Polona Pavlovčič Prešeren

Wavelet Neural Network employment for continuous GNSS orbit function construction: Application for the Assisted-GNSS principle

This paper presents a Wavelet Neural Network (WNN) employment for discrete precise ephemerides tabular data of Global Navigation Satellite System (GNSS) orbit approximation to obtain continuous orbit function. Orbit function is essential in positioning and navigation tasks, the advantage of continuity, however, is that it can also be used during GNSS signal interruptions. The essence of WNN continuous orbit construction is single function determination for the entire interval, while the interpolation methods follow several discrete function establishment. Specifically, we investigate the performance of the WNN continuous orbit approximation by comparison with well known polynomial and trigonometric interpolations. The experimental results show that our proposed method is superior to the traditional methods especially near the end of intervals, because they are not subject to large scale function oscillations as in the case of polynomials constructions. We propose a WNN construction using different mother functions of the WNN namely Mexican hat, Morlet function, Gaussian and Daubechies (D4) wavelet. Furthermore best algorithm for regression estimation is described; selection of neurons in the hidden layer of WNN is based on orthogonal least squares algorithm. The main objective of this article is to show that the presented method of orbit function construction could be used for GNSS ephemerides distribution and short-time prediction in the Assisted GNSS-networks.

GPS orbit approximation using radial basis function networks

We present solutions for GPS orbit computation from broadcast and precise ephemerides using a group of artificial neural networks (ANNs), i.e. radial basis function networks (RBFNs). The problem of broadcast orbit correction, resulting from precise ephemerides, has already been solved using traditional polynomial and trigonometric interpolation. As an alternative approach RBFN broadcast orbit correction produces results within the accuracy range of the traditional methods. Our study shows RBFN broadcast orbit correction performs well also near the end of data intervals and for short data spans (~20min). Regarding limitations of polynomial and trigonometric extrapolation, the most significant advantage of using RBFNs over the traditional methods for GPS broadcast orbit approximation arises from its short time prediction capability.

Determination of tropospheric GNSS impacts from a radiosonde data series in Ljubljana: case study from october to december 2017

GNSS observations, tropospheric impacts, standard atmosphere, radiosonde measurements opazovanja GNSS, vpliv troposfere, standardna atmosfera, radiosondažne meritve UDK: 528.28:551.510.52(497.451.1) Klasifikacija prispevka po COBISS.SI: 1.01 Prispelo: 5. 3. 2018 Sprejeto: 26. 8. 2018 DOI: https://doi.org/10.15292/geodetski-vestnik.2018.03.415-429 SCIENTIFIC ARTICLE Received: 5. 3. 2018 Accepted: 26. 8. 2018 Alenka Senica, Oskar Sterle, Polona Pavlovčič Prešeren DOLOČITEV VPLIVA TROPOSfERE NA OPAZOVANJA GNSS IZ NIZA RADIOSONDAžNIH MERITEV V LJUBLJANI OD OKTOBRA DO DECEMBRA 2017 DETERMINATION Of TROPOSPHERIC GNSS IMPACTS fROM A RADIOSONDE DATA SERIES IN LJUBLJANA: CASE STUDY fROM OCTOBER TO DECEMBER 2017

The employment of a radial basis function network for 3D surface modelling

IZVLEČEK SI | E N Polona Pavlovčič Prešeren, Bojan Stopar, Oskar Sterle | MODELIRANJE 3D-PLOSKEV Z NEVRONSKIMI MREŽAMI Z RADIALNIMI BAZNIMI AKTIVACIJSKIMI FUNKCIJAMI | THE EMPLOYMENT OF A RADIAL BASIS FUNCTION NETWORK FOR 3D SURFACE MODELLING | 241-255 | | 242 | | 60/2 | GEODETSKI VESTNIK RE CE NZ IRA NI ČL AN KI | P EE RRE VIE W ED AR TIC LE S

Ionosperic refraction modeling for better autonomous GNSS code positioning: in preparation of solar cycle 24.

