Station Height Research Articles

Simulating the Performance of 6G Networks in Urban and Rural Scenarios by using NYUSIM 4.1

NYUSIM 4.0 is an advanced wireless channel simulator that models the behavior of radio waves in diverse environments, including urban and rural scenarios. This study explores the influence of factors such as buildings, vegetation, and human obstructions on the propagation of wireless signals. It analyzes how these factors affect the quality of service during signal propagation to better understand the performance of 6G networks in these environments. Simulations in NYUSIM 4.0 for Urban Microcell (UMi) and Rural Macro (RMa) scenarios provide essential insights for optimizing 6G networks. Simulation parameters include indices specific to channel parameters, antenna properties, spatial consistency parameters, and human obstructions. Directional power delay profile graphs highlight the variability of signal strength over time and distance, reflecting the complexity of signal path interactions. In the RMa scenario, intended for rural areas, the parameters include a frequency of 150 GHz, a base station height of 35 meters, and distances ranging from 10 to 1000 meters. The 3D graph of directional power versus delay illustrates power variability over time and distance, providing a visual representation of these performance metrics. The findings emphasize the impact of signal path diversity in urban and rural scenarios for 6G networks, highlighting the importance of parameters such as frequency and distance on communication system performance. This is crucial for ensuring optimal performance. The study provides a solid foundation for optimizing 6G networks through detailed modeling of different propagation scenarios.

Retrieval of refractivity fields from GNSS tropospheric delays: theoretical and data-based evaluation of collocation methods and comparisons with GNSS tomography

This paper focuses on the retrieval of refractivity fields from GNSS measurements by means of least-squares collocation. Collocation adjustment estimates parameters that relate delays and refractivity without relying on a grid. It contains functional and stochastic models that define the characteristics of the retrieved refractivity fields. This work aims at emphasizing the capabilities and limitations of the collocation method in modeling refractivity and to present it as a valuable alternative to GNSS tomography. Initially, we analyze the stochastic models in collocation and compare the theoretical errors of collocation with those of tomography. We emphasize the low variability of collocation formal variances/covariances compared to tomography and its lower dependence on a-priori fields. Then, based on real and simulated data, we investigate the importance of station resolution and station heights for collocation. Increasing the network resolution, for example, from 10 to 2 km, results in improved a-posteriori statistics, including a 10% reduction in the error statistic for the retrieved refractivity up to 6 km. In addition, using additional stations at higher altitudes has an impact on the retrieved refractivity fields of about 1 ppm in terms of standard deviation up to 6 km, and a bias reduction of more than 3 ppm up to 3 km. Furthermore, we compare refractivity fields retrieved through tomography and collocation, where data of the COSMO weather model are utilized in a closed-loop validation mode to simulate tropospheric delays and validate the retrieved profiles. While tomography estimates are less biased, collocation captures relative changes in refractivity more effectively among the voxels within one height level. Finally, we apply tomography and collocation to test their capabilities to detect an approaching weather front. Both methods can sense the weather front, but their atmospheric structures appear more similar when the GNSS network has a well-distributed height coverage.

The relationship between indoor airborne culturable bacteria with passenger flow in 132 traffic stations during 2019–2020, China

This study aims to provide technical support for the development of a rational administration strategy for indoor environment and passenger flow of stations. The analysis was conducted monitor data of long distance bus stations and train/high speed railway stations from the National project. The monitor and surveyed data included indoor airborne culturable bacteria (IAB), passenger flow, area and height of stations. Data analysis involved the use of paired non-parametric tests, correlation analysis, and mixed linear regression methods. A total of 132 pairs of stations were examined in this study. Additionally, significant variations were observed in the monitoring results for the IAB and passenger flow between 2019 and 2020 (p < 0.05). Specifically, the median values of these two factors in 2020 decreased by 50.52% and 48.33%, respectively, compared to 2019. (p < 0.05). A positive relationship between the daily average passenger flow and the IAB in long distance bus stations and train stations, particularly pronounced with medium sized waiting rooms, which located in subtropical cities with a general level of economic development. The mixed effect regression analysis revealed a significant association between passenger flow (OR = 1.564, 1.288–1.898), per capita volume (OR = 0.856, 0.733–0.998), and per capita area (OR = 0.806, 0.678–0.956) with the IAB (p < 0.05) just in long distance bus stations. It is crucial to regulate passenger flow and per capita area in the waiting room of long distance bus stations to mitigate the spread of airborne culturable bacteria during infectious disease epidemics.

