rss_2.0Artificial Satellites FeedSciendo RSS Feed for Artificial Satellites Satellites 's Cover Augmentation Factor of Precision in Gnss<abstract> <title style='display:none'>Abstract</title> <p>The dilution of precision (DOP) in satellite navigation system provides a simple characterization of the user–satellite geometry and a quantitative assessment of the positioning constellation configuration. The essential idea of physical augmentation factor of precision (PAFP) proposed in this work, is that navigation signals are transmitted at multiple frequencies from each visible satellite in the positioning constellation, while users measure the corresponding multiple pseudoranges of satellites to achieve high precision code positioning. As the multiple pseudoranges of one satellite are measured independently by the corresponding navigation signals at different frequencies, it is reasonable to treat the measurement errors due to the satellite clock and ephemeris, the atmospheric propagation as uncorrelated, random, and identically distributed. The multipath effects and receiver noise are also processed with some empirical models. By measuring user–satellite code pseudoranges at different frequencies, the PAFP offers a scheme that produces the same effect as that of the redundant-overlapping constellation, thus equivalently improving the geometric DOP. It can effectively improve code positioning precision of satellite navigation system.</p> </abstract>ARTICLE2022-10-21T00:00:00.000+00:00Land Vehicle Navigation Using Low-Cost Integrated Smartphone GNSS Mems and Map Matching Technique<abstract> <title style='display:none'>Abstract</title> <p>The demand for smartphone positioning has grown rapidly due to increased positioning accuracy applications, such as land vehicle navigation systems used for vehicle tracking, emergency assistance, and intelligent transportation systems. The integration between navigation systems is necessary to maintain a reliable solution. High-end inertial sensors are not preferred due to their high cost. Smartphone microelectromechanical systems (MEMS) are attractive due to their small size and low cost; however, they suffer from long-term drift, which highlights the need for additional aiding solutions using road network that can perform efficiently for longer periods. In this research, the performance of the Xiaomi MI 8 smartphone’s single-frequency precise point positioning was tested in kinematic mode using the between-satellite single-difference (BSSD) technique. A Kalman filter algorithm was used to integrate BSSD and inertial navigation system (INS)-based smartphone MEMS. Map matching technique was proposed to assist navigation systems in global navigation satellite system (GNSS)-denied environments, based on the integration of BSSD–INS and road network models applying hidden Marcov model and Viterbi algorithm. The results showed that BSSD–INS–map performed consistently better than BSSD solution and BSSD–INS integration, irrespective of whether simulated outages were added or not. The root mean square error (RMSE) values for 2D horizontal position accuracy when applying BSSD–INS–map integration improved by 29% and 22%, compared to BSSD and BSSD–INS navigation solutions, respectively, with no simulated outages added. The overall average improvement of proposed BSSD–INS–map integration was 91%, 96%, and 98% in 2D horizontal positioning accuracy, compared to BSSD–INS algorithm for six GNSS simulated signal outages with duration of 10, 20, and 30 s, respectively.</p> </abstract>ARTICLE2022-10-21T00:00:00.000+00:00Relativistic Effects in the Rotation of Dwarf Planets and Asteroids<abstract> <title style='display:none'>Abstract</title> <p>The effect of the geodetic rotation (which includes two relativistic effects: geodetic precession and geodetic nutation) is the most significant relativistic effect in the rotation of the celestial bodies. For the first time in this research, this relativistic effect is determined in the rotation of dwarf planets (Ceres, Pluto, and Charon) and asteroids (Pallas, Vesta, Lutetia, Europa, Ida, Eros, Davida, Gaspra, Steins, and Itokawa) in the Solar System with known values of their rotation parameters. Calculations of the values of their geodetic rotation are made by a method for studying any bodies in the Solar System with a long-term ephemeris. Values of geodetic precession and geodetic nutation for all these celestial bodies were calculated in ecliptic Euler angles relative to their proper coordinate systems and in their rotational elements relative to the fixed equator of the Earth and the vernal equinox (at the epoch J2000.0). The obtained analytical values of the geodetic rotation for the celestial bodies can be used to numerically investigate their rotation in the relativistic approximation, and also used to estimate the influence of relativistic effects on the orbital–rotational dynamics for the bodies of exoplanetary systems.