Subjects -> GEOGRAPHY (Total: 493 journals)
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 GPS SolutionsJournal Prestige (SJR): 1.674 Citation Impact (citeScore): 5Number of Followers: 28      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1521-1886 - ISSN (Online) 1080-5370 Published by Springer-Verlag  [2469 journals]
• Impact of clock drift on WiFi round-trip-time ranging and positioning

Abstract: Abstract Indoor high-precision positioning is currently one of the most interesting topics in the location-tracking and positioning research area. Although the WiFi round-trip-time (RTT) provides a promising ranging and positioning method, it faces two issues that need to be addressed. One is the ranging error drift, and the other is the ranging information loss. Existing research has mainly focused on the ranging error, and several solutions have been proposed. However, these solutions are mostly applied to the data level, and the cause of phase distortion error has not been found. The loss of ranging information has been simply attributed to the poor external environment. In this work, the impact of clock drift on WiFi RTT positioning is investigated and considered the root cause of the abovementioned issues. On this basis, a theory of the clock drift model is established and experimentally verified. This model can effectively explain the mechanism of the ranging error drift and the ranging information loss. Furthermore, the impact of the clock drift on missing positioning observations is investigated in three actual applicational situations, including the sampling rate, multipath effect, and power-saving mode. Therefore, the proposed model is important for improving the accuracy and reliability of WiFi RTT-based positioning because it provides the basis for solving subsequent problems. This model provides a theory to capture the moment when the communication status changes accurately. Furthermore, the ranging error drift can be corrected to obtain high-precision positioning results.
PubDate: 2022-08-11

• Vector angle grouping-based solution separation for multipath/NLOS
detection and exclusion with the enhancement of doppler test

Abstract: Abstract In urban areas, global navigation satellite system (GNSS) measurements are susceptible to multipath and non-line-of-sight (NLOS) effects, significantly degrading GNSS performance. Nowadays, multipath/NLOS effects have become the main cause of GNSS measurement fault in an urban environment. Our work mainly focuses on improving GNSS performance in urban areas without using any additional sensors. To achieve this, Doppler test-enhanced fault detection and exclusion (FDE) scheme is proposed to mitigate the influence of multipath/NLOS effects on GNSS positioning. The research is conducted in two folds. First, according to vector angle grouping (VAG) and multiple hypothesis solution separation (MHSS), the fault mode determination process is described. Since the spatial characteristic of multipath/NLOS effects are considered, the fault mode determined by VAG is able to monitor multiple measurement faults caused by multipath/NLOS effects. Second, by introducing Doppler test, Doppler test-enhanced FDE scheme is designed. The proposed FDE scheme combines VAG-based MHSS FDE and the continuity of users’ motion, which can obtain more accurate exclusion options. Experiments are carried out based on the open-source dataset, UrbanNav. The results suggest that the proposed algorithm can improve the navigation accuracy about 50% over the traditional receiver autonomous integrity monitoring-based Consistency Check method.
PubDate: 2022-08-10

• New time-differenced carrier phase approach to GNSS/INS integration

Abstract: Abstract The accuracy of navigation information is essential for modern transport systems. Such information includes position, velocity and attitude. Because of the physical characteristics of the operational environments, integration of GNSS with inertial measurement units (IMU) is commonly used. However, conventional integrated algorithms suffer from low-quality GNSS measurements due to either inaccurate pseudoranges or difficulty of ambiguity resolution when using carrier phase measurements in urban environments. We propose a Time-Difference-Carrier-Phase (TDCP) derivation controlled GNSS/IMU integration scheme. The proposed algorithm enables a TDCP-based control vector construction, including relative position, velocity, heading and pitch, which makes it possible to obtain accurate changes in position, namely delta position, altitude and velocity estimations. These estimated changes are then used to feed a loosely coupled GNSS/IMU integration system. Real-world test results show that the proposed integrated navigation scheme is superior to the conventional algorithm, with accuracy improvements of more than 38% in 3D positioning, 30% in 3D velocity, 35% in roll, 44% in pitch and 39% in heading.
PubDate: 2022-08-10

• Orbit determination of sentinel-6A using the galileo high accuracy service
test signal

