ORCID Profile
0000-0001-7060-4123
Current Organisation
Curtin University
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Navigation and Position Fixing | Geomatic Engineering | Photogrammetry and Remote Sensing | Environmental Monitoring | Transport Engineering | Automotive Safety Engineering |
ANZSRC Socio-Economic Objective (SEO)
Environmental Management Systems | Road Public Transport | Road Safety | Satellite Navigation Equipment | Road Infrastructure and Networks | Expanding Knowledge in Technology
Related Links
Publications
Modeling and assessment of atmospheric delay for GPS/Galileo/BDS PPP-RTK in regional-scale
Publisher: Elsevier BV
Date: 05-2022
Dynamic modeling of GNSS troposphere wet delay for estimation of Precipitable Water Vapour
Publisher: Walter de Gruyter GmbH
Date: 2014
Bridging Real-Time Precise Point Positioning in Natural Hazard Warning Systems during Outages of MADOCA Corrections
Publisher: Institute of Navigation
Date: 14-06-2017
DOI: 10.33012/2017.15075
Predicting orbit and clock corrections during their outage in real-time positioning using GPS, GLONASS and QZSS for natural hazard warning systems
Publisher: Walter de Gruyter GmbH
Date: 20-12-2018
Abstract: Real-time Precise Point Positioning (RT PPP) is a primary positioning method used in natural hazard warning systems (NHWS) such as monitoring tsunami and earthquakes. The method relays on precise orbit and clock corrections to eliminate satellite-related errors and its performance can be significantly improved by using measurements from multi-GNSS constellations compared with using only one system, such as GPS. The Japanese Multi-GNSS Advanced Demonstration tool for Orbit and Clock Analysis (MADOCA) provides these corrections for GPS, GLONASS and QZSS satellites enabling a multi-GNSS RT-PPP. However, the accuracy of RT PPP will suffer a major decline in case of presence of an outage in receiving these corrections, for instance due to a temporary failure of the user modem. For that reason, a method is proposed to maintain RT PPP when such a break takes place. For short outages less than 30 minutes we predict MADOCA orbits using a Holt-Winters’ auto-regressive model, and for longer outages up to 1 hr, the most recent International GNSS Service (IGS) ultra-rapid orbits can be used, but only for GPS. In addition, the clock corrections are predicted as a time series using a linear model with sinusoidal terms. The best regression period to estimate the required model parameters is discussed based on analysis of the autocorrelation of the corrections. The prediction model parameters are estimated using a sliding time window. Evaluation of the proposed method showed that positioning accuracy of 15 cm was maintained during the prediction period, which is twice better than using IGS ultra-rapid predicted products. For NHSW, the displacement errors due to prediction errors were generally within ±6 cm with one min interval and ±10 cm with five min interval.
Evaluation of real-time variometric approach and real-time precise point positioning in monitoring dynamic displacement based on high-rate (20 Hz) GPS Observations
Publisher: Springer Science and Business Media LLC
Date: 22-12-2022
Pilot Evaluation of Integrating GLONASS, Galileo and BeiDou with GPS in Araim
Publisher: Walter de Gruyter GmbH
Date: 22-02-2016
Abstract: In this pilot study, availability of the Advanced Receiver Autonomous Integrity Monitoring (ARAIM) when integrating various combinations of satellite constellations including Galileo, GLONASS and BeiDou with GPS is investigated. The Multiple Hypothesis Solution Separation method was applied using one month of real data. The data was collected at stations of known positions, located in regions that have different coverage levels by the tested constellations. While most previous studies used simulated data, the importance of using real data is twofold. It allows for the use of actual User Range Accuracy (URA) received within the satellite navigation message, which is a fundamental component for computation of the integrity protection level and the computation of vertical position errors to validate the integrity approach. Results show that the vertical position error was always bounded by the protection level during the test period and the ARAIM availability can reach 100% of the time when using all constellations even though some constellations are yet incomplete.
Performance analysis of an alternative technique for relative positioning by GPS
Publisher: IEEE
Date: 2008
Implication between Geophysical Events and the Variation of Seasonal Signal Determined in GNSS Position Time Series
Publisher: MDPI AG
Date: 02-09-2021
DOI: 10.3390/RS13173478
Abstract: The seasonal signal determined by the Global Navigation Satellite System (GNSS), which is captured in the coordinate time series, exhibits annual and semi-annual periods. This signal is frequently modelled by two periodic signals with constant litude and phase-lag. The purpose of this study is to explore the implication of different types of geophysical events on the seasonal signal in three stages—in the time span that contains the geophysical events, before and after the geophysical event, but also the stationarity phenomena, which is analysed on approximately 200 reference stations from the EPN network since 1995. The novelty of the article is demonstrated by correlating three different types of geophysical events, such as earthquakes with a magnitude greater than 6° on the Richter scale, landslides, and volcanic activity, and analysing the variation in litude of the seasonal signal. The geophysical events situated within a radius of 30 km from the epicentre showed a higher seasonal value than when the timespan did not contain a geophysical event. The presence of flicker and random walk noise was computed using overlapping Hadamard variance (OHVAR) and the non-stationary behaviour of the time series of the CORS coordinates in the time frequency analysis was done using continuous wavelet transform (CWT).