Precise Geoid Determination in the Eastern Swiss Alps Using Geodetic Astronomy and GNSS/Leveling Methods.

Astrogeodetic deflections of the vertical (DoVs) are close indicators of the slope of the geoid. Thus, DoVs observed along horizontal profiles may be integrated to create geoid undulation profiles. In this study, we collected DoV data in the Eastern Swiss Alps using a Swiss Digital Zenith Camera, the COmpact DIgital Astrometric Camera (CODIAC), and two total station-based QDaedalus systems. In the mountainous terrain of the Eastern Swiss Alps, the geoid profile was established at 15 benchmarks over a two-week period in June 2021. The elevation along the profile ranges from 1185 to 1800 m, with benchmark spacing ranging from 0.55 km to 2.10 km. The DoV, gravity, GNSS, and levelling measurements were conducted on these 15 benchmarks. The collected gravity data were primarily used for corrections of the DoV-based geoid profiles, accounting for variations in station height and the geoid-quasigeoid separation. The GNSS/levelling and DoV data were both used to compute geoid heights. These geoid heights are compared with the Swiss Geoid Model 2004 (CHGeo2004) and two global gravity field models (EGM2008 and XGM2019e). Our study demonstrates that absolute geoid heights derived from GNSS/leveling data achieve centimeter-level accuracy, underscoring the precision of this method. Comparisons with CHGeo2004 predictions reveal a strong correlation, closely aligning with both GNSS/leveling and DoV-derived results. Additionally, the differential geoid height analysis highlights localized variations in the geoid surface, further validating the robustness of CHGeo2004 in capturing fine-scale geoid heights. These findings confirm the reliability of both absolute and differential geoid height calculations for precise geoid modeling in complex mountainous terrains.

Research on Train-Induced Vibration of High-Speed Railway Station with Different Structural Forms.

Elevated stations are integral components of urban rail transit systems, significantly impacting passengers' travel experience and the operational efficiency of the transportation system. However, current elevated station designs often do not sufficiently consider the structural dynamic response under various operating conditions. This oversight can limit the operational efficiency of the stations and pose potential safety hazards. Addressing this issue, this study establishes a vehicle-bridge-station spatial coupling vibration simulation model utilizing the self-developed software GSAP V1.0, focusing on integrated station-bridge and combined station-bridge elevated station designs. The simulation results are meticulously compared with field data to ensure the fidelity of the model. Analyzing the dynamic response of the station in relation to train parameters reveals significant insights. Notably, under similar travel conditions, integrated stations exhibit lower vertical acceleration in the rail-bearing layer compared to combined stations, while the vertical acceleration patterns at the platform and hall layers demonstrate contrasting behaviors. At lower speeds, the vertical acceleration at the station concourse level is comparable for both station types, yet integrated stations exhibit notably higher platform-level acceleration. Conversely, under high-speed conditions, integrated stations show increased vertical acceleration at the platform and hall levels compared to combined stations, particularly under unloaded double-line working conditions, indicating a superior dynamic performance of combined stations in complex operational scenarios. However, challenges such as increased station height due to bridge box girder maintenance, track layer waterproofing, and track girder support maintenance exist for combined stations, warranting comprehensive evaluation for station selection. Further analysis of integrated station-bridge structures reveals that adjustments in the floor slab thickness at the rail-bearing and platform levels significantly reduce dynamic responses, whereas increasing the rail beam height notably diminishes displacement responses. Conversely, alterations in the waiting hall floor slab thickness and frame column cross-sections exhibit a minimal impact on the station dynamics. Overall, optimizing structural dimensions can effectively mitigate dynamic responses, offering valuable insights for station design and operation.