Abstract: Abstract The High Accuracy Service (HAS) is an upcoming addition to the Galileo service portfolio that offers free correction data for precise point positioning in real-time. Beyond terrestrial and aeronautical applications, precise orbit determination (POD) of satellites in low Earth orbit (LEO) has been proposed as a potential use case for HAS corrections in view of their global availability. Based on HAS data collected during a test campaign in September 2021, the benefit of HAS corrections is assessed for real-time, onboard navigation as well as near real-time POD on the ground using GNSS observations of the Sentinel-6A LEO satellite. Compared to real-time POD using only broadcast ephemerides, performance improvements of about 40%, 10%, and 5% in terms of 3D position error can already be achieved for GPS-only, GPS + Galileo, and Galileo-only navigation. While Galileo processing benefits only moderately from the HAS correction data during the early tests in view of an already excellent Open Service performance, their use is highly advantageous for GPS processing and enables dual-constellation navigation with balanced contributions of both GNSSs for improved robustness. For near real-time offline POD, HAS corrections offer reduced latency or accuracy compared to established ultra-rapid GNSS orbit and clock products as well as independence from external sources.
PubDate: 2022-08-09

• A comprehensive evaluation of utilizing BeiDou data to estimate snow
depths from two ground-based stations

Abstract: Abstract The BeiDou Navigation Satellite System (BDS) of China started to provide global services in 2020, which provides a new data source for snow depth sensing through the Global Navigation Satellite System Interferometric Reflectometry (GNSS-IR) technique. This study, taking advantage of two stations in the snow season of 2020, first evaluates the performance of the five state-of-the-art snow depth models on BDS data and provides a comprehensive analysis of the characteristics of BDS data toward snow depth estimations. The results show that the snow depth estimations using the SNR, triple-frequency SNR combination (SNR_COM), and triple-frequency phase combination (F3) models are comparable, with high correlation coefficient R2 (root-mean-square error, RMSE) values of 0.93 (3.17 cm), 0.93 (3.12 cm), and 0.93 (3.27 cm), respectively. The models of geometry-free linear combinations of the phase measurements (L4) and combination of pseudorange and carrier phase of dual-frequency signals (F2C) are slightly poorer, with mean R2 (RMSE) values of 0.69 (7.18 cm) and 0.82 (4.68 cm), respectively. The snow depth retrieval results show similar accuracy using data from the BDS-3 and BDS-2 (RMSE = 3.63 cm vs. 3.72 cm). The results from the IGSO satellites are more reliable than those from the MEO satellites. The effects of satellite elevation angles and sampling rates are also analyzed to determine the optimal parameter selections (i.e., 5°–25° or 5°–30° and sampling rates < 120 s). The findings of this study can provide supporting information to determine the strategy for using BDS signals to retrieve snow depth.
PubDate: 2022-08-09

• Optimization of undifferenced and uncombined PPP stochastic model based on
covariance component estimation

PubDate: 2022-08-09

• Machine learning-based snow depth retrieval using GNSS signal-to-noise
ratio data

Abstract: Abstract GNSS-IR enables the extraction of environmental parameters such as snow depth by analyzing signal-to-noise ratio, indicating the strength of the GNSS signal. We propose a machine learning (ML) classification approach for snow depth retrieval using the GNSS-IR technique. ML classifier algorithms were studied to classify the strong and weak ground reflections using input parameters (azimuth angle, satellite elevation angle, day of year, amplitude of reflected signal, epoch number, etc.) as independent variables. GPS data collected by UNAVCO AB39 and daily snow depth data from SNOTEL Fort Yukon for a 6-year period (2015–2020) were considered. The first 4-year data were trained by some well-known ML classifiers to weight the input data and then used to classify the strong and weak signals. Tree-based classifiers, Random Forest, AdaBoost, and Gradient Boosting overperformed the other classifiers since they have more than 70% accuracy, so we performed our analysis with these three methods. The last 2-year data were used to validate both trained models and snow depth retrievals. The results show that ML classifier algorithms perform better results than traditional GNSS-IR snow depth retrieval; they improve the correlations by up to 19%. Moreover, the root-mean-square errors decrease from 15.4 to 4.5 cm. This study has a novel approach to the use of ML techniques in GNSS-IR signal classification, and the proposed methods provide a critical improvement in accuracy compared to the traditional method.
PubDate: 2022-08-08