</p> </abstract>ARTICLE2022-10-21T00:00:00.000+00:00A Script-Driven Approach to Mapping Satellite-Derived Topography and Gravity Data Over the Zagros Fold-and-Thrust Belt, Iran<abstract> <title style='display:none'>Abstract</title> <p>Integrated geophysical mapping benefits from visualizing multi-source datasets including gravity and satellite altimetry data using 2D and 3D techniques. Applying scripting cartographic approach by R language and GMT supported by traditional mapping in QGIS is presented in this paper with a case study of Iranian geomorphology and a special focus on Zagros Fold-and-Thrust Belt, a unique landform of the country affected by complex geodynamic structure. Several modules of GMT and ’tmap’ and ’raster’ packages of R language were shown to illustrate the efficiency of the console-based mapping by scripts. Data sources included high-resolution raster grids of GEBCO/SRTM, EGM-2008, SRTM DEM and vector geologic layers of USGS. The cartographic objective was to visualize thematic maps of Iran: topography, geology, satellite-derived gravity anomalies, geoid undulations and geomorphology. Various cartographic techniques were applied to plot the geophysical and topographic field gradients and categorical variations in geological structures and relief along the Zagros Fold-and-Thrust Belt. The structures of Elburz, Zagros, Kopet Dag and Makran slopes, Dasht-e Kavir, Dasht-e Lut and Great Salt Desert were visualized using 3D-and 2D techniques. The geomorphometric properties (slope, aspect, hillshade, elevations) were modelled by R. The study presented a series of 11 new maps made using a combination of scripting techniques and GIS for comparative geological-geophysical analysis. Listings of R and GMT scripting are provided for repeatability.</p> </abstract>ARTICLE2022-07-28T00:00:00.000+00:00QHY-174M-GPS Camera as the Device for Photometry of Artificial Satellites<abstract> <title style='display:none'>Abstract</title> <p>In this paper, we make an attempt to use the QHY174M-GPS camera for the photometry research of fast-rotating artificial objects including debris, satellites and rocket bodies. This device is useful for imaging occultations, eclipses, meteors, and so on due to a highly precise recording of the time (GPS-based) and location of the observation on every frame and fast readout of the CMOS detector. The precision of time registration by the QHY174M-GPS camera is at the level of microseconds. All light curves obtained by studied camera during observations of artificial satellites in this work were carried out at Derenivka Observatory of Uzhhorod National University, Ukraine. The created photometric system with QHY174M-GPS camera as the detector and reflector telescope with parameters D=120mm, F=114mm, FOV=2.82°1.76° was calibrated. For target observations, SharpCap software was used. For the purposes of photometry processing, ccd_phot software was developed using Python 3.8 programming language with astropy and photutils packages. Photometry observations of artificial satellites of the Earth and standard stars were carried out. Over 80 lightcurves of artificial satellites were obtained. Comparing synchronous observations from two sites, separated 15 km from each other, we can conclude that photometry on the QHY174M-GPS camera gave us the same shape of lightcurve and additional advantages, such as time of exposure or simplicity of usage.</p> </abstract>ARTICLE2022-04-22T00:00:00.000+00:00Geodetic Precession of the Sun, Solar System Planets, and their Satellites<abstract> <title style='display:none'>Abstract</title> <p>The effect of the geodetic precession is the most significant relativistic effect in the rotation of celestial bodies. In this article, the new geodetic precession values for the Sun, the Moon, and the Solar System planets have been improved over the previous version by using more accurate rotational element values. For the first time, the relativistic effect of the geodetic precession for some planetary satellites (J1–J4, S1–S6, S8–S18, U1–U15, N1, and N3–N8) with known quantities of the rotational elements was studied in this research. The calculations of the values of this relativistic effect were carried out by the method for studying any bodies of the Solar System with long-time ephemeris. As a result, the values of the geodetic precession were first determined for the Sun, planets in their rotational elements, and for the planetary satellites in the Euler angles relative to their proper coordinate systems and in their rotational elements. In this study, with respect to the previous version, additional and corrected values of the relativistic influence of Martian satellites (M1 and M2) on Mars were calculated. The largest values of the geodetic