Comparative analysis of positioning deviations using various GNSS systems

Uporaba sustava GLONASS (rus. GLObal’naya NAvigatsionnaya Sputnikovaya Sistema – GLONASS), BeiDou i Galileo očituje se u sve većem broju aplikacija i usluga, gdje se donedavno koristio samo Globalni sustav za određivanje položaja (engl. Global Positioning System - GPS). U pomorstvu, satelitska navigacija predstavlja primarno sredstvo za određivanje položaja na brodovima, kao i jednu od glavnih komponenti integriranih unutar osnovne navigacijske opreme. Ovo, naravno, nije prva studija ovakve vrste. Istraživanje je obuhvatilo blisko područje, danas – u vrijeme kada se smatra da su svi sustavi potpuno operativni. Odstupanja geografske širine, geografske dužine i nadmorske visine analizirana su u razdoblju od sedam uzastopnih dana, od 1. siječnja do 7. siječnja 2021. godine. Procjena se temeljila na tri stanice EUREF (engl. Regional Reference Frame Sub-Commission for Europe – EUREF) mreže referentnih stanica - Budimpešte, Mađarska (BUTE00HUN), Sarajeva, Bosna i Hercegovina (SRJV00BIH) i Podgorice, Crna Gora (DGOR00MNE). Korištene su uobičajene matematičke procedure određivanja položaja kao i formulacije pseudoudaljenosti. Rezultati su prikazani putem srednjih vrijednosti (engl. Mean), standardnih devijacija (engl. Standard Deviation - SD) i interkvartilnih razlika (engl. Interquartilerange - IQR) vrijednosti odstupanja pozicioniranja utvrđenih jednofrekventnim rješenjima za pozicioniranje, kao i broja satelita (engl. Number of satellites - NSAT) i analizom geometrijske razdiobe točnosti (engl. Dilution of Precision - DOP). Doprinos troposferskog i ionosferskog kašnjenja proračunu pogreške pozicioniranja procijenjen je za svaki od sustava zasebno. Ukratko, korištena su četiri sustava, zajedno s kombinacijom svih sustava u četiri različita scenarija. Imajući na umu da je istraživanje bilo prilično kratko, provedeno na rezultatima u samo sedam dana, treba biti oprezan u proglašavanju „najboljih“ i „najgorih“ sustava. No, na temelju prikupljenih podataka može se zaključiti da je, osim očite kombinacije svih sustava, GPS najpouzdaniji sustav na svim postajama. U budućnosti bi se moglo provesti istraživanje s različitim svemirskim vremenskim uvjetima, te ako podaci konačno postanu dostupni, istraživanje bi se moglo provesti i na hrvatskim stanicama.The utilization of GLONASS (rus. GLObal’naya NAvigatsionnaya Sputnikovaya Sistema – GLONASS), BeiDou and Galileo satellite navigation systems is manifesting in a growing number of applications and services, where until recently only Global Positioning System (GPS) was used. In maritime, satellite navigation represents the primary positioning means on-board vessels, as well as one of the main components integrated with essential navigational equipment. This, of course, is not the first study of its kind. The research covered an area close to us, now, as stated before, that all systems are considered to be fully operational. Latitude, longitude and height deviations were analysed during seven consecutive days, in the period 1-7 January 2021. The evaluation was based on multi-GNSS ground-truth data from three European Reference Frame Permanent GNSS Network (EUREF) stations: Budapest, Hungary (BUTE00HUN), Sarajevo, Bosnia and Herzegovina (SRJV00BIH), and Podgorica, Montenegro (DGOR00MNE). Common mathematical positioning procedures were used as well as the pseudorange formulation. The results were presented in terms of mean, standard deviation and IQR values of positioning deviations as determined with single-frequency positioning solutions, together with analysis of number of satellites and Dilution of Precision (DOP). The tropospheric and ionospheric delay contribution to the positioning error budget was evaluated for each of the systems separately. To summarise, four systems were used along with the combination of all systems in four different scenarios. Bearing in mind that this was a fairly short research conducted on the results across only seven days, we must be careful in proclaiming the „best“ and “worst” systems. However, using the gathered data we saw that apart from the obvious combination of all systems, GPS and Galileo were the most reliable systems across all stations. In the future, a research with different space weather conditions could be conducted. Also, if the data finally becomes available, the research could be conducted with Croatian stations as well