• Robust unambiguous ranging technique for BDS-3 B1 wideband composite
signals

Abstract: Abstract During the evolution of global navigation satellite systems (GNSS), many new GNSS signals have been proposed to meet the demand of various applications for high-precision positioning. The single-sideband complex subcarrier (SCBOC) modulated signals, which are contained in China's third-generation BeiDou Navigation Satellite System (BDS-3) B1 wideband composite signals, have extremely high-precision ranging potential. Although high-precision ranging performance of SCBOC signals has been demonstrated by implementing a cross-assisted tracking (CAT) technique in previous studies, ambiguity threats are not effectively relieved, resulting in ambiguous ranging. Therefore, we propose a robust unambiguous ranging technique, which utilizes an ambiguity model established by observations derived from CAT to resolve ambiguous ranging results. Simulation experiments are implemented to quantitatively evaluate the proposed method’s performance and explore its effective ranges. Real data experiments are also implemented in static and dynamic cases to furtherly verify the effectiveness of the proposed method, exhibiting that the proposed method can take full advantage of the high-precision ranging potential contained in BDS-3 B1 wideband composite signals with less ambiguity threats.
PubDate: 2022-08-05

• Single-frequency cycle slip detection and repair based on Doppler
residuals with inertial aiding for ground-based navigation systems

Abstract: Abstract As effective backups for global navigation satellite systems (GNSS), ground-based navigation systems can provide positioning, navigation, and timing services in situations in which the GNSS signal is degraded or denied, such as city canyons, underground, and tunnels. To handle the issue of the poor performance of small cycle slip detection in single-frequency receivers, we propose a single-frequency cycle slip detection and repair method based on Doppler residuals with inertial aiding (DRIA). A low-cost micro-electro-mechanical system inertial measurement unit (MEMS-IMU) is employed in a tightly coupled integration to predict Doppler measurements of the receiver accurately. The Doppler residuals are used as test statistics for cycle slip detection in the DRIA method, obtained by subtracting the predictions from the observed Doppler measurements. The performance of the DRIA method is tested using a ground-based high-precision local positioning system (GH-LPS) in an indoor environment. The test results demonstrate effective cycle slip detection even for one cycle in real time using only single-frequency measurements. The DRIA method achieved a 91.2% success rate, which is an improvement of 207% compared with the method based on carrier phase residuals. During the entire kinematic experiment, the root mean square of the horizontal positioning error was 1.3 cm, which is an improvement of 97.6% over the unrepaired condition (54.0 cm) and 83.4% over the method based on the carrier phase residuals (8.0 cm). The experimental results indicate the validity of the Doppler residual methods for small cycle slip detection and repair, providing a new basis to deal with cycle slips in ground-based navigation systems.
PubDate: 2022-08-05

• GNSS2TWS: an open-source MATLAB-based tool for inferring daily terrestrial
water storage changes using GNSS vertical data

Abstract: Abstract Technological advances in global navigation satellite system (GNSS) offer a novel environmental sensor to measure terrestrial water cycles and provide independent constraints on total terrestrial water storage (TWS) changes over various spatiotemporal scales. This study aims to develop an open-source MATLAB-based tool for inferring daily TWS changes based on the relation between GNSS annual vertical displacement and hydrological cycles. The widely used spatial-domain Green's function approach is used to estimate regional equivalent water height changes. To recover daily water storage fluctuations, we integrate the principal component analysis into our time-varying inversion strategy. To demonstrate the implementation of the inversion tool, we invert the daily TWS changes in the Pacific Northwest River Basin, the United States of America, using GNSS-measured vertical surface motions. The primary goal is to share this inversion software for hydrogeodetic scientific communities to fully use the GNSS technique for hydrological applications.
PubDate: 2022-08-04

• Ionosphere-weighted post-processing kinematic for airborne positioning
with refined modeling of receiver phase biases and tropospheric zenith wet
delays

Abstract: Abstract The application of the global navigation satellite system (GNSS) in aviation effectively meets the requirements of aircraft location-based services. However, the GNSS application in airborne surveys mostly follows the land survey method, which ignores the particularity of the airborne flight operations, such as the rapid change of altitude difference. The present study contributes to this research trend by constructing a suitable positioning model for airborne kinematic precise positioning and analyzing the variation characteristics of receiver phase biases (RPBs) and tropospheric zenith wet delays (ZWDs) to explore their impact on airborne positioning. The ionosphere-weighted post-processing kinematic (PPK) model for long-distance high-altitude positioning is constructed by adding the between-station single-differenced ionospheric pseudo-observations. Aside from these, the correlation between the characteristics of RPBs, ZWDs, and environmental factors (temperature, vapor pressure) is analyzed and the kinematic constraint of the ionosphere-weighted PPK model on RPBs and ZWDs is adjusted based on their true variations. The results show that under the condition of large altitude differences, temperature-sensitive RPBs and ZWDs significantly impact positioning. Furthermore, pre-calibrating RPBs and ZWDs can significantly improve the ambiguity success rate and positioning performance. Based on the bias-calibrated ionosphere-weighted PPK model, the fixed solutions difference of the two common-antenna moving stations carried by the manned aircraft is stable for the positioning results of the two flight experiments. The 3-dimensional root-mean-square (3D-RMS) values are 1.4 cm and 0.5 cm, with 82% and 99% ambiguity success ratios.
PubDate: 2022-08-03