rotation of bodies in the Solar System were found in Jovian satellite system. Further, in decreasing order, these values were found in the satellite systems of Saturn, Neptune, Uranus, and Mars, for Mercury, for Venus, for the Moon, for the Earth, for Mars, for Jupiter, for Saturn, for Uranus, for Neptune, and for the Sun. First of all, these are the inner satellites of Jupiter: Metis (J16), Adrastea (J15), Amalthea (J5), and Thebe (J14) and the satellites of Saturn: Pan (S18), Atlas (S15), Prometheus (S16), Pandora (S17), Epimetheus (S11), Janus (S10), and Mimas (S1), whose values of geodetic precession are comparable to the values of their precession. The obtained numerical values for the geodetic precession for the Sun, all the Solar System planets, and their satellites (E1, M1, M2, J1–J5, J14–J16, S1–S6, S8–S18, U1–U15, N1, and N3–N8) can be used to numerically study their rotation in the relativistic approximation and can also be used to estimate the influence of relativistic effects on the orbital–rotational dynamics of bodies of exoplanetary systems.</p> </abstract>ARTICLE2022-04-22T00:00:00.000+00:00Efficient Cost-Effective Static-PPP Using Mixed GPS/Glonass Single-Frequency Observations (KSA)<abstract> <title style='display:none'>Abstract</title> <p>Precise point positioning (PPP) is a GNSS positioning technique that saves cost and has an acceptable accuracy for enormous applications. PPP proved its efficiency through two decades comparing with traditional differential positioning technique. PPP uses one receiver collecting observations at an unknown station without the need for a reference station with known coordinates. PPP-collected observations must undergo extensive mitigation of different GNSS errors. Static-PPP accuracy depends mainly on the observations type (dual or single frequency), used systems (GPS or GLONASS or mixed GPS/GLONASS), satellites geometry, and observations duration. Static-PPP using dual-frequency observations gives optimum accuracy with a high cost. Static-PPP using single-frequency observations gives acceptable accuracy with a low cost. Since the end of 2012, PPP users are able to depend on GLONASS system as an alternative. This research investigates singe-frequency/static-PPP accuracy variation on KSA based on different factors: the system used (GPS or GLONASS or GPS/GLONASS), satellites geometry, observations duration, and ionosphere activity state. Observations from 2 days reflecting different ionospheric activity states were used for this research from three CORS stations (KSA-CORS network) operated by KSA-General Authority for Survey and Geospatial Information (KSA-GASGI). It can be concluded that precision (0.05 m lat., 0.12 m long., and 0.13 m height) under quiet ionosphere and precision (0.09 m lat., 0.20 m long., and 0.23 m height) under active ionosphere could be attained using 24 h mixed GPS/GLONASS single-frequency observations. Static-PPP using 24 h mixed GPS/GLONASS single-frequency observations’ accuracies are 0.01 m lat., 0.01 m long., and 0.03 m height (quiet ionosphere) and 0.01 m lat., 0.06 m long., and 0.06 m height (active ionosphere) compared to true station coordinates.</p> </abstract>ARTICLE2022-04-22T00:00:00.000+00:00Integration of Artificial Neural Network and the Optimal GNSS Satellites’ Configuration for Improving GNSS Positioning Techniques (A Case Study in Egypt)<abstract> <title style='display:none'>Abstract</title> <p>Nowadays, theglobal navigation satellite system (GNSS) positioning techniques based on the International GNSS Service (IGS) products are extensively used for various precise applications. However, specific conditions such as the dual-frequency observations and the final IGS products are required. Consequently, the absence of the final IGS data and using single-frequency observations will degrade these techniques’ accuracy. In this paper, two algorithms through two separated stages are formulated for improving the single-frequency GNSS observations by using one GNSS receiver based on the broadcast ephemerides in real time or close to real time. The first algorithm represents the preparation stage for the second one. It classifies the observations by separating the optimal values of position dilution of precision (PDOP) and the number of satellites (NOS), as well as the corresponding values of coordinates. The second stage includes an algorithm based on the artificial neural network (ANN) approach, which is set at the ANN variables that produce the best precision through the applied tests at the present study. Binary numbers, log sigmoid-Purelin, cascade forward net, and one hidden layer with a size of 10 neurons are the optimal variables of ANN inputs format, transfer functions constellations, feedforward net type, and the number of hidden layers (NHL) and its size, respectively. The simulation results show that the designed algorithms produce a significant improvement in the horizontal and vertical components. Lastly, an evaluation stage is performed in the case of dual-frequency observations by using broadcast ephemerides. The simulation outputs indicate that the precision at applying the proposed integration is completely enhanced compared with the outputs of IGS final data.