This paper describes GNSS-processing optimisation for better autonomous single-point positioning using single frequency code receivers. GNSS processing improvement is carried out in terms of near-real time ionosphere delay modelling, which will be crucial during the upcoming 24th maximum solar cycle. The main scope of this article is to examine how sudden changes in the ionosphere, caused by events on the Sun, affect autonomous single-point positioning in simple navigation tasks. Further, the specific method of ionosphere delay modelling from actual twofrequency receivers, acquiring carrier phase and code observations, is shown. The modelled value of the ionospheric refraction, which is given in GNSS path delay, is further used in point positioning from singlefrequency code instruments. In addition, we show the advantage of GNSS permanent stations that can supply a wide range of users with better ionosphere data in near real time. From actual experiments, the magnitude of the ionospheric impact on each specific 3D position component is shown and further improved using modelled ionosphere delay values. Finally, we show how to improve GNSS position determination from simple single- or two-frequency GNSS code or carrier-phase receivers in differential GNSS method. This study was conducted for preparations for the upcoming solar cycle maximum, expected to be held in May 2013.

Analysis of gnss-rtk instruments testing on the iso 17123-8 instructions

GNSS-instruments (Global Navigation Satellite System) are the standard field surveying equipment (in addition to tachymeter and levels) for geodetic network establishment and detail surveying. As in the case of other geodetic instruments, it is essential to pre-analyse GNSS-receiver quality parameters, obtained from laboratory calibration and/or field testing of the specific instrument and/or measuring method. Thus, the relevance of the results, as indicated by manufacturer, is obtained that may explain the suitability of a specific GNSS-instrument for field measurements. In 2007, the International Organization of Standardization (ISO), Technical Committee 172, Subcommittee 6 (ISO/TC 172/ SC6), presented a comprehensive GNSS field testing procedures for real time measurements, based on statistical evaluation and verification of the manufacturer’s hardware and firmware. The test can be performed anywhere on the field assuming that the test area includes minimal potential influences to GNSS measurements. At the same time, a test does not require any additional processing software, because the test data evaluation is based on elementary statistics. This paper presents the theoretical basis of GNSS instrument testing in accordance with the ISO 17123-8 guidelines and further examination of specific measurements on the selected site. KLJUČNE BESEDE GNSS, calibration, instrument field testing, real time, ISO/TC 172/SC 6, standard ISO 17123-8 GNSS, kalibracija, terensko preizkušanje instrumentov, realni čas, ISO/TC 172/SC 6, standard ISO 17123-8 UDK: 528.512 GNSS:004.057.2 ISO 17123-8:2007 Klasifikacija prispevka po COBISS-u: 1.02 IZVLEČEK GNSS-instrumente (angl. Global Navigation Satellite System) uvrščamo med standardno terensko geodetsko mersko opremo (poleg elektronskih tahimetrov in nivelirjev), ki jo lahko uporabljamo za vzpostavitev geodetskih mrež in za detajlno izmero. Podobno kot pri drugih geodetskih instrumentih moramo tudi pri GNSS-instrumentih pred izmero ovrednotiti parametre kakovosti instrumentarija oziroma metode izmere, ki jih pridobimo s postopki laboratorijske kalibracije in/ali s terenskim preizkušanjem. Tako pridobimo podatek o ustreznosti navedenih tehničnih značilnostih proizvajalca in ovrednotimo primernost uporabe GNSS-instrumentov za konkretne potrebe. Mednarodna organizacija za standarde ISO (angl. International Organization of Standardization) je v okviru tehnične skupine 172 in podskupine 6 (ISO/ TC 172/SC 6) v letu 2007 predstavila postopke preizkušanja GNSS-merskega instrumentarija za določanje položaja v realnem času, ki temeljijo na oceni kakovosti delovanja strojne in programske opreme posameznega instrumenta. Preizkus lahko opravimo kjerkoli na terenu, kjer so zagotovljeni primerni pogoji za izvedbo GNSS-opazovanj predvsem s stališča čim manjših vplivov na opazovanja z izvorom v okolici. Preizkus tudi ne zahteva dodatnega programskega orodja za obdelavo podatkov meritev, saj je statistično vrednotenje rezultatov opazovanj dokaj enostavno. V prispevku opisujemo teoretične podlage preizkusa GNSS-instrumentov po navodilih standarda ISO 17123-8, ki jih uporabimo za praktični preizkus GNSS-instrumenta.