• GNSS atmosphere seismology for equatorial earthquakes: a case study from
Central America

Abstract: Abstract We study the impact of the severe equatorial earthquakes on the ionospheric Equatorial Ionization Anomaly (EIA) to check the variations in the shape of electron concentrations along the earthquake longitudes as the possible precursors to the earthquakes by considering a case study of a strong Mw 7.3 seismic event from Honduras occurred in 2009. We have observed sharp increments in the atmospheric chemical potential and surface air temperature time series along with an abrupt decrease in the relative humidity simultaneously about 5–8 days before the impending earthquake indicating the procreation of the air ionization due to increased radon activity around the earthquake's epicenter. We further investigated the ionospheric conditions by estimating the total electron content (TEC) from 6 IGS stations. The results suggested that the 2 IGS stations operating within the earthquake preparation area (EPA) showed prominent TEC enhancements about 5 days before the impending earthquake, consistent with the seismic atmospheric circulations. The other 3 IGS stations, operating outside the EPA, did not show any perturbation. These TEC variations are quantified based on two different methods: (1) running interquartile method and (2) method of cognitive recognition (applied on station BOGT). Moreover, the TEC and electron density profiles, retrieved from station BOGT and the ISL probe of the DEMETER satellite, respectively, revealed that the local TEC enhancements further dispersed toward the magnetic equator at higher altitudes by developing an enormous two-hump-like EIA structure near the epicentral longitude that verifies the generation of the seismogenic electric field through air ionization. We believe that our multi-precursory analysis is another step forward in comprehending the seismic lithosphere–ionosphere interactions.
PubDate: 2022-08-01

• A Carrier phase tracking method for vector tracking loops

Abstract: Abstract Compared with the traditional scalar tracking structure, the vector tracking structure of the satellite navigation receiver has a better signal tracking sensitivity in high dynamic and other situations. However, due to the limited accuracy, it is really hard for a vector tracking loop to maintain the lock of carrier phase. In order to solve this problem, a carrier phase tracking method for vector tracking loops is proposed. First, three common vector tracking structures are analyzed. Second, in the structure of double vector loops, phase compensation is estimated and used to improve the tracking accuracy of the carrier phase. Finally, simulations have been carried out to analyze and verify the feasibility of the proposed scheme. This method estimates and reduces the phase tracking error and has a better tracking effect than the traditional scalar structure. It provides a reference for the implementation of the vector tracking structure and the ultra-tight integrated navigation system.
PubDate: 2022-08-01

• Minimum-observation method for rapid and accurate satellite coverage
prediction

Abstract: Abstract Satellite coverage is one of the most important elements of satellite applications, which determines the range and duration of the service provided by the satellite. We propose a rapid one-dimensional method to predict when a ground target is visible from the satellite, which means the ground target is within the footprint of the satellite, for an arbitrary sensor field. The field is defined as the shape of the observable range of the sensor placed on the satellite. For instance, the cone field means the shape of the observable range of the sensor is a circle, while the rectangle field means the shape of the observable range of the sensor is a rectangle. First, the minimum-observation function is defined to describe the geometric properties of the sensor field of a satellite. Based on the geometric relationship between the satellite and a target, visible conditions at a ground point given the satellite field of view are obtained, considering the field and earth-occlusion constraints. In order to calculate the visible set during a given period, the Hermite cubic interpolation method is used to obtain the earth-occlusion-off intervals rapidly, and the field-constraint function is fitted by the linear fixed-step method. The visible intervals of the ground point from the sensor are obtained by finding the zero points of the fitting field-constraint function limited by the earth-occlusion-off intervals. To demonstrate the effectiveness of the proposed method, a series of numerical simulations are conducted. The simulation results indicate that the proposed method can balance computation time and precision, which is suitable for various types of satellite orbits and sensor fields. Thus, as a practical method, the proposed method can provide efficient communication, navigation, and remote sensing tool.
PubDate: 2022-07-31