Advanced receiver autonomous integrity monitoring using triple frequency data with a focus on treatment of biases
Publisher: Elsevier BV
Date: 04-2017
Hybrid Wavelet and Principal Component Analyses Approach for Extracting Dynamic Motion Characteristics from Displacement Series Derived from Multipath-Affected High-Rate GNSS Observations
Publisher: MDPI AG
Date: 24-12-2019
DOI: 10.3390/RS12010079
Abstract: 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 litude) 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 litude 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 litudes 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 litude approaches 91.5% relative to the LVDT observations.
Prediction of RTK positioning integrity for journey planning
Publisher: Walter de Gruyter GmbH
Date: 10-2020
Abstract: Positioning integrity is crucial for Intelligent Transport Systems (ITS) applications. In this article, a method is presented for prediction of GNSS positioning integrity for ITS journey planning. This information, in addition to other route information, such as distance and time, can be utilized to choose the safest and economical route. We propose to combine the Advanced Receiver Autonomous Integrity Monitoring (ARAIM) technique, tailored for ITS, with 3D city models. Positioning is performed by GNSS Real-Time Kinematic (RTK) method, which can provide the accuracy required for ITS. A new threat model employed for computation of the protection levels (PLs) for RTK positioning is discussed. Demonstration of the proposed approach is performed through a kinematic test in an urban area in Tokyo. The comparison between the prediction method and the actual observations show that the two estimate close satellite geometry and PLs. The method produced PLs that bounds the actual position errors all the time and they were less than the preset alert limit.
On detection of observation faults in the observation and position domains for positioning of intelligent transport systems
Publisher: Springer Science and Business Media LLC
Date: 10-2019
ARAIM for Vertical Guidance Using GPS and BeiDou
Publisher: Springer Science and Business Media LLC
Date: 30-06-2013
DOI: 10.5081/JGPS.12.1.28
Integrated use of GPS and GLONASS in Support of the Redesign of Road Networks
Publisher: Cambridge University Press (CUP)
Date: 2001
DOI: 10.1017/S0373463300001235
Abstract: An integrated GPS/GLONASS system was employed in this study to support the re-design of road networks and the adjustment of traffic control. The system was used to update road maps, and to determine the velocity and acceleration of a test vehicle. The vehicle ran along the traffic stream at designated times of a day, for specific time spans, to identify traffic conditions in urban areas of uncontrolled intersections such as roundabouts. Issues addressed included: transformation of GLONASS satellite coordinates from PZ-90 to WGS-84, the presence of the receiver clock error in the GLONASS double-differenced measurements, and the impact of the carrier wavelength variation on the ambiguity resolution. Two tests were carried out in an urban environment using the combined GPS/GLONASS system. The first test included updating a road map of a test area by an RTK approach. Results were checked by comparing them with an accurate map of the area, previously determined by conventional methods. The second test comprised determining position, velocity and acceleration of a moving vehicle representing the traffic flow for a selected area. Different solution schemes were investigated, including: RTK, DGPS, and post-processing of phase measurements. The impact of GLONASS augmentation and the quality of GPS satellites on solution feasibility and accuracy were also examined. Test results showed the benefits of adopting the integrated approach. These included: improving productivity and economics of map production, and improving availability, integrity, and accuracy of determining the velocity and acceleration, linked to positions on the road networks.