</p> </abstract>ARTICLE2022-04-22T00:00:00.000+00:00Reliability of CSRS-PPP for Validating the Egyptian Geodetic Cors Networks<abstract> <title style='display:none'>Abstract</title> <p>The development, utilization, and maintenance of continuously operating reference stations (CORS) network are vital in many areas of surveying and geodesy, such as controllinggeodetic networks, developinglocal ionospheric models, and estimating the tectonic plate movements. Accordingly, the Egyptian Surveying Authority (ESA) established a CORS network consisting of 40 stations covering the Nile valley and its delta in 2011. CORS collect global navigation satellite system (GNSS) data. Recently, Egypt has witnessed rapid growth in many infrastructure projects and the development of new cities on a national scale. Therefore, there is an urgent need to investigate the ESA-CORS accuracy; the quality of data from the ESA-CORS must be considered for monitoring continuous tectonic motion, coordinating changes, and for Egypt’s development plan. Contemporary research worldwide identified considerable benefits of the precise point positioning (PPP) solution of dual- or single-frequency GNSS data. This study investigates the reliability of using the CSRS-PPP service for three consecutive observation days of 32 ESA-CORS networks in Egypt and the surrounding six international GNSS services (IGS)-CORS. For ESA-CORS, the PPP solution showed a root mean square error (RMSE) value of 6 mm (standard deviation [SD] = 3–4 mm) in east and north; for the height direction, the solution indicated an RMSE value of 22 mm (SD was about 14 mm). At a confidence level of 95%, this study revealed that SD95% was 2 mm in east and north directions and 6–7 mm for the height direction. This study shows that the PPP solution shown from the ESA-CORS stations is associated with two times better for horizontal and four times for the height direction than the delivered form ESA-CORS stations.</p> </abstract>ARTICLE2022-04-22T00:00:00.000+00:00Measurements to Space Debris in 2016–2020 by Laser Sensor at Borowiec Poland<abstract><title style='display:none'>Abstract</title><p>In 2014, a significant upgrade was made to the Borowiec (BORL 7811) laser-ranging system, which is the part of Space Research Centre of the Polish Academy of Sciences (SRC PAS). Two high-energy lasers modules were installed. First is the EKSPLA PL-2250, used for tracking objects equipped with retroreflectors. Second is the Continuum Surelite III, dedicated to the tracking of space debris without retroreflectors. In 2016, the BORL station joined the space debris tracking laser group and, since then, is tracking systematically inactive/defunct satellites and typical rocket bodies from LEO regime. Today, the BORL is tracking regularly about 80 different space debris objects. The paper presents the activity of the BORL laser station in observations of space debris. The results presented are from years 2016 to 2020. The sum of all passes from this period is almost 2 000, giving over 23 000 normal points. Average root mean square error (RMS) of objects with satellite laser ranging-dedicated (SLR-dedicated) retroreflectors ranges 1.5 cm–14 cm and of objects without SLR-dedicated retroreflectors ranges 8 cm–222 cm.</p></abstract>ARTICLE2022-01-18T00:00:00.000+00:00Evaluation of GGMs Based on the Terrestrial Gravity Disturbance and Moho Depth in Afar, Ethiopia<abstract> <title style='display:none'>Abstract</title> <p>To estimate Moho depth, geoid, gravity anomaly, and other geopotential functionals, gravity data is needed. But, gravity survey was not collected in equal distribution in Ethiopia, as the data forming part of the survey were mainly collected on accessible roads. To determine accurate Moho depth using Global Gravity Models (GGMs) for the study area, evaluation of GGMs is needed based on the available terrestrial gravity data. Moho depth lies between 28 km and 32 km in Afar. Gravity disturbances (GDs) were calculated for the terrestrial gravity data and the recent GGMs for the study area. The model-based GDs were compared with the corresponding GD obtained from the terrestrial gravity data and their differences in terms of statistical comparison parameters for determining the best fit GGM at a local scale in Afar. The largest standard deviation (SD) (36.10 mGal) and root mean square error (RMSE) (39.00 mGal) for residual GD and the lowest correlation with the terrestrial gravity (0.61 mGal) were obtained by the satellite-only model (GO_CONS_GCF_2_DIR_R6). The next largest SD (21.27 mGal) and RMSE (25.65 mGal) for residual GD were obtained by the combined gravity model (XGM2019e_2159), which indicates that it is not the best fit model for the study area as compared with the other two GGMs. In general, the result showed that the combined models are more useful tools for modeling the gravity field in Afar than the satellite-only GGMs. But, the study clearly revealed that for the study area, the best model in comparison with the others is the EGM2008, while the second best model is the EIGEN6C4.