Data traffic unloading method of internet of things based on mobile edge computing

The Industrial Internet of Things integrates modern technologies such as intelligent terminals, computer technology, and big data, achieving low cost and high applicability in industrial production processes, and improving industrial production efficiency. The offloading of IoT data traffic requires significant energy consumption due to limited mobile terminal device resources. For this reason, the author designs a method of IoT data traffic unloading based on mobile edge computing. The initialization simulation parameters include the number of mobile users, the number of base stations equipped with edge servers, fixed bandwidth, base station height, etc. Calculate the distance and channel power gain from each base station to mobile users, and optimize power allocation through algorithms such as simulated annealing and PSO. The binary PSO algorithm is used to maximize the welfare in edge computing. Finally, by comparing with local offloading, utilizing layered offloading methods, and collaborative computing offloading methods based on fiber wireless networks. Simulation resultsThe energy consumption of SAPA is generally higher than that of PSO, and with the increase of mobile users, the energy consumption of both algorithms shows a significant growth trend. Especially, SAPA's energy consumption is significantly higher than PSO when the number of users is 40 and 60. This indicates that in the mobile network environment, PSO algorithm has more advantages in energy consumption than SAPA, By using particle swarm optimization algorithm to further optimize energy consumption, it greatly saves energy consumption. In comparison to local execution, the proposed offloading method yields substantial energy savings of nearly 62.5 %. The maximum difference in energy consumption between the proposed method and the collaborative computing offloading method based on fiber optic wireless networks is 268 J, while the maximum difference compared to the layered offloading method is 150 J. These results highlight the strategy's ability to enhance the computational efficiency of high-priority tasks on edge servers, concurrently reducing latency and energy consumption for task completion. This underscores the effectiveness of the proposed offloading method in conserving energy and emphasizes its practical significance.

Evaluating the Positional Stability Status of the Druk Corsnet: A Preliminary Study

Abstract— The continuously operating reference station (CORS) that provides a Global Navigation Satellite System (GNSS) enables precise location and height data for various applications such as site selection of important engineering projects and constructions and hazard analysis. Similarly, the most common applications of the CORS network, in Bhutan, are for engineering, cadastral, geodetic, and topographical surveys. In this regard, the consistency and dependability of the data from the CORS station are crucial. Moreover, the ability of such applications heavily depends on precise and reliable data from the CORS network. However, Bhutan has not conducted any studies on the stability, in terms of its position, and height fluctuation of the CORS station. Therefore, the goal of this study is to determine the positional and height variation of the 9 CORS stations that are operational in Bhutan between the years 2016 to 2022. Assessing the stability and dynamic behavior of reference stations in a CORS network is part of position variation analysis. It is feasible to identify and quantify a variety of geodetic occurrences by examining the time series of positional analysis. Analysis of height variation focuses on changes in orthometric heights throughout the CORS network. In our study, all the available GNSS CORS data are processed and the displacement in height and position is computed and compared. The analysis consists of a simple method (mean value subtraction) of time series data, which is computed and compared. The major findings show that the absolute mean standard deviation in the position of the stations was 5.49 cm, 6.36 cm, and 4.24 cm vertical (height), ease, and north horizontal component respectively. The findings highlight that the proposed method of determining the variation in height and location of the CORS stations is fairly practical and will help the user community to guide them in using the CORS network across Bhutan wisely. Similarly, the result of this study will be a relevant source of information to organizations such as the National Land Commission Secretariat (NLCS) as a means to augment the system in the future.

THE EFFECT OF SEASONAL VARIATION ON GNSS ZENITH TROPOSPHERIC DELAY

Abstract. The Global Navigation Satellite System (GNSS) signal experiences delays caused by the atmosphere, leading to the lengthening of the geometric path of the ray, commonly referred to as tropospheric delay. This delay is a significant source of error in GNSS positioning, contributing to a bias in the height component of several centimeters, even when meteorological data are simultaneously recorded and used in tropospheric models. In this study, considering seasonal variations, we investigated the impact of tropospheric delay on the GNSS height component. GNSS stations, part of the Turkish RTK CORS Network known as TUSAGA-Active (Turkish National Permanent GNSS Network Active), covered different heights over the 2014–2019 period. Daily coordinates of GNSS stations and tropospheric zenith delay were obtained through the GAMIT/GLOBK software solution.In the study, temperature, pressure, and relative humidity data of meteorological stations at different heights were converted to mean sea level. By using these values, interpolation estimates were made for the continuous GNSS stations in the same region with the IDW method. The most significant delay in GNSS signals occurs in July and August. This effect, which causes periodic changes in the zenith delay, varies inversely with the station's height. With the increase in the amount of water vapor in the atmosphere in parallel with the rise in the temperature in the summer months, it is seen that the stations at a low height are more exposed to the tropospheric effect than the stations at higher heights. In addition, GNSS stations' reduced meteorological values (temperature, pressure and relative humidity) show that the zenith delay values changed directly proportional to the temperature and inversely proportional to the pressure and relative humidity.