Undifferenced and uncombined GNSS approach for absolute and relative POD of LEO satellites in formation flying
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-2576
Abstract: Low Earth orbit (LEO) satellites are widely used in space missions such as satellite gravimetry, radio occultation, Earth monitoring, and in formation flying. Precise orbit determination (POD), in either absolute or relative modes, is an essential prerequisite for these missions. The onboard collected signals of the global navigation satellite system (GNSS) are used for the POD of LEO satellites. Typically, the Ionosphere-free (IF) combination of these signals is used in the absolute LEO POD, which has some disadvantages. Firstly, the observation information is wasted in constructing IF observation. Secondly, although different IF combinations can be constructed in multi-frequency scenarios, they may be correlated. Thirdly, integer ambiguity resolution (IAR) based on the IF observations can only be achieved with precise external products, which has limited availability in space. Concerning relative POD, the most classical method is the double-differenced (DD) model with IAR, which also has drawbacks. Firstly, strict common-view GNSS satellites are needed, which is not guaranteed in the complex space environment with the high dynamic of the satellites. Secondly, the opportunity to impose dynamic constraints on the eliminated parameters is lost during differencing. Therefore, in this contribution, we focus on the use of undifferenced uncombined (UDUC) observations and propose a new POD model. The UDUC POD model has several advantages. Firstly, the common-view GNSS satellites are only used to form the DD ambiguities for IAR therefore, there is no need for the external satellite phase bias (SPB) products. Secondly, the model shows flexibility in multi-frequency scenarios. Thirdly, and more importantly, as precise GNSS orbits and clocks products are used, the model can be used for both absolute and relative LEO POD. Based on onboard GPS observations of a formation flying mission, comprising two closely spaced LEO satellites working in a formation, we explored the performance improvement of the proposed model over traditional models. Two conclusions can be drawn. Firstly, the proposed model's performance in absolute POD is improved by more than 20% compared with the classical IF POD method, when computing their differences with reference orbits. Secondly, for relative POD, it is proposed that the consistency between the model and the reference orbit is within 1.5 mm, proving that the method can serve for formation flying missions. The above results show that the proposed UDUC POD method can achieve higher POD accuracy than the traditional methods.
Using peer assessment of fieldwork to enhance students’ practical training
Publisher: Informa UK Limited
Date: 29-07-2013
Prediction of troposphere wet delay
Publisher: Walter de Gruyter GmbH
Date: 2011
DOI: 10.1515/JAG.2011.015
Machine automation using RTK GPS positioning
Publisher: IEEE
Date: 03-2009
Triple-frequency GNSS models for PPP with float ambiguity estimation: performance comparison using GPS
Publisher: Informa UK Limited
Date: 02-12-2016
A method for precise point positioning with integer ambiguity resolution using triple-frequency GNSS data
Publisher: IOP Publishing
Date: 10-05-2019
Attitude Determination from GNSS Using Adaptive Kalman Filtering
Publisher: Cambridge University Press (CUP)
Date: 2005
DOI: 10.1017/S0373463304003042
Abstract: An adaptive Kalman filtering approach is proposed for attitude determination to replace the fixed (conventional) Kalman filtering approach. The filter is used to adaptively reflect system dynamics changes or rapid changes in vehicle trajectory. The estimation procedure is carried out through the use of a measurement residual sequence. The sequence is used as a piece-wise stationary process inside an estimation window. The measurement noise covariance matrix and the system noise matrix are adaptively estimated. An extended Kalman filter approach with iteration of the states within-an-epoch was performed to overcome the non-linearity of the observation equations. A test was performed to evaluate the proposed technique. Different trajectory scenarios are presented to show the difference in performance between the adaptive Kalman filter and the conventional one. Results show that the proposed adoptive filtering approach has a better performance than the conventional filter.
URE and URA for predicted LEO satellite orbits at different altitudes
Publisher: Elsevier BV
Date: 10-2022
Proposed Orbital Products for Positioning Using Mega-Constellation LEO Satellites
Publisher: MDPI AG
Date: 14-10-2020
DOI: 10.3390/S20205806
Abstract: With thousands of low Earth orbit (LEO) satellites to be launched in the near future, LEO mega-constellations are supposed to significantly change the positioning and navigation service for ground users. The goal of this contribution is to suggest and discuss the feasibility of possible procedures to generate the LEO orbital products at two accuracy levels to facilitate different positioning methods—i.e., Level A orbits with meter-level accuracy as LEO-specific broadcast ephemeris, and Level B orbits with an accuracy of centimeters as polynomial corrections based on Level A orbits. Real data of the LEO satellite GRACE FO-1 are used for analyzing the error budgets. For the Level A products, compared to the orbital user range errors (OUREs) of a few centimeters introduced by the ephemeris fitting, it was found that the orbital prediction errors play the dominant role in the total error budget—i.e., at around 0.1, 0.2 and 1 m for prediction intervals of 1, 2 and 6 h, respectively. For the Level B products, the predicted orbits within a short period of up to 60 s have an OURE of a few centimeters, while the polynomial fitting OUREs can be reduced by a few millimeters when increasing the polynomial degree from one to two.