</p> </abstract>ARTICLE2021-10-08T00:00:00.000+00:00Distance Between Two Keplerian Orbits<abstract> <title style='display:none'>Abstract</title> <p>In this paper, constrained minimization for the point of closest approach of two conic sections is developed. For this development, we considered the nine cases of possible conics, namely, (elliptic–elliptic), (elliptic–parabolic), (elliptic–hyperbolic), (parabolic–elliptic), (parabolic–parabolic), (parabolic–hyperbolic), (hyperbolic–elliptic), (hyperbolic–parabolic), and (hyperbolic–hyperbolic). The developments are considered from two points of view, namely, analytical and computational. For the analytical developments, the literal expression of the minimum distance equation (S) and the constraint equation (G), including the first and second derivatives for each case, are established. For the computational developments, we construct an efficient algorithm for calculating the minimum distance by using the Lagrange multiplier method under the constraint on time. Finally, we compute the closest distance S between two conics for some orbits. The accuracy of the solutions was checked under the conditions that <italic>L</italic>|<italic><sub>solution</sub></italic> ≤ ɛ<sub>1</sub>; <italic>G</italic>|<italic><sub>solution</sub></italic> ≤ ɛ<sub>2</sub>, where ɛ<sub>1,2</sub> &lt; 10<sup>−10</sup>. For the cases of (parabolic–parabolic), (parabolic–hyperbolic), and (hyperbolic–hyperbolic), we studied thousands of comets, but the condition of the closest approach was not met.</p> </abstract>ARTICLE2021-10-08T00:00:00.000+00:00Performance Assessment of Real-Time Multiconstellation GNSS PPP Using a Low-Cost Dual-Frequency GNSS Module<abstract> <title style='display:none'>Abstract</title> <p>The release of low-cost dual-frequency (DF) global navigation satellite system (GNSS) modules provides an opportunity for low-cost precise positioning to support autonomous vehicle applications. The new GNSS modules support the US global positioning system (GPS) L1C/L2C or L5 civilian signals, the Russian GNSS <italic>Globalnaya Navigazionnaya Sputnikovaya Sistema</italic> (GLONASS) L1/L2, Europe’s GNSS Galileo E1/E5b, and Chinese GNSS BeiDou B1/B2 signals. The availability of the DF measurements allows for removal of the ionospheric delay, enhancing the obtained positioning accuracy. Unfortunately, however, the L2C signals are only transmitted by modernized GPS satellites. This means that fewer GPS DF measurements are available. This, in turn, might affect the accuracy and the convergence of the GPS-only precise point positioning (PPP) solution. Multi-constellation GNSS PPP has the potential to improve the positioning accuracy and solution convergence due to the high redundancy of GNSS measurements. This paper aims to assess the performance of real-time quad-constellation GNSS PPP using the low-cost u-blox Z9D-F9P module. The assessment is carried out for both open-sky and challenging environment scenarios. Static, simulated-kinematic, and actual field-kinematic trials have been carried out to evaluate real-time PPP performance. Pre-saved real-time precise orbit and clock products from the <italic>Centre National d’Etudes Spatiales</italic> are used to simulate the real-time scenario. It is shown that the quad-constellation GNSS PPP using the low-cost u-blox Z9D-F9P module achieves decimeter-level positioning accuracy in both the static and simulated-kinematic modes. In addition, the PPP solution convergence is improved compared to the dual- and triple-constellation GNSS PPP counterparts. For the actual kinematic trial, decimeter-level horizontal positioning accuracy is achieved through the GPS + GLONASS + Galileo PPP compared with submeter-level positioning accuracy for the GPS + GLONASS and GPS + Galileo PPP counterparts. Additionally, submeter-level vertical positioning accuracy is achieved through the GPS + GLONASS + Galileo PPP compared with meter-level positioning accuracy for GPS + GLONASS and GPS + Galileo PPP counterparts.