This study aims to evaluate and analyze the orbit predictions of selected satellites: geodetic, Global Navigational Satellite Systems (GNSS), and scientific low-orbiting, which are tracked by laser stations. The possibility of conducting satellite laser ranging (SLR) to artificial satellites depends on the access to high-quality predictions of satellite orbits. The predictions provide information to laser stations where to aim the telescope in search of a satellite to get the returns from the retroreflectors installed onboard. If the orbit predictions are very imprecise, SLR stations must spend more time to correct the telescope pointing, and thus the number of collected observations is small or, in an extreme case, there are none of them at all. Currently, there are about 120 satellites equipped with laser retroreflectors orbiting the Earth. Therefore, the necessity to determine the quality of predictions provided by various analysis centers is important in the context of the increasing number of satellites tracked by SLR stations. We compare the orbit predictions to final GNSS orbits, precise orbits of geodetic satellites based on SLR measurements determined in postprocessing, and kinematic orbits of low-orbiting satellites based on GPS data. We assess the quality degradation of the orbit predictions over time depending on the type of orbit and the satellite being analyzed. We estimate the time of usefulness of prediction files, and indicate those centers which publish most accurate predictions of the satellites’ trajectories. The best-quality predictions for geodetic satellites and Galileo reach the mean error of 0.5–1 m for the whole 5-day prediction file (for all three components), while the worst ones can reach values of up to several thousand meters during the first day of the prediction.
For over 25 years, the International GNSS Service (IGS) has been processing observational data from the Global Navigation Satellite Systems (GNSSs). Hence, long time series of station coordinates are available, however, they are burdened with discontinuities, station velocity changes, and gross errors. Discontinuities and periodic variations are caused by equipment changes at stations, earthquakes, geophysical processes, data problems, as well as local environmental changes. As a result, many approaches have been identified that identify and remove discontinuities in the GNSS coordinate time series. One of them is the program Finding Outliers and Discontinuities In Time Series (FODITS) implemented in the Bernese GNSS Software environment (Dach et al., 2015), developed by the Astronomical Institute, University of Bern. The program is designed for the automatic analysis of time series, in which the functional model is adapted to the time series of coordinates depending on the adopted parameters. This study presents the analysis of long-term GNSS coordinate time series reprocessed in the framework of the realization of the International Terrestrial Reference Frame 2014 (ITRF2014) using the FODITS program. The results show that the optimum confidence level for the autonomous detection of station discontinuities in FODITS is 99 % and 98 %, for 7-day and 3-day GNSS solutions, respectively, when compared to the manual discontinuity detection from ITRF2014. However, the manual analysis unsupported by statistical tests as conducted in ITRF2014 may contain errors over which further elaboration is indispensable. On the other hand, routine interpretation of GNSS coordinate time series in a fully autonomous manner, although much faster, is not free from drawbacks, in particular in detecting appropriate epochs of discontinuities and changes in station velocities.
The EUREF Permanent GNSS Network (EPN) provides the users with data and products such as station coordinate time series. These are subject to possible discontinuities and trend changes, being earthquake events one of the possible natural causes for these variations. We present here a fully automated tool for the analysis of the coordinate time series of EPN stations located in the desired neighborhood of an earthquake epicenter. The tool is made freely available to the public and applied here to two significant earthquake events occurred in Europe in recent years, where several trend changes and jumps are easily revealed.
Artykuł przedstawia podstawy teorii przerywanej równowagi sformułowanej jako alternatywne względem gradualistycznego darwinizmu ujęcie przebiegu makroewolucji. Twórcami teorii przerywanej równowagi są amerykańscy paleontologowie Stephen Jay Gould i Niles Eldredge, według których proces makroewolucji nie zachodzi stopniowo, małymi kroczkami, lecz charakteryzuje się długimi okresami stazy, które co jakiś czas przerywane są szybkimi - w skali geologicznej - przemianami organizmów.
Satellite laser ranging (SLR) measurements play a key role in determining global geodetic parameters, such as station coordinates, geocenter motion, low-degree Earth’s gravity field parameters, and Earth rotation parameters. Currently, the observations to the two LAser GEOdynamics Satellites (LAGEOS) and two Etalon satellites provide operational standard products and contribute to the realization of the scale and the origin of the International Terrestrial Reference Frame (ITRF). Nowadays under consideration is an extension of the ITRF realizations by including LAser RElativity Satellite (LARES). In July 2022, the LARES-2 satellite was launched with the main purpose to verify fundamental physics, especially the Lense-Thirring effect emerging from General Relativity. We simulate orbits and observations for the LARES-2 satellite, as well as the LARES-like satellites, which complement the current constellation of LAGEOS-1/-2 and LARES-1/-2 using the butterfly configuration. We assess the impact of the observations to satellites with different orbital parameters on the determination of global geodetic parameters. We show that placing a satellite in a retrograde orbit – orbiting against the Earth’s rotation at a high altitude of 5600 km, can substantially improve the quality of the global geodetic parameters. The LAGEOS-1/-2 + LARES-1/-2/-4 solution achieves the 3D mean error at the level of 1.62 mm for the station coordinates, and mean errors of 0.7, 0.7, and 1.3 mm for the X, Y, and Z geocenter components, respectively, bringing us closer to fulfilling the requirements established by the Global Geodetic Observations System (GGOS) of 1 mm accuracy for the reference frame stability.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.