On hypothesis testing in RAIM algorithms: generalized likelihood ratio test, solution separation test and a possible alternative
Publisher: IOP Publishing
Date: 21-05-2019
Quality Control in Using GNSS CORS Network for Monitoring Plate Tectonics: A Western Australia Case Study
Publisher: American Society of Civil Engineers (ASCE)
Date: 05-2016
Integrity Monitoring for Advanced Driver Assistance Systems
Publisher: Institute of Navigation
Date: 08-11-2016
DOI: 10.33012/2016.14598
Ionosphere Augmentation for Accelerated Convergence in Precise Point Positioning with Triple-frequency and GPS
Publisher: Institute of Navigation
Date: 14-06-2017
DOI: 10.33012/2017.15101
Precise Point Positioning in the Airborne Mode
Publisher: Walter de Gruyter GmbH
Date: 2011
Estimation of multi-constellation GNSS observation stochastic properties using single receiver single satellite data validation method
Publisher: Informa UK Limited
Date: 27-04-2014
Maintaining real-time precise point positioning during outages of orbit and clock corrections
Publisher: Springer Science and Business Media LLC
Date: 19-11-2016
A Sensitivity Study of POD Using Dual-Frequency GPS for CubeSats Data Limitation and Resources
Publisher: MDPI AG
Date: 07-2020
DOI: 10.3390/RS12132107
Abstract: Making use of dual-frequency (DF) global navigation satellite system (GNSS) observations and good dynamic models, the precise orbit determination (POD) for the satellites on low earth orbits has been intensively investigated in the last decades and has achieved an accuracy of centimeters. With the rapidly increasing number of the CubeSat missions in recent years, the POD of CubeSats were also attempted with combined dynamic models and GNSS DF observations. While comprehensive dynamic models are allowed to be used in the postprocessing mode, strong constraints on the data completeness, continuity, and restricted resources due to the power and size limits of CubeSats still h er the high-accuracy POD. An analysis of these constraints and their impact on the achievable orbital accuracy thus needs to be considered in the planning phase. In this study, with the focus put on the use of DF GNSS data in postprocessing CubeSat POD, a detailed sensitivity analysis of the orbital accuracy was performed w.r.t. the data continuity, completeness, observation s ling interval, latency requirements, availability of the attitude information, and arc length. It is found that the overlapping of several constraints often causes a relatively large degradation in the orbital accuracy, especially when one of the constraints is related to a low duty-cycle of, e.g., below 40% of time. Assuming that the GNSS data is properly tracked except for the assumed constraints, and using the International GNSS Service (IGS) final products or products from the IGS real-time service, the 3D orbital accuracy for arcs of 6 h to 24 h should generally be within or around 1 dm, provided that the limitation on data is not too severe, i.e., with a duty-cycle not lower than 40% and an observation s ling interval not larger than 60 s.
Integrity monitoring of vehicle positioning in urban environment using RTK-GNSS, IMU and speedometer
Publisher: IOP Publishing
Date: 03-03-2017
Positioning Integrity, Availability and Precision for Journey Planning and Navigation using GNSS Integrated with Low-Cost Sensors
Publisher: Institute of Navigation
Date: 26-10-2018
DOI: 10.33012/2018.16028
Limited sensitivity analysis of ARAIM availability for LPV-200 over Australia using real data
Publisher: Elsevier BV
Date: 2016
On-the-Fly Prediction of Orbit Corrections for RTK Positioning
Publisher: Cambridge University Press (CUP)
Date: 06-04-2006
DOI: 10.1017/S0373463306003730
Abstract: In this study, a method is presented to maintain real-time positioning at the decimetre-level accuracy during breaks in reception of the measurement corrections from multiple reference stations. The method is implemented at the rover by estimating prediction coefficients of the corrections during normal RTK positioning, and uses these coefficients to predict the corrections when reception of the corrections is temporarily lost. The paper focuses on one segment of this method, the on-the-fly prediction of orbital corrections. Frequently, only a few minutes of data representing short orbit ‘arcs’ are available to the user before losing radio transmission. Thus, it would be hard for the rover to predict the satellite positions using equations of motion. An alternative method is proposed. In this method, GPS orbital corrections are predicted as a time series and are added to the initial positions computed from the broadcast ephemeris to compute relatively accurate satellite positions. Different prediction approaches were investigated. Results show that the double exponential smoothing method and Winters' method can be successfully applied. The latter, however, has a better performance. The impact of the data length used for estimation of the prediction coefficients and the selection of seasonal lengths in Winters' method were investigated and some values were recommended. In general, the method can give orbital correction estimation accuracy of less than 5 cm after 15 minutes of prediction. This will result in a positioning accuracy better than 5 cm.