</p> </abstract>ARTICLE2021-10-08T00:00:00.000+00:00First Results of Time Series Analysis of the Permanent GNSS Observations at Polish EPN Stations Using GipsyX Software<abstract> <title style='display:none'>Abstract</title> <p>The aim of this work is to explore, for the first time in Poland, the possibility of determining Earth’s crust movements from permanent observations at selected permanent stations using the GipsyX software for a period of 8 years (2011–2018) in the ITRF2014 reference frame. The data used in this work are from 15 Aktywna Sieć Geodezyjna (ASG)-EUPOS stations from 2011 to 2018, which are also European Permanent Network (EPN) stations. The stations Borowa Góra, Borowiec, Józefosław, Lamkówko, and Wroclaw are also International Global Navigation Satellite Systems (GNSS) Service (IGS) stations. Daily data, rinex files, for these stations have been made available for this work by the Main Office of Surveying and Cartography. The calculations were made using the GipsyX software in the ITRF14 reference frame. The tests performed have shown that daily solutions from 8-year-long time series give secular trends with an accuracy of 0.01 mm/yr. Our results suggest that there are small differences in horizontal and vertical velocities and in the accuracy estimated between our and EPN solutions. At some stations, for example, Łódź, the differences are much larger. The impact of additional GNSS observations on the accuracy of determination of horizontal and vertical movements of the Earth’s crust shows a submillimeter accuracy in computed coordinates of stations even at a relatively small time interval. It means that multi-GNSS Precise Point Positioning (PPP) processing can be used in the future for the estimation of geodynamic processes.</p> </abstract>ARTICLE2021-10-08T00:00:00.000+00:00Quasi-1500-Year-Cycle Signal in Length-of-Day Change<abstract> <title style='display:none'>Abstract</title> <p>Length-of-day (LOD) change, i.e., variations in Earth’s rotation rate, includes the long-term slowdown trend, as well as periodic and irregular fluctuations. The current continuous sequence of the LOD change covers a time span of &lt;400 years. Using astronomical records in ancient historical documents, combined with a modern astronomical ephemeris, it is possible to obtain ancient LOD change. Some scholars have given a discontinuous LOD data series for the past 4000 years. In this paper, the author uses the Lomb–Scargle periodogram to study the LOD series and finds a significant quasi-1500-year-cycle signal. Furthermore, with weighted wavelet Z-transform, time-varying characteristics of the cycle in the LOD change are obtained.</p> </abstract>ARTICLE2021-08-13T00:00:00.000+00:00In Memoriam: Dr. Eng. Leszek Jaworski (1961–2021) Assessment of PPP-AR Positioning and Zenith Total Delay Estimation with Modernized CSRS-PPP<abstract> <title style='display:none'>Abstract</title> <p>The precise point positioning (PPP) method has become more popular due to powerful online global navigation satellite system (GNSS) data processing services, such as the Canadian Spatial Reference System-PPP (CSRS-PPP). At the end of 2020, the CSRS-PPP service launched the ambiguity resolution (AR) feature for global positioning system (GPS) satellites. More reliable results are obtained with AR compared to the results with traditional ambiguity-float PPP. In this study, the performance of the modernized CSRS-PPP was comparatively assessed in terms of static positioning and zenith total delay (ZTD) estimation. Data for 1 month in the year 2019 obtained from 47 international GNSS service (IGS) stations were processed before and after modernization of the CSRS-PPP. The processes were conducted for GPS and GPS + GLONASS (GLObalnaya NAvigatsionnaya Sputnikovaya Sistema) satellite combinations. Besides, the results were analyzed in terms of accuracy and convergence time. According to the solutions, the AR feature of the CSRS-PPP improved the accuracy by about 50% in the east component for GPS + GLONASS configuration. The root-mean-square error (RMSE) of the ZTD difference between modernized CSRS-PPP service and IGS final troposphere product is 5.8 mm for the GPS-only case.</p> </abstract>ARTICLE2021-08-13T00:00:00.000+00:00Effect of the Gravitational Aberration on the Earth Gravity Field<abstract><title style='display:none'>Abstract</title><p>Discussing the problem of the external gravitational potential of the rotating Earth, we have to consider the fundamental postulate of the finite speed of the propagation of gravitation. This can be done using the expressions for the gravitational aberration compared to the Liénard–Wiechert solution of the retarded potentials. The term gravitational counter-aberration or <italic>co-aberration</italic> is introduced to describe the pattern of the propagation of the gravitational signal emitted by the rotating Earth. It is proved that in the first approximation, the classic theory of the aberration of light can be applied to calculate this effect. Some effects of the gravitational aberration on the external gravity field of the rotating Earth may influence the orbit determination of the Earth artificial satellites.