Multipath is one of the major source of errors in precise Global Navigation Satellite System positioning. With the emergence of new navigation systems, such as Galileo, upgraded signals are progressively being used and are expected to provide greater resistance to the effects of multipath compared to legacy Global Positioning System (GPS) signals. The high quality of Galileo observations along with recent development of the Galileo space segment can therefore offer significant advantages to Galileo users in terms of the accuracy and reliability of positioning. The aim of this paper is to verify this hypothesis. The multipath impact was determined both for code and phase measurements as well as for positioning results. The code multipath error was determined using the Code-Minus-Carrier combination. The influence of multipath on phase observations and positioning error was determined using measurements on a very short baseline. In addition, the multipath was classified into two different types: specular and diffuse, using wavelet transform. The results confirm that the Galileo code observations are more resistant to the multipath effect than GPS observations. Among all of the observations examined, the lowest values of code multipath errors were recorded for the Galileo E5 signal. However, no advantage of Galileo over GPS was observed for phase observations and for the analysis of positioning results.

The stochastic model, together with the functional model, form the mathematical model of observation that enables the estimation of the unknown parameters. In Global Navigation Satellite Systems (GNSS), the stochastic model is an especially important element as it affects not only the accuracy of the positioning model solution, but also the reliability of the carrier-phase ambiguity resolution (AR). In this paper, we study in detail the stochastic modeling problem for Multi-GNSS positioning models, for which the standard approach used so far was to adopt stochastic parameters from the Global Positioning System (GPS). The aim of this work is to develop an individual, empirical stochastic model for each signal and each satellite block for GPS, GLONASS, Galileo and BeiDou systems. The realistic stochastic model is created in the form of a fully populated variance-covariance (VC) matrix that takes into account, in addition to the Carrier-to-Noise density Ratio (C/N${}_0$)-dependent variance function, also the cross- and time-correlations between the observations. The weekly measurements from a zero-length and very short baseline are utilized to derive stochastic parameters. The impact on the AR and solution accuracy is analyzed for different positioning scenarios using the modified Kalman Filter. Comparing the positioning results obtained for the created model with respect to the results for the standard elevation-dependent model allows to conclude that the individual empirical stochastic model increases the accuracy of positioning solution and the efficiency of AR. The optimal solution is achieved for four-system Multi-GNSS solution using fully populated empirical model individual for satellite blocks, which provides a 2% increase in the effectiveness of the AR (up to 100%), an increase in the number of solutions with errors below 5 mm by 37% and a reduction in the maximum error by 6 mm compared to the Multi-GNSS solution using the elevation-dependent model with neglected measurements correlations.

The method of precise GNSS positioning using corrections from a network of reference stations, the so-called Network RTK, is currently the most accurate real time kinematic positioning method. The reliability of this method is largely dependent on the accuracy of determination of network ionospheric and geometric corrections (taking into account the tropospheric refraction and orbit errors). There are many indexes describing the reliability of Network RTK positioning in the aspect of the accuracy of modelling these errors. The so-called solution quality indicators are used for this purpose. They are parameters determined in the central network pre-processing which provide quantitative information regarding the predicted reliability of the positioning in an area encompassed by a network of reference stations. Unfortunately, their interpretation is hindered due to the lack of connection with basic parameters describing precise positioning quality, i.e. the correctness of the carrier phase ambiguity resolution and the accuracy of the rover position. This study presents a new approach to the design of quality indicators for the Network RTK method, based on a quantitative description of two parameters—solution accuracy and availability. The presented method is based on the existing parameters describing the probability of the correct fixing of ambiguities and the estimation of the fixed baseline solution accuracy. However, a stochastic model of observation, taking into account the accuracy of network corrections is used for these calculations. The proposed method enables a full account of all parameters affecting the reliability of positioning, which is not possible with the currently applied methods. Numerical tests of the new indicators carried out for a part of the regional reference stations network confirmed the effectiveness of this approach. The proposed indicators provide much more clear identification of the time periods for which the reliability of the solution was lower compared to the existing quality indexes which indications were unclear and inaccurate.

In the framework of the regional EURAMET.M.G-K2 comparison of absolute gravimeters, 17 gravimeters were compared in November 2015. Four gravimeters were from different NMIs and DIs, they were used to link the regional comparison to the CCM.G.K2 by means of linking converter. Combined least-squares adjustments with weighted constraint was used to determine KCRV. Several pilot solutions are presented and compared with the official solution to demonstrate influences of different approaches (e.g. definition of weights and the constraint) on results of the adjustment. In case of the official solution, all the gravimeters are in equivalence with declared uncertainties. Main text To reach the main text of this paper, click on Final Report . Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/ . The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Continuously operating reference station (CORS) networks, as one of the fundamental segments of the precise global navigation satellite systems (GNSSs) positioning techniques, have been undergoing rapid development and growth in the last two decades. The existing and newly created CORS networks coincide with both the services provided and the covered area. This is the situation in Poland, where there are five nation-wide and local networks that have in total over 500 stations and provide access to similar GNSS data, real time kinematic (RTK), and network real time kinematic (NRTK) services. This paper presents one of the most comprehensive tests conducted to evaluate the quality of network-based GNSS positioning services performance provided by all CORS networks available in Poland. The test was performed in November 2017 and included the analysis of accuracy and reliability of positioning performance, time to first fix (TTFF), an average age of correction as well as the compliance of the reference frame realization. The test data were obtained from the field measurements of consecutive RTK/NRTK services and simultaneous continuous measurements carried out at 20 reference points of the first-order geodetic network, evenly distributed throughout Poland. Obtained results allowed to estimate the positioning performance accuracy and reliability for all tested streams and their mutual comparison of quality along with the analysis of the reference frame realization compliance implemented by all networks. In most cases, the results confirm the nominal accuracy of positioning (at 68% confidence level) based on tested streams of 1 cm for horizontal and 2 cm for vertical components. However, it was also found that for some networks and streams the obtained accuracy was twice lower (reaching up to 4 cm for the height component), and compliance with the vertical reference frame is lower.

The concept of global navigation satellite system (GNSS) real-time kinematic (RTK) positioning through the use of multiple reference stations (Network RTK) is the most common approach to relative positioning, which makes it possible to achieve centimeter-level accuracy for medium baselines. In this approach, ionospheric and geometric correction terms, generated on the basis of a model of interpolation of the distance-dependent biases, are applied to the functional model of rover positioning. The accuracy and reliability of Network RTK performance depend on the accuracy of the defined correction terms. Especially during storm-level ionospheric activity, the applied spatial interpolation model might not be suitable for the real ionospheric state, causing the ambiguity resolution to be less reliable, or even impossible, because of high residual errors. Thus, the residual errors can substantially degrade the correctness of the functional model and should be accounted for to obtain optimal estimation o...