Integrity monitoring for kinematic precise point positioning in open-sky environments with improved computational performance
Publisher: IOP Publishing
Date: 05-05-2022
Abstract: Positioning integrity monitoring (IM) is essential for liability- and safety-critical land applications such as road transport. IM methods such as solution separation apply multiple filters, which necessitates the use of computationally efficient algorithms in real-time applications. In this contribution, a new approach that significantly improves the computation time of the measurement update of the Kalman filter is presented, where only one matrix inversion is applied for all filters with measurement subsets. The fault detection and identification method and computation of the protection levels (PLs) are discussed. The computational improvement comes at the expense of a small increase in the PL. Test results for precise point positioning (PPP) with float ambiguities in an open-sky and suburban environment demonstrate the reduced computation time using the proposed approach compared to the traditional method, with 23% – 42% improvement. The availability of IM for PPP, i.e. when the PL is less than a selected alert limit of 1.625 m, ranged between 92% and 99%, depending on the allowable integrity risk, tested at 10 −5 and 10 −6 , and the observation environment.
Evaluation of multi-GNSS high-rate relative positioning for monitoring dynamic structural movements in the urban environment
Publisher: Informa UK Limited
Date: 2020
An investigation into the correlations among GNSS observations and their impact on height and zenith wet delay estimation for medium and long baselines
Publisher: Informa UK Limited
Date: 12-2012
Impact of predicting real-time clock corrections during their outages on precise point positioning
Publisher: Informa UK Limited
Date: 26-11-2017
Stability of CubeSat Clocks and Their Impacts on GNSS Radio Occultation
Publisher: MDPI AG
Date: 13-01-2022
DOI: 10.3390/RS14020362
Abstract: Global Navigation Satellite Systems’ radio occultation (GNSS-RO) provides the upper troposphere-lower stratosphere (UTLS) vertical atmospheric profiles that are complementing radiosonde and reanalysis data. Such data are employed in the numerical weather prediction (NWP) models used to forecast global weather as well as in climate change studies. Typically, GNSS-RO operates by remotely sensing the bending angles of an occulting GNSS signal measured by larger low Earth orbit (LEO) satellites. However, these satellites are faced with complexities in their design and costs. CubeSats, on the other hand, are emerging small and cheap satellites the low prices of building them and the advancements in their components make them favorable for the GNSS-RO. In order to be compatible with GNSS-RO requirements, the clocks of the onboard receivers that are estimated through the precise orbit determination (POD) should have short-term stabilities. This is essential to correctly time tag the excess phase observations used in the derivation of the GNSS-RO UTLS atmospheric profiles. In this study, the stabilities of estimated clocks of a set of CubeSats launched for GNSS-RO in the Spire Global constellation are rigorously analysed and evaluated in comparison to the ultra-stable oscillators (USOs) onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC-2) satellites. Methods for improving their clock stabilities are proposed and tested. The results (i) show improvement of the estimated clocks at the level of several microseconds, which increases their short-term stabilities, (ii) indicate that the quality of the frequency oscillator plays a dominant role in CubeSats’ clock instabilities, and (iii) show that CubeSats’ derived UTLS (i.e., tropopause) atmospheric profiles are comparable to those of COSMIC-2 products and in situ radiosonde observations, which provided external validation products. Different comparisons confirm that CubeSats, even those with unstable onboard clocks, provide high-quality RO profiles, comparable to those of COSMIC-2. The proposed remedies in POD and the advancements of the COTS components, such as chip-scale atomic clocks and better onboard processing units, also present a brighter future for real-time applications that require precise orbits and stable clocks.
Crustal Deformation Across and beyond Central Europe and Its Impact on Land Boundaries
Publisher: MDPI AG
Date: 12-02-2021
DOI: 10.3390/RESOURCES10020015
Abstract: Land is a critical and limited natural resource. The Land Administration System (LAS) has been developed to resolve and adjudicate over any disputes that might arise concerning the rights and boundaries of land. Land registration and cadastre are types of land recording that need to be established. To secure the property rights, we must be sure of accuracy of the boundary points determining the size of the property. However, in addition to typical factors considered when determining the boundary point positions, such as accuracy of geodetic networks and measurement errors, the global and local crustal deformation, resulting, e.g., from the movement of tectonic plates, should be considered. In this work, the focus is on the movement of points inside the European plate due to tectonic movement, without taking into account local events caused by erosion, landslides, etc. The study area is Europe, and particular attention was paid to Poland, which is located in the centre of the European continent and does not have significant anomalous sub-areas, making it an authoritative research object. In this study, we analysed the velocity of point displacements and the boundary deformation, using GPS observations. For this reason, we used both global (IGS) and regional (ETRF) reference frames, to show differences in point velocities for the studied areas. Overall, for the needs of the real estate cadastre in Poland, information about parcel boundary points must be obtained with an accuracy better than 0.30 m. Within 25 years, the border mark may be shifted by 0.13 m due to tectonic plate movement, which is within the required accuracy. Pursuant to the current legal regulations, the measurements of the boundary points can be performed with any method, ensuring the required accuracy (0.30 m). The most commonly used are direct measurements (GNSS and tacheometry) and photogrammetric measurements. It is recommended that periodic verifications and update of the cadastre data in Poland be carried out at least once every 15 years. In the case of such relatively frequent verification and possible modernisation of data, the potential impact of tectonic plate movement on the relative boundary point displacement can be ignored, particularly in the short term. However, for a long time period it has an influence. We suggest “relatively frequent” cadastral boundary verification to be able to ignore such influence.
