In recent years GNSS measurements techniques obtained a majority role in civil engineering and other technical fields. An example of this is the monitoring of both natural phenomena and manmade ...constructions. The main advantages of satellite positioning, as opposite to classical surveying techniques like levelling or total stations, are continuous long term observations and economic advantage, due to the lack of measurement crew. Currently, apart from GPS, other satellite systems in use like GLONASS or Galileo are becoming more important. Together with development of GNSS measurements for satellite positioning in open areas, also urban and mountainous areas can be measured. This kind of areas was excluded from measurements with single GNSS system, due to the lack of the required minimum number of visible satellites. Multi-GNSS (hybrid, integrated - usage of more than one satellite navigation system in measurements) positioning, currently providing more than 80 active satellites, opens new grounds for satellite measurements. Among measurement methods PPP is the most developing one since the beginning of 21st century. Main PPP advantages are: independence from reference station, lack of limitation of use to certain areas and global coverage with consistent, homogenous solutions. The paper shows the results of 90-days continuous static observations processed with the usage of PPP technique on simulated different sky view conditions. Measurements were made on points with known coordinates as a construction simulation. The data were processed in three modes: GPS-only, GLONASS-only and hybrid GNSS (GPS+GLONASS) using three different elevation cut-off angles. Accuracy analyses were carried out on the basis of final, daily EPN solutions at the observation time.
The International GNSS Service (IGS) provides high-accuracy clock products for both GNSS satellites and stations. On board of each GNSS satellite are located 3–4 atomic oscillators. In the case of ...CORS oscillators, the majority of them are equipped with internal oscillators and a part uses external, high-rate clocks. In the IGS network there are four types of external oscillators: quartz, rubidium, caesium and H-maser. These CORS are often reference stations for precise GNSS measurements or for time transfer. In this paper the author provides analyses of the internal and external stability of the reference stations oscillators via the usage of Allan variations. The results show a strong advantage of the external clocks over internal ones by about five orders of magnitude.
Millimetre-precise GNSS measurements may only be achieved by static relative (differential) positioning using a double-frequency receiver. This accuracy level is needed to address certain surveying ...and civil engineering issues. Relative measurements are performed using a single- or multi-network reference station, whose accuracy depends on a number of factors, such as the distance to the reference station, the session duration, the number of visible satellites, or ephemeris and clock errors. In this work, the author analyses the accuracy of static GNSS measurements according to the number of visible satellites, based on different minimal elevation cut-off angles. Each session was divided into three modes: GPS, GLONASS and hybrid GNSS (GPS+GLONASS). The final results were compared with the corresponding daily EPN solution at the observational epoch in order to determine their accuracy.
A Study of Outliers in GNSS Clock Products Maciuk, Kamil; Varna, Inese; Krzykowska-Piotrowska, Karolina
Sensors (Basel, Switzerland),
2024-Jan-25, Letnik:
24, Številka:
3
Journal Article
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Time is an extremely important element in the field of GNSS positioning. In precise positioning with a single-centimetre accuracy, satellite clock corrections are used. In this article, the longest ...available data set of satellite clock corrections of four GNSS systems from 2014 to 2021 was analysed. This study covers the determination of the quality (outliers number and magnitude), availability, stability, and determination of the specificity and nature of the clock correction for each satellite system. One problem with the two newest satellite systems (Galileo and BeiDou) is the lack of availability of satellite signals in the early years of the analysis. These data were available only in the later years of the period covered by the analysis, as most of the satellites have only been in orbit since 2018-2019. Interestingly, the percentage of outlying observations was highest in Galileo and lowest in BeiDou. Phase and frequency plots showed a significant number of outlying observations. On the other hand, after eliminating outlying observations, each system showed a characteristic graph waveform. The most consistent and stable satellite clock corrections are provided by the GPS and GLONASS systems. The main problems discussed in this paper are the determination of the number and magnitude of outliers in clock products of four GNSS systems (GPS, GLONASS, Galileo, Beidou) and the study on the long-term stability of GNSS clocks analysis, which covers the years 2014-2021.
This research is focused on searching for frequency and noise characteristics for available GNSS (Global Navigation Satellite Systems). The authors illustrated frequency stability and noise ...characteristics for a selected set of data from four different GNSS systems. For this purpose, 30-s-interval clock corrections were used for the GPS weeks 1982-2034 (the entirety of 2018). Firstly, phase data (raw clock corrections) were preprocessed for shifts and removal of outliers; GLONASS and GPS satellites characterize a smaller number of outliers than BeiDou and Galileo clock products. Secondly, frequency and Hadamard deviation were calculated. This study concludes that the stability of GPS and Galileo is better than that of BDS (BeiDou Navigation Satellite System) and GLONASS. Regarding noise, the GPS, Galileo, and BDS clocks are affected by the random walk modulation noise (RWFM), flashing frequency modulation noise (FFM), and white frequency modulation noise (WFM), whereas the GLONASS clocks are mainly affected only by WFM.
