Nowadays, the high rate GNSS (Global Navigation Satellite Systems) positioning methods are widely used as a complementary tool to other geotechnical sensors, such as accelerometers, seismometers, and inertial measurement units (IMU), to evaluate dynamic displacement responses of engineering structures. However, the most common problem in structural health monitoring (SHM) using GNSS is the presence of surrounding structures that cause multipath errors in GNSS observations. Skyscrapers and high-rise buildings in metropolitan cities are generally close to each other, and long-span bridges have towers, main cable, and suspender cables. Therefore, multipath error in GNSS observations, which is typically added to the measurement noise, is inevitable while monitoring such flexible engineering structures. Unlike other errors like atmospheric errors, which are mostly reduced or modeled out, multipath errors are the largest remaining unmanaged error sources. The high noise levels of high-rate GNSS solutions limit their structural monitoring application for detecting load-induced semi-static and dynamic displacements. This study investigates the estimation of accurate dynamic characteristics (frequency and amplitude) of structural or seismic motions derived from multipath-affected high-rate GNSS observations. To this end, a novel hybrid model using both wavelet-based multiscale principal component analysis (MSPCA) and wavelet transform (MSPCAW) is designed to extract the amplitude and frequency of both GNSS relative- and PPP- (Precise Point Positioning) derived displacement motions. To evaluate the method, a shaking table with a GNSS receiver attached to it, collecting 10 Hz data, was set up close to a building. The table was used to generate various amplitudes and frequencies of harmonic motions. In addition, 50-Hz linear variable differential transformer (LVDT) observations were collected to verify the MSMPCAW model by comparing their results. The results showed that the MSPCAW could be efficiently used to extract the dynamic characteristics of noisy dynamic movements under seismic loads. Furthermore, the dynamic behavior of seismic motions can be extracted accurately using GNSS-PPP, and its dominant frequency equals that extracted by LVDT and relative GNSS positioning method. Its accuracy in determining the amplitude approaches 91.5% relative to the LVDT observations.

Skyscrapers cause both limited sky-view and multipath error when using Global Navigation Satellite System (GNSS) measurements for monitoring structural movements. To reduce multipath errors, cut-off elevation angle can be set to a high value such as 30°−40°. However, in the case of employing high cut-off elevation angles, the use of GPS only may not provide adequate positioning solutions. To overcome this problem, Galileo and GLONASS observations are combined with GPS observations. This study experimentally investigates the contribution of multi-GNSS for studying the effects of different cut-off elevation angles on the accuracy of high-rate GNSS results for detecting characteristics of dynamic motions for structural health monitoring (SHM). The filtration design, noise level and Signal-to-Noise Ratio (SNR) of high-rate GNSS measurements of GPS-only, GPS/Galileo, GPS/GLONASS and GPS/GLONASS/Galileo are assessed for different cut-off elevation angles. The results demonstrate that the SNR of GNSS solutions for GPS/GLONASS and GPS/GLONASS/Galileo is the highest, which signifies their use in SHM. The accuracy of the dynamic movements of structures can be attained to 2 mm, on average, using multi-GNSS measurements even when using high cut-off elevation angles up to 40°. The precision of GPS/GLONASS and GPS/GLONASS/Galileo systems with different cut-off elevation angles was high when referenced to LVDT.

This study presents the capability of the single-frequency (SF) variometric approach (VA) technique with low-cost GNSS observations to detect short-term dynamic behaviors. Harmonic oscillations with amplitudes between 5 and 20 mm and frequencies between 0.3 and 5.0 Hz were generated employing a single-axis shake table to investigate the performance of the SF-VA technique in the structural health monitoring (SHM) system. Besides, a Mw 6.9 Kobe, 1995 earthquake simulation was generated using the shake table to analyze the SF-VA performance for the earthquake early warning (EEW) system. A low-cost u-blox ZED-F9P GNSS receiver and ANN-MB-00 patch antenna were used to collect GNSS observations at a 20 Hz sampling rate during the experiments. The observations were processed using the MATLAB-based open-source PPPH-VA software in real-time (RT) mode, considering eight different satellite combinations. The capability of the SF-VA technique to detect horizontal dynamic behaviors in RT mode was investigated in the frequency and time domains, accepting the displacements from the linear variable differential transformer sensor as a reference. The results in the frequency domain demonstrate that the SF-VA technique with low-cost GNSS observations can successfully detect the peak frequency value of short-term harmonic oscillations up to 5 Hz. Moreover, time domain findings emphasize that the short-time dynamic oscillations can be determined with the SF-VA technique with an accuracy ranging from 0.8 to 6.4 mm. Earthquake simulation experiment results demonstrate that the strong ground motions caused by mega earthquakes can be determined at mm-level by the SF-VA method. The results of both experiments show that multi-GNSS observations contribute to the SF-VA technique considerably. Overall, the findings reveal that the SHM and EEW systems can be operated with low-cost GNSS receivers, and the natural frequency of the man-made structures and accurate displacement values of seismic waveforms can be determined in RT with the SF-VA technique.

In recent years, the continuously operating reference station – Turkey (CORS-TR) system has been widely used in engineering and cadastral work in Turkey due to ease of use, low cost, and national legislative requirements. In this study, long-term Network RTK (Real-time Kinematic) data were collected under 10°, 20°, 30° and 40° satellite views using a different approach from previous work. In order to evaluate the positioning performance of the system, the measurements were undertaken at different elevation angles (open, partially blocked and extremely blocked) and by considering three different correction techniques (FKP, VRS and MAC), and the results were evaluated in terms of repeatability. From the analysis of the data, it was understood that the performances of the three correction techniques were generally similar, and even in the case of a limited satellite view, the errors remained below 7 cm in all three techniques. However, when the 2D and 3D components were analyzed together, VRS technique showed better results than the other two techniques.