Precise Orbit Determination of LEO Satellites Based on Undifferenced GNSS Observations
Publisher: American Society of Civil Engineers (ASCE)
Date: 02-2022
Integrity Monitoring for Horizontal RTK Positioning: New Weighting Model and Overbounding CDF in Open-Sky and Suburban Scenarios
Publisher: MDPI AG
Date: 06-04-2020
DOI: 10.3390/RS12071173
Abstract: Integrity monitoring is an essential task for ensuring the safety of positioning services. Under a selected probability of hazardous misleading information, the protection levels (PLs) are computed according to a considered threat model to bound the positioning errors. A warning message is sent to users when the PL exceeds a pre-set alert limit (AL). In the short-baseline real-time relative kinematic positioning, the spatially correlated errors, such as the the orbital errors and the atmospheric delays are significantly reduced. However, the remaining atmospheric residuals and the multipath that are not considered in the observation model could directly bias the positioning results. In this contribution, these biases are analysed with the focus put on the multipath effects in different measurement environments. A new observation weighting model considering both the elevation angle and the signal-to-noise ratios is developed and their impacts on the positional results are investigated. The coefficients of the proposed weighting model are determined for the open-sky and the suburban scenarios with the positional benefits maximised. Next, the overbounding excess-mass cumulative distribution functions (EMCs) are searched on the between-receiver level for the weighted phase and code observations in these two scenarios. Based on the mean and standard deviations of these EMCs, horizontal protection levels (HPLs) are computed for the ambiguity-fixed solutions of real experiments. The HPLs are compared with the horizontal positioning errors (HPEs) and the horizontal ALs (HALs). Using the sequential exclusion algorithm developed for the ambiguity resolution in this contribution, the full ambiguity resolution can be achieved in around 100% and 95% of the time for the open-sky and the suburban scenarios, respectively. The corresponding HPLs of the ambiguity-fixed solutions are at the sub-dm to dm-level for both scenarios, and all the valid ambiguity-fixed HPLs are below a HAL of 0.5 m. For the suburban scenario with more complicated multipath environments, the HPLs increase by considering extra biases to account for multipath under a certain elevation threshold. In complicated multipath environments, when this elevation threshold is set to 30 degrees, the availability of the ambiguity-fixed solutions could decrease to below 50% for applications requiring HAL as low as 0.1 m.
Second Generation SBAS – Performance Analysis and Bridging Positioning and Integrity Monitoring during SBAS Outages in the Urban Environment
Publisher: Institute of Navigation
Date: 11-10-2019
DOI: 10.33012/2019.16923
Reliable Positioning and Journey Planning for Intelligent Transport Systems
Publisher: IntechOpen
Date: 04-2020
Integrity Monitoring of PPP-RTK Positioning; Part II: LEO Augmentation
Publisher: MDPI AG
Date: 26-03-2022
DOI: 10.3390/RS14071599
Abstract: Low Earth orbit (LEO) satellites benefit future ground-based positioning with their high number, strong signal strength and high speed. The rapid geometry change with the LEO augmentation offers acceleration of the convergence of the precision point positioning (PPP) solution. This contribution discusses the influences of the LEO augmentation on the precise point positioning—real-time kinematic (PPP-RTK) positioning and its integrity monitoring. Using 1 Hz simulated data around Beijing for global positioning system (GPS)/Galileo/Beidou navigation satellite system (BDS)-3 and the tested LEO constellation with 150 satellites on L1/L5, it was found that the convergence of the formal horizontal precision can be significantly shortened in the ambiguity-float case, especially for the single-constellation scenarios with low precision of the interpolated ionospheric delays. The LEO augmentation also improves the efficiency of the user ambiguity resolution and the formal horizontal precision with the ambiguities fixed. Using the integrity monitoring (IM) procedure introduced in the first part of this series of papers, the ambiguity-float horizontal protection levels (HPLs) are sharply reduced in various tested scenarios, with an improvement of more than 60% from 5 to 30 min after the processing start. The ambiguity-fixed HPLs can generally be improved by 10% to 60% with the LEO augmentation, depending on the global navigation satellite system (GNSS) constellations used and the precision of the ionospheric interpolation.