• On the potential contribution of BeiDou-3 to the realization of the
terrestrial reference frame scale

Abstract: Abstract Since the release of the phase center calibrations for both the receivers and the satellites, the BeiDou Navigation Satellite System (BDS) became a new potential contributor to the realization of the terrestrial reference frame (TRF) scale of future International Terrestrial Reference Frame releases. This study focuses on the evaluation of the potential usage of the BDS-3 Medium Earth Orbit (MEO) constellation to the definition of the TRF scale. To that aim, we used ground calibrated BDS-3 satellite PCOs provided by the China Satellite Navigation Office and multi-GNSS robot calibrations for the ground antennas conducted by Geo++. Two ionosphere-free linear combinations of signals, namely B1I/B3I and B1C/B2a, have been investigated to find out whether using different frequencies may lead to different TRF scale definitions. Differences between the z components of the satellite phase offsets as given by manufacturer calibrations and those estimated based on IGS14 scale amount to 6.55 ± 12.56 cm and − 0.32 ± 10.99 cm for B1I/B3I and B1C/B2a frequency pairs, respectively. On the one hand, the substantial deviation from the mean reflects the disparities in the quality of calibrations for the individual spacecraft, especially those manufactured by the Shanghai Engineering Center for Microsatellites (SECM). On the other hand, the difference between the two frequency pairs arises to a great extent from the doubtful quality of the SECM PCO calibrations, which certainly do not reflect the frequency dependence of the PCOs. Eventually, the mean scale bias with respect to IGS14 equals + 0.546 ± 0.085 ppb and + 0.026 ± 0.085 ppb for B1I/B3I and B1C/B2a solutions, respectively, when using all 24 BDS-3 MEO satellites.
PubDate: 2022-07-29

• DOA tracking using an improved direction lock loop based on a
three-element L-shaped array

Abstract: Abstract Direction Lock Loop (DiLL) utilizes the direction of arrival (DOA) error obtained from the spatial correlation characteristics of the array antenna beamforming and dynamically adjusts the estimated DOA value through a closed-angle tracking loop. DiLL is a representative DOA tracking method for a direct sequence code division multiple access (DS-CDMA) system. Nevertheless, several issues prohibit employing DiLL in a global navigation satellite system (GNSS), such as limited tracking range, dead-zone effect, and separation of the capturing and tracking process. To solve these problems, we propose an improved DiLL tracking scheme based on a three-element L-shaped array named 3L-DiLL. The developed method exploits the 90-degree angular difference that naturally exists in the L-shaped array response of the normalized spatial correlation function and obtains the angular difference between the estimated and the true DOA to realize real-time DOA tracking of the target signal. Considering an incident signal of $$-180\mathrm{ to}+{180}^{\circ }$$ azimuth range and $$0-9{0}^{\circ }$$ elevation range, the proposed method tracks DOA arbitrarily and eliminates the dead zone effect. Additionally, if the estimated azimuth error is within $$[-{90}^{^\circ },+{90}^{^\circ }]$$ , capturing DOA requires only one 3L-DiLL tracking cycle. Compared with the traditional DiLL, the proposed method is simpler and easier to apply in engineering applications. Simulations verify that 3L-DiLL has a wider tracking range, faster capture speed, and higher tracking accuracy than traditional DiLL schemes.
PubDate: 2022-07-28

• Real-time precise point positioning based on BDS-3 global short message
communication

Abstract: Abstract Real-time precise point positioning (RTPPP) has obtained much attention and has been widely used in recent years, yet it depends very much on real-time precise satellite orbit and clock products. However, precise products cannot be received in regions where the Internet and mobile communication are restricted or even unavailable. We proposed a method for RTPPP based on global short message communication of BeiDou navigation satellite system (BDS-3) since it can provide two-way communication and global services. Several optimization schemes are adopted to reduce the required broadcast bandwidth due to limited resources. First, the state space representation (SSR) satellite orbit and clock corrections are combined into an equivalent distance correction. Second, all satellites broadcast the difference of pseudo-random noise (PRN) and Issue of Data Ephemeris (IODE), except that the first satellite broadcasts absolute PRN and IODE values. Last, on the basis of analyzing the relationship between product accuracy loss and positioning accuracy, the coding scheme of the satellite product is determined. Compared to the data size required to encode satellite orbit and clock products in SSR format, the proposed method can reduce this by more than 89%. Both simulated and live RTPPP experiments are conducted to verify the method proposed. For the same satellite orbit and clock corrections, the simulated results demonstrate that RTPPP based on BDS-3 GSMC corrections can provide comparable performance with SSR format products. In addition, live RTPPP based on BDS-3 GSMC equipment shows that the dynamic RTPPP can achieve positioning accuracy within 20 cm after 7 min of convergence.
PubDate: 2022-07-19

