D. Próchniewicz

A new study of describing the reliability of GNSS Network RTK positioning with the use of quality indicators

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.

STUDY ON THE INFLUENCE OF STOCHASTIC PROPERTIES OF CORRECTION TERMS ON THE RELIABILITY OF INSTANTANEOUS NETWORK RTK

ABSTRACT The reliability of precision GNSS positioning primarily depends on correct carrier-phase ambiguity resolution. An optimal estimation and correct validation of ambiguities necessitates a proper definition of mathematical positioning model. Of particular importance in the model definition is the taking into account of the atmospheric errors (ionospheric and tropospheric refraction) as well as orbital errors. The use of the network of reference stations in kinematic positioning, known as Network-based Real-Time Kinematic (Network RTK) solution, facilitates the modeling of such errors and their incorporation, in the form of correction terms, into the functional description of positioning model. Lowered accuracy of corrections, especially during atmospheric disturbances, results in the occurrence of unaccounted biases, the so-called residual errors. The taking into account of such errors in Network RTK positioning model is possible by incorporating the accuracy characteristics of the correction terms into the stochastic model of observations. In this paper we investigate the impact of the expansion of the stochastic model to include correction term variances on the reliability of the model solution. In particular the results of instantaneous solution that only utilizes a single epoch of GPS observations, is analyzed. Such a solution mode due to the low number of degrees of freedom is very sensitive to an inappropriate mathematical model definition. Thus the high level of the solution reliability is very difficult to achieve. Numerical tests performed for a test network located in mountain area during ionospheric disturbances allows to verify the described method for the poor measurement conditions. The results of the ambiguity resolution as well as the rover positioning accuracy shows that the proposed method of stochastic modeling can increase the reliability of instantaneous Network RTK performance.

Network-Based Stochastic Model for Instantaneous GNSS Real-Time Kinematic Positioning

AbstractThe 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...

Participation of employees and students of the Faculty of Geodesy and Cartography in polar research

Abstract This year the Faculty of Geodesy and Cartography, Warsaw University of Technology celebrates its 95th jubilee, which provides an opportunity to present the Faculty’s rich traditions in polar research. Employees and students of the faculty for almost 60 years have taken part in research expeditions to the polar circle. The article presents various studies typical of geodesy and cartography, as well as miscellany of possible measurement applications and geodetic techniques used to support interdisciplinary research. Wide range of geodetic techniques used in polar studies includes classic angular and linear surveys, photogrammetric techniques, gravimetric measurements, GNSS satellite techniques and satellite imaging. Those measurements were applied in glaciological, geological, geodynamic, botanical researches as well as in cartographic studies. Often they were used in activities aiming to ensure continuous functioning of Polish research stations on both hemispheres. This study is a short overview of thematic scope and selected research results conducted by our employees and students.

Geodetic and Geodynamic Studies at Department of Geodesy and Geodetic Astronomy Wut

Abstract The article presents current issues and research work conducted in the Department of Geodesy and Geodetic Astronomy at the Faculty of Geodesy and Cartography at Warsaw University of Technology. It contains the most important directions of research in the fields of physical geodesy, satellite measurement techniques, GNSS meteorology, geodynamic studies, electronic measurement techniques and terrain information systems.