Real-Time Determination of Orthometric Heights Accurate to the Centimeter Level Using a Single GPS Receiver: Case Study
Publisher: American Society of Civil Engineers (ASCE)
Date: 02-2006
Investigating Performance of High-Rate GNSS-PPP and PPP-AR for Structural Health Monitoring: Dynamic Tests on Shake Table
Publisher: American Society of Civil Engineers (ASCE)
Date: 02-2021
Real-Time LEO Satellite Orbits Based on Batch Least-Squares Orbit Determination with Short-Term Orbit Prediction
Publisher: MDPI AG
Date: 26-12-2022
DOI: 10.3390/RS15010133
Abstract: The augmentation of the Global Navigation Satellite System (GNSS) by Low Earth Orbit (LEO) satellites is proposed as an effective method to improve the precision and shorten the convergence time of Precise Point Positioning (PPP). Serving as navigation satellites in the future, LEO satellites need to be provided with their high-accuracy orbits in real-time. This would potentially enable the high-accuracy real-time LEO satellite clock determination, and eventually facilitate the high-accuracy ground-based positioning. Studies have been performed to achieve such real-time orbits using a Kalman filter in both the kinematic and reduced-dynamic modes. Batch Least-Squares (BLS) adjustment delivers more stable orbits in near-real-time, as it performs better phase screening. However, it suffers from longer delays compared to the Kalman filter. With the LEO satellite orbit prediction strategies improved over time, this latency can be bridged by short-term orbit prediction. In this study, using real-time GNSS satellite products, the real-time LEO satellite orbits are obtained based on the batch least-squares adjustment and short-term prediction. LEO ephemeris parameters are generated within specific prediction time windows. Using real data from the 500 km GRACE C satellite and 810 km Sentinel-3B satellite, the near-real-time BLS Precise Orbit Determination (POD) results exhibit good accuracy with an Orbital User Range Error (OURE) of 2–4 cm using different real-time GNSS products. A range of delays of the BLS POD processes are assumed, based on tests performed on different processing machines, leading to various prediction windows, from 3–8 min to 12–17 min that correspond to the real-time usage. The orbital prediction errors are shown to be highly correlated with the orbital height and the prediction time. The computational efficiency thus becomes essential to reduce the prediction errors for a certain LEO satellite. For advanced processing units leading to a prediction window shorter or equal to 6–11 min, one can expect a total real-time orbital error budget of 3–5 cm, provided that an appropriate prediction strategy is applied and high-quality GNSS products are used. For a given fitting interval, the ephemeris fitting errors are generally related to the number of ephemeris parameters and the orbital height. Compared with the prediction errors, the ephemeris fitting errors do not play a significant role in the total error budget when using 22 ephemeris parameters.
LEO satellite clock analysis and prediction for positioning applications
Publisher: Informa UK Limited
Date: 08-06-2021
POD of small LEO satellites based on precise real-time MADOCA and SBAS-aided PPP corrections
Publisher: Springer Science and Business Media LLC
Date: 11-01-2021
Integrity monitoring for Positioning of intelligent transport systems using integrated RTK‐GNSS, IMU and vehicle odometer
Publisher: Institution of Engineering and Technology (IET)
Date: 19-07-2018
Telemetric Control of Remote Vehicles using an Inverse RTK Technique
Publisher: Cambridge University Press (CUP)
Date: 2003
DOI: 10.1017/S0373463302002047
Abstract: In this study, an inverse Real Time Kinematic (RTK) GPS positioning approach is presented and discussed. GPS data from a remote receiver mounted on an unmanned vehicle is sent to the base station to determine the vehicle location at the centimetre level of accuracy in real time. Control of the vehicle's movement and manoeuvring can thus take place at the base station, which could be a few kilometres away, and the vehicle can be sent to specific locations to do certain tasks. Two GPS antennas were used in order to increase positioning reliability and estimate real time heading and pitch of the vehicle for better control. In addition, the vehicle was fitted with cameras with wireless video transmission to provide the operator with a good level of vision in different directions during operation. The main applications of such a system would be in exploration, breaching and clearance of minefields, and hazardous situations such as fire fighting of burning oil wells. The system design and techniques employed are discussed first. Issues addressed include antenna layout, data transmission, solution algorithm, and ambiguity resolution. The proposed system was mounted on a prototype vehicle and tested under different satellite visibility conditions. Results show that high positioning accuracy with reliable ambiguity resolution can be obtained with the developed approach if the number of observed satellites is 5 or more and PDOP is less than 5. Heading and pitch were determined within 0·2–0·3 degree using a 1·2 m long baseline. This performance can be improved as the length of the on-board baseline increases.