Structural Stability and Weak Points Mechanism of a High and Vertical Enclosed Isolated Phase Bus

Recently, with the rapid rise of new energy generation, pumped storage power stations also have experienced rapid development. Due to the considerable vertical height of these power stations, high and vertical enclosed isolated phase buses (EIPB) are more and more widely used. This type of high and vertical EIPB structure differs from the horizontal EIPB structure, as it is more significantly influenced by the gravitational load during actual operation. Thus, it is crucial to investigate the stability of the novel high and vertical EIPB structure under its own gravity load. In this study, the strength of the I-beam and cross-arm of the EIPB under the influence of the gravitational load was studied through analytical calculations and finite element static analysis. The results indicate that the strength of the I-beam and cross-arm is within the threshold of the corresponding material’s load-bearing capacity, demonstrating the stability of the EIPB structure. This work holds significant value for the structural design and further optimization of high and vertical EIPB.

Analyzing the Effect of Base Station Height on the NYUSIM Model and Investigation of Received Signal Power for 6G Wireless Communications

Analyzing the Effect of Base Station Height on the NYUSIM Model and Investigation of Received Signal Power for 6G Wireless Communications

The effect of data sources on calculating mean temperature and integrated water vapor in Iran

AbstractThe weighted mean temperature () plays a crucial role in calculating Precipitable Water Vapor (PWV) and integrated water vapor (IWV) using Global Navigation Satellite Systems (GNSS) techniques. Currently, the primary sources for meteorological parameters are radiosonde measurements and Numerical Weather Models (NWMs). This study focuses on assessing the influence of different data sources on the computation of and IWV in Iran. The investigation involved comparing several datasets: ERA5 numerical data with spatial resolutions of 0.125° and 2.5° (ERA5 0.125, ERA5 2.5), ERA‐Interim, NCEP numerical data and results derived from the GPT3 model. Validation of the results utilized data from 12 radiosonde stations situated across Iran. In addition, the precision of the IWV parameter was evaluated by utilizing measurements from the only available IGS station in the region, situated in Tehran. The results revealed that ERA5 0.125 exhibited superior accuracy in estimation compared with the other datasets, showing a discrepancy of approximately 1–2 K. In contrast, the GPT3 model displayed an accuracy of about 3 K. Analysing the results across different months of the year revealed elevated root mean square error (RMSE) values during warmer months, with little variability based on station height in the region for the four datasets. Regarding IWV, the ERA5 0.125 dataset outperformed the other three datasets, demonstrating an accuracy of about 0.07 kg m−2. Notably, RMSE values during summer were approximately 50% higher compared with the annual RMSE.

Interference Analysis Between 5G System and Fixed Satellite Service in the 28 GHz Band

One of the most favorable frequency bands for 5G technology is the 27.5 - 28.5 GHz band which has been used by Fixed Satellite System (FSS) service in the uplink direction. This potentially causes interference between the two systems. This study aims to analyze the interference that occurs between satellite earth stations and 5G access points (AP), and between 5G AP and satellite sky stations. The analysis is carried out based on simulations using the Spectrum Engineering Advanced Monte Carlo Analysis Tool (SEAMCAT) software, with two scenarios. The first scenario is to analyze interference between the 5G AP and the FSS sky station. With the C/I interference criterion of 40.2 dB, the simulation results show that the 5G AP will not interfere with the FSS sky station. The second scenario is the interference simulation between FSS earth station and 5G AP. The simulation is carried out by varying the distance between the earth station and the 5G AP, the height of the earth station, and the height of the 5G AP. Based on the simulations, it is shown that the FSS earth station can interfere with 5G AP with a probability of up to 60%, so it is necessary to adjust the distance between systems and the height of the antenna to minimize the interference. The shortest distance needed to minimize interference is 36 km with an earth station height of 5 meters.

