai-Yunnan-Tibet Plate. The Group I granites were formed after 805 Ma in the late stage of or post the Jinning Orogeny. The Neoproterozoic granitoids have ε_Nd(T) values ranging from −4.3 to +4.5 and initial ⁸⁷Sr/⁸⁶Sr ratios ⩽ 0.705, similar to those of the Neoproterozoic granitoids in the other margins of the YB, but different from those of coeval granitoids within the YB which have ε_Nd(T) of −8.1 to −14.2 and initial ⁸⁷Sr/⁸⁶Sr of 0.705 to 0.708. The difference in geochemistry of the three groups was due to difference in their sources. The Neoproterozoic granitoids of this study were formed by magmas probably derived from sources with different proportions of juvenile crust and Meso- to Paleo-Proterozoic crust. The granites of Group III were derived probably from the lower crust. The crust sources for Group I granitoids probably contain less amounts of juvenile crust component and have higher maturity when compared with those for Group II.

The International GPS Service (IGS) has provided GPS orbit products to the scientific community with increased precision and timeliness. Many users interested in geodetic positioning have adopted the IGS precise orbits to achieve cm-level accuracy and ensure long-term reference frame stability. Currently, a differential positioning approach that requires the combination of observations from a minimum of two GPS receivers, with at least one occupying a station with known coordinates is commonly used. The user position can then be estimated relative to one or multiple reference stations using carrier phase observations and a baseline or network estimation approach. Double-differencing observations is a popular way to cancel out common GPS satellite and receiver clock errors. Baseline or network processing is effective in connecting the user position to the coordinates of the reference stations while the precise orbit virtually eliminates the errors introduced by the GPS space segment. This mode of processing has proven to be very effective and has received widespread acceptance. One drawback is that it requires that simultaneous observations be made at reference stations, with the practical constraint that involves. The following details a post-processing approach that uses un-differenced dual-frequency pseudorange and carrier phase observations along with IGS precise orbit products, for stand-alone precise geodetic point positioning (static or kinematic) with cm precision. This is possible if one takes advantage of the satellite clock estimates that are available with the satellite coordinates in the IGS precise orbit products and models systematic effects that cause cm-variations in the satellite to user range. This paper will describe the approach, summarize the adjustment procedure and specify the earth and space based models that must be implemented to achieve cm-level positioning in static mode. Furthermore, station tropospheric zenith path delays with cm-precision and GPS receiver clock estimates precise to 100 picoseconds are also obtained using this approach.

Data from the Turbo-Rogue GPS receiver onboard the Danish Ørsted Satellite are used to derive satellite-to-satellite Total Electron Content (TEC). We present preliminary results obtaining Electronic Density fields from ionospheric tomography using TEC Ørsted data. TEC is based on single frequency measurements, since only the L1 signal is of good quality. The C/A pseudo range (C1) and the L1 phase are used to obtain the TEC measurement. Electron density profiles from individual occultations are derived, based on the Abel transform, and compared with the tomographical solution. The assumption of spherical symmetry in the Abel transform limits the accuracy of the profiles and often results in a bias. We select occultations observed along the orbital plane to minimize the spherical assymetry effects. The tomographic grid is also confined to a narrow torus close to the orbital plane. The TEC calculations are based on data from 6 hour (3.6 orbits) periods. Two days have been selected for this study, December 5, 1999 and February 12, 1999.

Since GPS week 1052, 5 March 2000, the IGS is producing a new combined orbit called the IGS Ultra rapid product, IGU. The combined IGS Ultra rapid products are being made available twice every day, at 3:00 and 15:00 UTC, with a delay of 3 hours after the end of the included data interval, and are based on solutions from up to seven different IGS Analysis Centers. The main reason for the generation of the Ultra rapid products are the requirements, in both timeliness and accuracy, for near-real-time atmospheric monitoring, e.g., weather predictions. Each ultra rapid orbit file covers 48 hours. The first 24 hours of the orbit are based on actual GPS observations (real orbit), the second 24 hours are extrapolated (predicted orbit). Like the IGS Predicted (IGP) orbits, the Ultra rapid orbits are available for real-time usage. However, the quality of the Ultra rapid orbits should be significantly better because the average age of the predictions is reduced from 36 hours (IGP) to 9 hours (IGU). At the 2000 IGS Analysis Center workshop, held at the USNO in Washington, D.C., it was decided that the IGU products were of sufficient quality to replace the IGP products. This change took effect on November 5 with the start of GPS week 1087.

We will demonstrate that the accuracy of the IGS Ultra rapid orbits is at the 30 cm level, in a weighted RMS sense, which is significantly better than the 70 cm accuracy of the IGS Predicted orbits. We will also demonstrate that with this orbit quality it is possible to derive tropospheric zenith path delay estimates with a precision of 7 mm, which corresponds to approximately 1 mm precipitable water vapor. This level of precision is only achieved when “bad” satellite predictions are (automatically) detected and handled.

Analysis of the official EUREF (European reference GPS network) weekly solution series reveals some systematic seasonal errors, especially in the height component. We suspect that the standard fiducial processing strategy causes these errors. In this investigation a non-fiducial strategy has been used to process a subnetwork of 21 EUREF stations for GPS weeks 969–1042: free weekly solutions obtained as Helmert-based combinations of daily solutions followed by Helmert transformation to ITRF97. Bernese, PyGPS and GROSS packages were used. Comparison with the official EUREF solution shows that obtained coordinate time series most likely are free from seasonal errors. The authors consider it important for such a solution to accompany the official one. A comparison of EUREF and VLBI solutions is planned.