Jesus René Vázquez-Ontiveros

Geomagnetic storms can severely disturb the ionosphere, degrading Global Navigation Satellite System (GNSS) performance, particularly at low latitudes. The 10 May 2024 superstorm produced a strong ionospheric response across Mexico, with well-defined positive and negative phases observed at all analyzed stations. The proximity in time of %dTEC peaks to the second and third steps of the storm’s main phase, together with their local time dependence, indicates that Prompt Penetration Electric Fields (PPEFs) dominated the initial positive phase on the dayside. These eastward electric fields uplifted the F-region plasma, enhancing TEC values—especially at northern stations, where increases reached ±180%. In contrast, the subsequent nighttime depletion and extended recovery were mainly driven by composition-related plasma loss and enhanced recombination. A suppression of TEC followed the positive phase, with depletions between −58% and −77%, showing a persistent latitudinal gradient. Low-cost GNSS receivers successfully captured these ionospheric signatures but exhibited higher positioning degradation—up to 50% greater than geodetic-grade receivers. Multi-constellation Precise Point Positioning (PPP) mitigated these effects, reducing 3D errors by up to 23% and 53% in geodetic and low-cost receivers, respectively. These findings reveal the day–night dependence of ionospheric storm phases and underscore the importance of regional multi-GNSS monitoring during extreme space weather.

It has been proven that precise point positioning (PPP) is a well-established technique to obtain high-precision positioning in the order between centimeters and millimeters. In this context, different studies have been carried out to evaluate the performance of PPP in static mode as a possible alternative to the relative method. However, only a few studies have evaluated the performance of a large number of different open-source software programs and have focused extensively on online free PPP services. Therefore, in this paper, a comprehensive comparison of processing in static mode between different open-source software and the online free PPP services is developed. For the evaluation, different GNSS observation files collected at 45 International GNSS Service (IGS) stations distributed worldwide were processed in static PPP mode. Within this frame of reference, ten open-source PPP software and five online free PPP services were studied. The results from the processing strategy demonstrate that it is possible to obtain precision in the order of millimeters with both open-source software and online PPP services. In addition, online PPP services experienced better performance than some other specialized PPP software. In summary, the results show that the daily solutions for the E (East), N (North), and U (Up) components estimated by the ten open-source software and by the five online free PPP services can reach millimeter precision for some stations. Among the open-source software, the PRIDE-PPPAR presented the best performance with a Root Mean Square Error (RMSE) of 5.52, 5.40, and 6.79 mm in the E, N, and U components, respectively. Alternatively, in the case of the online free PPP services, the APPS and CSRS-PPP produced the most accurate results, with RMSE values less than 12 mm for the three components. Finally, the open-source software and online free PPP services experienced similar positioning performance in the horizontal and vertical components, demonstrating that both can be implemented in static mode without compromising the accuracy of the measurement.

A positional accuracy obtained by the Precise Point Positioning and static relative methods was compared and analyzed. Test data was collected using low-cost GNSS receivers of single- and dual-frequency in urban areas. The data was analyzed for quality using the TEQC program to determine the degree of affectation of the signal in the urban area. Low-cost GNSS receivers were found to be sensitive to the multipath effect, which impacts positioning. The horizontal and vertical accuracy was evaluated with respect to Mexican regulations for the GNSS establishment criteria. Probable Error Circle (CEP) and Vertical Positioning Accuracy (EPV) were performed on low cost GNSS receiver observation data. The results show that low-cost dual-frequency GNSS receivers can be used in urban areas. The precision was obtained in the order of 0.013 m in the static relative method. The results obtained are comparable to a geodetic receiver in a geodetic baseline of <20 km. The study does not recommend using single and dual frequencies low cost GNSS receivers based on results obtained by the Precise Point Positioning (PPP) method in urban areas. The inclusion of the GGM10 model reduces the vertical precision obtained by using low cost GNSS receivers in both methods, conforming to the regulations only in the horizontal component.

Nowadays, with the incursion of low-cost GNSS receivers with modern characteristics, it is common to investigate and apply new methodologies and solutions with different receivers of this nature. Based on this fact, the performance of the solution obtained from the low-cost GNSS receiver is evaluated compared to a geodetic grade GNSS receiver at different sampling frequencies for the PPP-static and PPP-kinematic modes. For this, the original RINEX observation files were analyzed and decimated into different sampling rates as 0.1, 0.2, 1, 5, 15 and 30 s with TEQC software. All RINEX files were submitted to the Canadian Spatial Reference System Precise Point Positioning (CSRS-PPP) online service for processing with static and kinematic modes. The PPP-derived coordinates from the low-cost GNSS receiver were compared with the geodetic receiver to evaluate the obtained solution. The results reveal that the behavior of all studied sampling rates from the low-cost GNSS receiver are constant in achieved positioning. In addition, the achieved precision shows that it is recommendable to use a high sampling rate to obtain a cm level in PPP-static mode by using a low-cost GNSS receiver, this mode being the most accurate and potential alternative for structural health monitoring studies, mapping and positioning in urban areas.

Global Positioning System (GPS) technology is reported in the literature as a reasonable alternative for the structural health monitoring (SHM) of bridges. However, more validations of GPS technology must be performed to extract the associated risk of bridges, particularly applying probabilistic concepts. This paper presents a probabilistic approach to evaluating the safety of bridges using real-time dynamic displacements obtained via geodetic-grade GPS receivers. The implementation of the probabilistic approach is demonstrated by the evaluation of the serviceability condition of a real-scale bridge. The structural evaluation involved the continuous extraction of GPS displacement data over the course of 1 h at three different periods of the day from Monday to Sunday. A comprehensive probabilistic study is developed based on dynamic displacements in terms of reliability index and probability of failure. Finally, based on the findings documented in this paper, the detection of unsafe serviceability conditions of bridges is possible by integrating GPS technology and the probabilistic approach presented in this research, which may help to inform decisions about the improvement or retrofit of bridge structures.