On the importance of accurate pole and station coordinates for VLBI Intensive baselines

Very long baseline interferometry (VLBI) is a geodetic technique capable of deriving the complete set of Earth orientation parameters, including the highly variable Earth’s phase of rotation. This observable can be expressed through UT1–UTC, the difference between the Universal Time and the Coordinated Universal Time. The so-called Intensive sessions, or Intensives, are typically 1-h sessions between two to three stations that are observed daily with the primary goal of determining UT1–UTC with a short latency. In this publication, we examine the impact of erroneous a priori information on the UT1–UTC estimation with VLBI Intensive sessions in a systematic way and on a global scale. Our findings are based on a simulation study which is carried out on a regular 10 times 10 degree grid of artificial telescopes. In the simulations, realistic errors are introduced in the station coordinates, polar motion and nutation to get a global picture of the impact of these errors on the estimation of UT1–UTC. Our results reveal that in contrast to errors in the horizontal components of the station coordinates, an error in the station height only slightly affects the UT1–UTC estimate. North–south-oriented baselines are in general strongly affected by errors in the a priori information. In all cases, very short and very long baselines as well as baselines with a midpoint close to the equatorial plane are less robust. On the other hand, east–west-oriented baselines, except equatorial baselines, seem to be rather resistant against errors of these a priori values.

Preliminary inquiry on the linear relationship between the height of the station and the ground height error retrieved by GNSS-IR with low-cost smart electronic equipment

Global Navigation Satellite System Interferometric Reflectometry (GNSS-IR) ground height retrieval technology is based on global navigation satellite system (GNSS) signal reflection, which can achieve efficient and high-precision ground retrieval. However, errors cannot be avoided. And whether there is a linear relationship between the height of the station and the error is unknown. This research uses Hi-Target geodetic GNSS receivers, smart phone devices (Honor 60) and smart tablet devices (Huawei MatePad Pro) to collect a total of 5 d data from DOY65 to DOY69 in 2023, with the station heights of 0.8 m, 1.0 m, 1.2 m, 1.4 m and 1.6 m, respectively. The experimental results show that each satellite can effectively establish a linear relationship between the inversion error and the station height, which can be used in the error compensation research of different station heights under the limitation that the height of reflector is between 0.8 m and 1.6 m. Simultaneously, the error is related to the influence of comprehensive factors such as reflector type, satellite number, and data-receiving equipment. Secondly, two clustering methods, k-means and k-media, are introduced to cluster a and b in the linear relationship y = ax + b of each satellite, and it is proved that the linear relationship between inversion error and station height is obviously related to ground reflection surface (plastic track and concrete ground). Finally, it is verified that the height measurement accuracy of low-cost smart electronic equipment (Root Mean Square Error (RMSE): 0.047 m and 0.042 m) is worse than that of GNSS (RMSE: 0.010 m), but it still has good measurement performance. All in all, this study provides an essential technical reference for the error compensation of different station heights and for the application of GNSS-IR with low-cost smart electronic equipment. Due to its low-cost advantage, it has great potential in developing other surface parameter inversion of GNSS-IR technology.

A Comparison of Different Station Data on Revealing the Characteristics of Extreme Hourly Precipitation Over Complex Terrain: The Case of Zhejiang, China

AbstractBoth long‐term but small number of national stations and short‐term but large number of regional stations have been frequently used to study the extreme hourly precipitation (EXHP) in China. However, few studies focus on the differences of the two for revealing the features of EXHP. In this study, the characteristics of EXHP in Zhejiang Province are investigated using three rainfall data sets at three threshold criteria. The comparison between different data sets shows that increasing the station density can better reflect the climatic spatial distribution of EXHP thresholds if long‐term data is absent. The majority of EXHP can be classified into four weather types: the southwesterly wind type (30.7%–48.5%), the trough type (12.2%–23.6%), the tropical cyclone (TC) type (11.4%–17.5%) and the easterly wind type (4.9%–17.9%). The selection of stations is more sensitive to the proportions of the four weather types than the statistical years and threshold criteria. The monthly and diurnal variations of EXHP, as well as their differences revealed by the three data sets, are varied by weather type. Only using national stations cannot distinguish the spatial differences between the TC type and the easterly wind type, and there is an underestimation for southwesterly wind type and trough type in the mountainous area of southwest Zhejiang. The statistical year and station height are the main reasons for the differences in the duration of EXHP events calculated by different data sets, with the TC type having the largest effect and the southwesterly wind type the smallest.