The idea to verify the height of the highest peaks (summits) in the Crown of Polish Mountains arose after analyzing sources regarding the date and method of measuring the height of these mountain ...peaks. Our investigations revealed that this type of material is not usually available, and the first mention of height values is most often noted in the inter-war period, and occasionally before WWI (when Poland did not exist as an independent state); most of these values are still in use to this day. The problem of accurate measurement of the height of mountain peaks concerns not only the peaks analyzed by the authors, but also almost all mountain peaks worldwide. Therefore, as part of this work, several trips were organized to the highest peaks of several dozen mountain ranges in the territory of Poland. Measurement was made using a precise geodetic GNSS receiver an accuracy of within 10 cm and a DTM model based on ALS (airborne laser scanning). The results showed that commonly published heights can differ by up to several meters from the actual ones. The most important element of this work consists of the establishment of new measurements of the heights of the highest peaks of all mountain ranges in Poland, which may result in an alteration of the officially recorded heights based on this article. Apart from verification of these heights, this work also aimed to address the issue of the heights of all characteristic objects whose heights must be verified by using modern satellite techniques.
The development of navigation satellite systems allows them to be used in many areas of trade, services and industry. This development is strongly visible in industries related to logistics and ...transportation where car navigation is becoming a standard for all kinds of vehicles. In this paper the author discusses navigation satellite systems, the principle of their operation and presents analysis of possible applications in businesses related to logistics and transport.
Several types of methods can solve equations of satellite motion numerically. These methods are divided into single and multi-step methods. The accuracy of each method depends directly on adopted ...integration step size between successive iterations. To achieve result with required accuracy it is important to maintain appropriate size of integration step. Inappropriate step size could cause local errors between iterations greater than accuracy of the method. Therefore, integration step size needs to be reduced until it does not affect accuracy of the final solution. Group of Runge-Kutta (RK) methods for solving equations of satellite motion have been analysed in this article. Five different methods: Runge Kutta 4th order, Runge Kutta 5th order and Runge Kutta Fehlberg 4th and 5th order methods were discussed. Compared to the classical Runge-Kutta integration method other methods are slower, but give results that are slightly more accurate.
Precise data processing from the Global Navigation Satellite Systems (GNSS) reference station network is mainly based on a combination of double-differenced carrier phase and code observations. This ...approach allows most of the measurement errors to be removed or reduced and is characterized as the most accurate method. However, creating observation differences between two receivers and two satellites increases the measurement noise of the observations by a factor of 2. As a result, it increases the impact of the incorrect definition of the noise characteristic on the results of the estimation of the unknowns in the positioning model. This is especially important in Multi-GNSS solutions, which integrate measurements from different systems, for which the stochastic parameters of observation may differ significantly. In this paper, the authors prepared a complex analysis of the noise type in double-differenced GNSS (GPS, GLONASS and Galileo) observations, both carrier phase and code ones, with a 1 s sampling interval. The Autocorrelation Function (ACF) method, the Lomb–Scargle (L-S) periodogram method, and the Allan variance (AVAR) method were used. The results that were obtained for the weekly set of measurement data showed that, depending on the system and type of observation, the noise level and its type are significantly different. Among the code measurements, the lowest noise levels were obtained for the GPS C5Q and Galileo C7Q/C8Q observations, with the standard deviations not exceeding ±10 cm, while the noisiest observations were for the GLONASS C1C and C2C signals, which had standard deviations of about ±90 cm and ±45 cm, respectively. For the carrier phase observations, each signal type was characterized by very similar noise levels of ±1.5–3.5 mm. The ACF analysis showed that 1 Hz double-differenced GNSS data can only be treated as being not correlated to time for carrier phase observations; for code observations, an irrelevant autocorrelation may be considered for measurement intervals greater than 20 s. Depending on the GNSS signals, the spectral index k varies in a range from −1.3 to −0.2 for code data and k = 0.0 in the case of phase data. Using the modified Allan deviation (MDEV) allows for specific noise types for each signal and GNSS system to be determined. All of the code observations were characterized by either flicker PM or white PM. In the case of the phase observations, they were all uniquely characterized by white PM (GPS and Galileo or by white PM and flicker PM (GLONASS).
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