Ionospheric F-layer scintillation observations using COSMIC and COSMIC2 GPS/GNSS radio occultation data

<p>The FormoSat-3/ Constellation Observing System for Meteorology, Ionosphere and Climate (FS3/COSMIC) has been proven a successful mission on performing active limb sounding of the ionosphere using the GPS radio occultation (RO) technique. The follow-on program called FS7/COSMIC2 is in progress with satellite launched on 25 June of 2019 and includes six low-Earth-orbit (LEO) satellites at 24°-inclination and ~720-km orbits to receive multi-channel (1.5GHz and 1.2GHz) GPS and GLONASS satellite signals. The FS7/COSMIC2 can provide about 5,000 GNSS RO observations per day which are increased by a factor of about 5 comparing to FS3/COSMIC and within the region from the geographic equator to the latitude at 40°. We process 1-Hz amplitude data and obtain complete limb-viewing profiles of the undersampling-S4 scintillation index to study global F-layer irregularity morphology. There are a few percent of FS3/COSMIC and FS7/COSMIC2 GPS/GNSS RO observations having >0.09 undersampling S4max values on average. However, seven identified areas Central Pacific Area, South American Area, African Area, European Area, Japan Sea Area, Arctic Area and Antarctic Area have been designated to have a much higher percentage of strong limb-viewing L-band scintillations. Generally, the F-layer scintillation climatology, namely, its variations with each identified zone, altitude, season, and local time have been documented. The large dataset from the FS3/COSMIC and FS7/COSMIC2 programs enable statistical studies on equatorial and low-latitude ionospheric irregularity and their models.</p>

Rigorous propagation of Galileo-based terrestrial scale

<p>Until now, the GPS and GLONASS satellite antenna phase center offsets (PCOs) used within the International GNSS Service (IGS) have been estimated based on the International Terrestrial Reference Frame (ITRF) scale provided by Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI). Therefore, the IGS products have themselves been conventionally aligned to the ITRF scale, hence could not contribute to its realization. However, the disclosure of metadata, including PCOs, for the Galileo satellites by the European GNSS Agency recently opened a unique opportunity to realize an independent GNSS-based terrestrial scale.</p><p>Before its ongoing third reprocessing campaign (repro3), the IGS thus re-evaluated the PCOs of the GPS and GLONASS satellites by fixing the PCOs of the Galileo satellites in multi-GNSS solutions. The repro3 products, based on these re-evaluated PCOs, can provide an independent Galileo-based scale, which could potentially contribute to the scale of the next ITRF2020. However, the re-evaluated GPS and GLONASS PCOs are introduced as known constant values in repro3 without realistic uncertainties. Therefore, finally no realistic uncertainty will be available for the realized terrestrial scale.</p><p>In this study, another re-evaluation of the GPS and GLONASS PCOs based on the Galileo PCOs is carried out, accounting this time for their variability and estimation errors, with the goal to obtain a more rigorous Galileo-based scale with realistic uncertainty, in particular during the pre-Galileo era. For that purpose, daily time series of GPS and GLONASS PCO estimates derived from the repro3 solutions of different IGS Analysis Centers (ACs) are first analyzed. Deterministic and stochastic models of the time series are then introduced in a global adjustment of all GPS and GLONASS PCOs based on the Galileo PCOs. The re-evaluated PCOs – together with their uncertainties – are finally re-injected into the AC terrestrial frame solutions. The analysis of the latter allows a more rigorous evaluation of the Galileo-based scale and its uncertainty and a more sound comparison to the ones realized by SLR and VLBI. The outcome of this study will provide valuable information for the final selection and realization of the ITRF2020 scale.</p>

Diagnostic method for GLONASS onboard transmitters using monitoring system based on small-size reflector antenna

Regular measurements of the power level of the satellite signals make it possible to detect abnormal functioning of the on-board transmitting device. Due to the high complexity, the large mass of the moving units and the presence of a mechanical drive, it is difficult to carry out regular measurements of the power of the signals of the orbital constellation using large-aperture monitoring systems. To monitor the GLONASS satellites, a small-sized non-power system based on a fixed antenna with a diameter of D = 2 m was developed and put into operation, which allows the NSV self-passage through the main beam of the diagram to make regular assessments of the received power level of the radio navigation signal. The aim of the work is to identify malfunctions of the on-board transmitting devices of the full orbital constellation of the GLONASS satellite based on data obtained by a small-sized monitoring system. The analysis of the data obtained in the period from March 22 to August 11, 2020 revealed 6 NSVs with one or two failed on-board amplifiers and 3 NSVs with three, which was later confirmed by telemetry data. The practical significance of the work lies in the development of a method and a working prototype for alternative diagnostics of the onboard transmitting devices of the GLONASS satellite.