Positioning Optimization of UAV (Drones) Base Station in Communication Networks

Unmanned aerial vehicles (UAV) and cellular networks are growing closer to being integrated in the realm of wireless communications, which will improve service quality even further. In this study, we investigate a wireless communication system in which two types of base stations—in the air and on the ground—serve separate groups of users. We analyze the effect of the aerial base station (ABS) height and transmit power on the system's downlink and uplink data rates while accounting for the reciprocal interference between the Aerial and terrestrial communication lines. The findings demonstrate that in many cases the best ABS altitude and transmit Power are either the highest or lowest values attainable. The distance between the ABS, the ABS user (AU), and the terrestrial base station user, among other factors, may affect how well they all communicate (TU). In this article we will discuss the following topics: unmanned aerial vehicle (UAV), terrestrial base station (BTS), transmit power optimization (TPO), interference (I), downlink (DL), and uplink (UL).

수소충전소 설비운영 안전관리 상용화를 위한 CBM+활용 방안 연구

Purpose: This study aims to meet the functional safety requirements using condition-based maintenance plus (CBM+) to ensure the safe operation of equipment, such as chillers, compressors, and dispensers, used in hydrogen refueling facilities. BRMethods: For the commercialization of the safety management of hydrogen refueling stations, we demonstrate an approach for detecting equipment abnormalities during operation by measuring sound, vibration, and current. CBM+ is used for fault diagnosis; the results are compared with those of the traditional fault diagnosis methods.BRResults: At hydrogen refueling stations in South Korea, 90.48% of accidents occurred due to hydrogen leakage from 2005 to 2014. During the same period, 7 (31.82%) out of 22 such accidents were caused by human errors in the United States. Through structural analysis of vertical axis, lateral sides, and height of the hydrogen charging stations, we propose a method that uses sensor nodes, sensor systems, and communication systems for CBM+.BRConclusion: Only a few empirical studies have reported the use of CBM+ for hydrogen refueling stations in South Korea. Effective strategies for CBM+ have also not been presented. Through technical research and institutional improvement, including this study, it is necessary to secure functional safety and PHM technology for CBM for the safe operation of hydrogen refueling stations in South Korea. In addition, data based on several factors, including the equipment component type, failure, and safety risk level, must be acquired in a standard format. However, to eliminate the safety risks of hydrogen refueling stations, hydrogen leakage accidents must be primarily avoided.

Regional modeling and forecasting of precipitable water vapor using least square support vector regression

We propose a new model for spatio-temporal modeling and forecasting of precipitable water vapor (PWV) using least square support vector regression (LS-SVR) method. The LS-SVR uses simple linear equations. As a result, the complexity of the computational algorithm is reduced. In addition, the convergence speed and accuracy of the results increase. The evaluation of the new method has been done with the observations of the GPS networks at north-west and central Alborz in Iran. In the north-west GPS network, observations of 23 GPS stations in the period of 27 October to 10 November 2011 are used. However, in central Alborz network, the observations of 11 GPS stations in the period of 10 to 24 June 2016 have been used. The north-west GPS network is in the mountainous region and its observations are for the winter season. But, the second network is near the coastal area and summer season measurements are used. The latitude, longitude and height of GPS stations, DOY, time, relative humidity, temperature and pressure are considered as an input of the LS-SVR model. The output of the new model is the PWV (LS-SVRPWV). After the training step, the new model is used to estimate the spatio-temporal variation of PWV. The results of the LS-SVR model are compared and evaluated with the standard neural network (SNN), adaptive neuro-fuzzy inference system (ANFIS), support vector regression (SVR), Saastamoinen, global pressure and temperature 3 (GPT3), voxel-based tomography (VBT) models, as well as with radiosonde measurements. Error evaluation of models has been done in control stations as well as by precise point positioning (PPP) method. For LS-SVR model, the averaged RMSE in the control stations of the north-west GPS network is 1.69 mm, while for the central Alborz GPS network, 1.88 mm is calculated. Also, the averaged relative error of LS-SVR model calculated in the Tabriz and Tehran radiosonde stations are 4.66 % and 6.12 %, respectively. The results of this paper show that the LS-SVR model has a very high capability in forecasting the spatio-temporal variation of PWV at the GPS network territory. The new model can be used for accurate estimation of PWV, meteorological applications and flood forecasting.