• Estimation and analysis of BDS-3 satellite yaw attitude using

Abstract: Abstract China has completed the full BDS-3 constellation with satellites manufactured, respectively, by China Academy of Space Technology (CAST) and Shanghai Engineering Center for Microsatellites (SECM). This study investigates BDS-3 satellite yaw attitudes using Ka-band inter-satellite link (ISL) observations with relatively large horizontal satellite antenna phase center offsets, which have the advantage in the satellite yaw attitude estimation and validation. Based on the ISL observation data, the BDS-3 satellite yaw angles are estimated with the reverse kinematic precise point positioning approach, and the RMS error of yaw estimates is smaller than 3°. Comparisons between nominal and estimated yaw angles demonstrate that the CAST satellites experience the midnight- or noon-turn maneuvers when the β angle lies in the range of (− 3°, 3°) and the orbital angle lies in the range of approximately (− 6°, 6°) or (174°, 186°), whereas the SECM satellites only need to meet that the β angle is in the range of (− 3°, 3°). Accordingly, the different attitude models are applicable for BDS-3 satellites from different manufacturers. However, discrepancies between the yaw directions in the vicinity of zero β angle are observed for SECM satellites. The main feature shows that the yaw attitude transition when the β angle changes sign may be delayed and occurs only when the yaw angle is within approximately ± 5°. A modified attitude model is developed to reproduce the yaw behaviors for SECM satellites more appropriately. After applying the yaw-attitude models suitable for BDS-3 CAST and SECM satellites to ISL data processing, the ISL observation residuals during yaw maneuvers are reduced down to the normal level, which confirms the effectiveness of models.
PubDate: 2022-07-17

Abstract: Abstract Global Navigation Satellite Systems allow the users to synchronize their clock on the international time reference, the Coordinated Universal Time (UTC). To that aim, they broadcast in their navigation messages a prediction of the offset between the system reference time scale GNSST and a prediction of UTC. Due to the regular update of the navigation messages at the satellite level, different satellites simultaneously broadcast different sets of parameters for the prediction of UTC. We show how the UTC broadcast parameters differ from each other within each constellation, either among the satellites or among the message types. We quantify the impact of such differences at the user level and determine the synchronization uncertainties associated with these differences in the navigation messages. Our results show that even if it depends on the constellation, the 1-sigma uncertainty on the synchronization associated with the dispersion of the navigation messages is always lower than 4 ns, while very large differences can exist on some specific signals.
PubDate: 2022-07-16

• Satellite laser ranging to GNSS-based Swarm orbits with handling of
systematic errors

Abstract: Abstract Satellite laser ranging (SLR) retroreflectors along with GNSS receivers are installed onboard numerous active low earth orbiters (LEOs) for the independent validation of GNSS-based precise orbit determination (POD) products. SLR validation results still contain many systematic errors that require special handling of various biases. For this purpose, we derive methods of reducing systematic effects affecting the SLR residuals to LEO Swarm satellites. We test solutions incorporating the estimation of range biases, station coordinate corrections, tropospheric biases, and horizontal gradients of the troposphere delays. When estimating range biases once per day, the standard deviation (STD) of Swarm-B SLR residuals is reduced from 10 to 8 mm for the group of high-performing SLR stations. The tropospheric biases estimated once per day, instead of range biases, further reduce the STD of residuals to the level of 6 mm. The systematic errors that manifest as dependencies of SLR residuals under different measurement conditions, e.g., elevation angle, are remarkably diminished. Furthermore, introducing troposphere biases allows for the comparison of the orbit quality between kinematic and reduced-dynamic orbits as the GPS-based orbit errors become more pronounced when SLR observations are freed from elevation-dependent errors. Applying tropospheric biases in SLR allows obtaining the consistency between the POD solution and SLR observations that are two times better than when neglecting to model of systematic effects and by 29% better when compared with solutions considering present methods of range bias handling.
PubDate: 2022-07-14

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