Parameters of the Earth’s rotation taken into account in high-precision simulation of the GLONASS satellites motion in the interests of civil consumers

The purpose of the study was to consider the parameters of the Earth’s rotation in solving the problem of high-precision simulation of the GLONASS navigation spacecraft motion. The paper introduces an algorithm for the operation of a program-algorithm complex for predicting the motion of the GLONASS satellite, taking into account the mathematical models recommended by the International Earth Rotation Service. The study presents the results of estimating the influence of the Earth’s pole motion, uneven rotation of the Earth, precession and nutation on the GLONASS satellite orbit in the form of errors for longitudinal range, vertical and lateral range. The values of the disturbing accelerations and the degree of their influence on the motion of the GLONASS satellite were estimated. The results of deviations of the orbital parameters are obtained: semi-major axis, eccentricity, inclination, longitude of the ascending node, the argument of the pericenter and the focal parameter at an interval of 30 days under the influence of the parameters of the Earth’s orientation.

Validation of the EGSIEM-REPRO GNSS Orbits and Satellite Clock Corrections

In the framework of the European Gravity Service for Improved Emergency Management (EGSIEM) project, consistent sets of state-of-the-art reprocessed Global Navigation Satellite System (GNSS) orbits and satellite clock corrections have been generated. The reprocessing campaign includes data starting in 1994 and follows the Center for Orbit Determination in Europe (CODE) processing strategy, in particular exploiting the extended version of the empirical CODE Orbit Model (ECOM). Satellite orbits are provided for Global Positioning System (GPS) satellites since 1994 and for Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS) since 2002. In addition, a consistent set of GPS satellite clock corrections with 30 s sampling has been generated from 2000 and with 5 s sampling from 2003 onwards. For the first time in a reprocessing scheme, GLONASS satellite clock corrections with 30 s sampling from 2008 and 5 s from 2010 onwards were also generated. The benefit with respect to earlier reprocessing series is demonstrated in terms of polar motion coordinates. GNSS satellite clock corrections are validated in terms of completeness, Allan deviation, and precise point positioning (PPP) using terrestrial stations. In addition, the products herein were validated with Gravity Recovery and Climate Experiment (GRACE) precise orbit determination (POD) and Satellite Laser Ranging (SLR). The dataset is publicly available.

Refining GPS/GLONASS Satellite Clock Offset Estimation in the Presence of Pseudo-Range Inter-Channel Biases

Because of the frequency division multiple access (FDMA) technique, Russian global navigation satellite system (GLONASS) observations suffer from pseudo-range inter-channel biases (ICBs), which adversely affect satellite clock offset estimation. In this study, the GLONASS pseudo-range ICB is treated in four different ways: as ignorable parameters (ICB-NONE), polynomial functions of frequency (ICB-FPOL), frequency-specific parameters (ICB-RF), and satellite-specific parameters (ICB-RS). Data from 110 international global navigation satellite system (GNSS) service stations were chosen to obtain the ICBs and were used for satellite clock offset estimation. The ICBs from the different schemes varied from −20 ns to 80 ns. The ICB-RS model yielded the best results, improving the clock offset accuracy from 300 ps to about 100 ps; it could improve the GLONASS precise point positioning (PPP) accuracy and the converging time by approximately 50% and 30%, respectively. Along similar lines, we introduced the GPS-ICB parameters in the process of GPS satellite clock estimation and GPS/GLONASS PPP, as ICBs may exist for GPS because of different chip shape distortions among GPS satellites. This possibility was found to be the case. Further, the GPS-ICB magnitude ranged from −2 ns to 2 ns, and the estimated satellite clock offsets could improve the accuracy of the GPS and combined GPS/GLONASS PPP by 10%; it also accelerated the converging time by more than 15% thanks to the GPS-ICB calibration.

The Research Into the Integrity Parameter in Air Transport Using GLONASS Data

The article presents the results of the integrity parameter of the GLONASS satellite positioning system in civil aviation. As a source material for the research the authors used observation and navigation data of the GLONASS system from the onboard GNSS receiver mounted on the Cessna 172. In the research, the authors used a model to determine the aircraft position based on the single-frequency SPP code method for GLONASS L1-C/A observations. The numerical calculations were conducted in the RTKLIB software, in the RTKPOST library. The obtained results are interesting from the point of using an application of the GLONASS system in aviation and the possible implementation of the single-frequency GLONASS code observations in the SPP model in order to determine the aircraft position. On the basis of the obtained results it was found that the GLONASS integrity performance data can be used in a procedure of non-precision approach to landing NPA GNSS.