</p></abstract>ARTICLE2021-04-18T00:00:00.000+00:00Study of EGNOS safety of life service during the period of solar maximum activity<abstract><title style='display:none'>ABSTRACT</title><p> The Satellite Base Augmentation System (SBAS) - EGNOS (European Geostationary Navigation Overlay Service) has been certified for Safety of Life (SoL) service for aircraft navigation since 2nd of March 2011. Unfortunately for the territory of Poland, located at the edge of EGNOS service area, the quality of the service corrections are still not sufficient for aircraft navigation requirements. Years 2012 and 2013 are forecasted as a maximum of solar activity in a 11-year solar cycle. This time period will be the chance to perform the first tests for the EGNOS Safety of Life service quality in disturbed ionospheric conditions. During the previous maximum of solar activity, the storm on 30 October 2003 resulted in the inability to use WAAS corrections for more than 12 hours. This was caused by a very large gradient of disturbances and its’ very sharp boundaries - vertical TEC (VTEC) varied from ~ 40 to ~ 120 TECU (TEC units) within an hour (over ~ 150 km distance). These circumstances gave the opportunity to carry out the test flights to examine the navigation parameters obtained for EGNOS SoL service in disturbed ionospheric conditions. The paper presents project proposal of study and analyses of such fundamental navigation parameters as: accuracy of determined position, availability, continuity and integrity, determined for selected disturbances in relation to quiet conditions. It can give a possibility to estimate of the quality of EGNOS SoL service in Polish airspace during the different phases of flight and its resistance to critical ionospheric conditions.</p></abstract>ARTICLE2012-12-14T00:00:00.000+00:00Research on absolute gravity variations in geodynamic laboratory in Książ in the period of 2007- 2011<abstract><title style='display:none'>ABSTRACT</title><p>In 2006 a gravimetric pavilion was installed inside the Geodynamic Laboratory (LG) in Książ. The pavilion was equipped with two pillars intended to serve relative and absolute gravimetric measurements. Installation of measurement platform for absolute gravity measurements inside gravimetric pavilion of LG made it possible to perform four sessions of absolute gravity measurements: two of them in 2007 (June 10-12 and Nov. 21-22), one in 2008 (Apr. 21-22) and one in 2011 (June 19-21). In 2007 the absolute measurements were performed using two FG5 ballistic gravimeters. In April 2007 the measurements were performed by Dr Makinen from Geodetic Institute of Finnish Academy of Science with application of FG5 No. 221 absolute gravimeter. In June 2007 and in the years 2008 and 2011 such gravimetric measurements were performed by the team from Department of Geodesy and Astronomical Geodesy of Warsaw University of Technology using FG5 No. 230 absolute gravimeter. Elaboration of observation sessions from both gravimeters was performed in the Department of Higher Geodesy following the procedures used in constituting of uniform gravimetric system of geodynamic polygons reference. This constituting of gravimetric system comprised inter alia application of identical models of lithospheric tides (global model by Wenzel, 1997) and ocean tides (Schwiderski, 1980) (reduction of absolute measurements with tidal signals). Observations performed during summer of 2007, autumn of 2007, and spring of 2008 and 2011 indicated existence of small changes of absolute gravity of the order of 1 Gal. Maxima of accelerations appear in the spring period, and minima in the autumn period. This effect is connected with the influence of global hydrological factors the annual amplitude of which is ca 1,5 Gal and achieve extreme values in the spring-autumn interval. Very small value of observed amplitude of gravity changes in the period of extreme variability suggests that the observed gravity changes in LG are caused only by global phenomenon. This proves high degree of „independence” of gravimetric measurement base in LG from the local environmental factors such as ground water level variations, ground humidity, impact of snow cover, etc. At this moment the instrumental environment of absolute measurements obtains particular value, especially in the case of the tiltmeters and relative the gravimeter Lacoste&amp; Romberg (LR-648). The relative gravity measurements as performed simultaneously with absolute gravity measurements enable us to determine the local tidal ephemeredes which makes it possible to replace the global tidal modal with ocean tidal model with the more realistic, locally determined tidal parameters (the local tidal ephemeredes).</p></abstract>ARTICLE2012-12-14T00:00:00.000+00:00en-us-1