On the relation of GNSS phase center offsets and the terrestrial reference frame scale: a semi-analytical analysis

Phase center offsets (PCOs) of global navigation satellites systems (GNSS) transmit antennas along the boresight axis introduce line-of-sight-dependent range changes in the modeling of GNSS observations that are strongly correlated with the estimated station heights. As a consequence, changes in the adopted PCOs impact the scale of GNSS-based realizations of the terrestrial reference frame (TRF). Vice versa, changes in the adopted TRF scale require corrections to the GNSS transmit antenna PCOs for consistent observation modeling. Early studies have determined an approximate value of alpha =-0.050 for the ratio of station height changes and satellite PCO changes in GPS orbit determination and phase center adjustment. However, this is mainly an empirical value and limited information is available on the actual PCO-scale relation and how it is influenced by other factors. In view of the recurring need to adjust the IGS antenna models to new ITRF scales, a semi-analytical model is developed to determine values of alpha for the four current GNSSs from first principles without a need for actual network data processing. Given the close coupling of satellite boresight angle and station zenith angle, satellite PCO changes are essentially compensated by a combination of station height, zenith troposphere delay, and receiver clock offset. As such, the value of alpha depends not only on the orbital altitude of the considered GNSS but also on the elevation-dependent distribution of GNSS observations and their weighting, as well as the elevation mask angle and the tropospheric mapping function. Based on the model, representative values of alpha _text {GPS}=-0.051, alpha _text {GLO}=-0.055, alpha _text {GAL}=-0.041, and alpha _text {BDS-3}=-0.046 are derived for GPS, GLONASS, Galileo, and BeiDou-3 at a 10^circ elevation cutoff angle. These values may vary by varDelta alpha approx 0.003 depending on the specific model assumptions and data processing parameters in a precise orbit determination or precise point positioning. Likewise changes of about pm 0.003 can be observed when varying the cutoff angle between 5^circ and 15^circ .

A Height Nonlinear Velocity Field Algorithm for CORS Station Based on GARCH Model.

In this study, the basic concept of height nonlinear velocity field modeling in the CORS station is described. The noise results in a large deviation between the observation and predicted height. An ARCH testing method for heteroscedasticity of CORS height residual square series was proposed and the non-stationary characteristic of CORS height residual square time series was proved. A CORS height nonlinear velocity field reconstruction method based on the GARCH model was proposed. First, a nonlinear LS periodic fitting model was established for CORS height series data. Then, a GARCH model was established for the fitted non-stationary residual series. Finally, the signal term, linear trend term, and GARCH model noise term of nonlinear LS modeling were combined to reconstruct the nonlinear velocity field of the CORS height. The RMSE of nonlinear LS cycle modeling for 25 CORS stations worldwide ranged from 5 to 10 mm. The differences between the velocity, approximate annual and semi-annual amplitudes, and SOPAC results were 0.73 mm/a, 0.94 mm, and 0.51 mm, respectively. Compared with the centimeter amplitude of the CORS station height, the accuracy of the nonlinear model established in this study met the requirements. The results of height nonlinear velocity field reconstruction at 25 CORS stations worldwide showed that the mean square error of prediction of the one-year height movement reached 9 mm, and the average prediction accuracy of the semi-annual was 7 mm. Compared with the calculation accuracy of the current global CORS elevation component of 3–5 mm, the prediction error in this study was about 3 mm. The expected goal was achieved regarding the accuracy of the CORS station height nonlinear velocity field model.