First results of using the second generation SBAS in Australian urban and suburban road environments
Publisher: Informa UK Limited
Date: 02-10-2019
Simultaneous Localization and Mapping (SLAM) for Autonomous Driving: Concept and Analysis
Publisher: MDPI AG
Date: 20-02-2023
DOI: 10.3390/RS15041156
Abstract: The Simultaneous Localization and Mapping (SLAM) technique has achieved astonishing progress over the last few decades and has generated considerable interest in the autonomous driving community. With its conceptual roots in navigation and mapping, SLAM outperforms some traditional positioning and localization techniques since it can support more reliable and robust localization, planning, and controlling to meet some key criteria for autonomous driving. In this study the authors first give an overview of the different SLAM implementation approaches and then discuss the applications of SLAM for autonomous driving with respect to different driving scenarios, vehicle system components and the characteristics of the SLAM approaches. The authors then discuss some challenging issues and current solutions when applying SLAM for autonomous driving. Some quantitative quality analysis means to evaluate the characteristics and performance of SLAM systems and to monitor the risk in SLAM estimation are reviewed. In addition, this study describes a real-world road test to demonstrate a multi-sensor-based modernized SLAM procedure for autonomous driving. The numerical results show that a high-precision 3D point cloud map can be generated by the SLAM procedure with the integration of Lidar and GNSS/INS. Online four–five cm accuracy localization solution can be achieved based on this pre-generated map and online Lidar scan matching with a tightly fused inertial system.
Local Statistical Testing in Quality Control of GNSS Observations
Publisher: Springer Science and Business Media LLC
Date: 20-06-2010
DOI: 10.5081/JGPS.9.1.12
Using Local Knowledge and Remote Sensing in the Identification of Informal Settlements in Riyadh City, Saudi Arabia
Publisher: MDPI AG
Date: 06-08-2023
DOI: 10.3390/RS15153895
Abstract: Urban planning within Riyadh, the capital of Saudi Arabia, has been impacted by the presence of informal settlements. An understanding of the spatial distribution of these settlements is essential in developing urban policies. This study used remotely sensed imagery to evaluate and characterize informal settlements within the city, both with and without expert knowledge of the study area (defined as expert knowledge, EK). An informal settlement ontology for four study sites within Riyadh City was developed using an analytical hierarchy process (AHP). Local knowledge was translated into a ruleset to identify and map settlement areas using spatial, spectral, textural, and geometric techniques. These were combined with an object-based image analysis (OBIA) approach. The study demonstrated that combining expert knowledge and remotely sensed data can efficiently and accurately identify informal settlements. Two classified images were produced, one with EK, and one without EK, to investigate how a detailed understanding of local conditions could affect the final image classification. Overall accuracy when using EK was 94%, with a kappa coefficient of 89%, while without EK accuracy was 68% (kappa coefficient of 61%). The final OBIA classes included formal and informal settlements, road networks, vacant blocks, shaded areas, and vegetation. This study demonstrated that local expert knowledge and OBIA helpful in urban mapping. It also indicated the value of integrating a local ontological process during digital image classification. This work provided improved techniques for mapping informal settlements in Middle Eastern cities.
Preliminary performance analysis of a prototype DFMC SBAS service over Australia and Asia-Pacific
Publisher: Elsevier BV
Date: 09-2020
The Stability of Tide Gauges in the South Pacific Determined from Multiepoch Geodetic Levelling, 1992 to 2010
Publisher: Informa UK Limited
Date: 09-2013
Integrity Monitoring: From Airborne to Land Applications
Publisher: InTech
Date: 30-05-2018
Alternative Postprocessing Relative Positioning Approach Based on Precise Point Positioning
Publisher: American Society of Civil Engineers (ASCE)
Date: 05-2009
Precise point positioning with decimetre accuracy using wide-lane ambiguities and triple-frequency GNSS data
Publisher: Walter de Gruyter GmbH
Date: 24-03-2020
Abstract: This paper proposes precise point positioning (PPP) methods that offer an accuracy of a few decimetres (dm) with triple frequency GNSS data. Firstly, an enhanced triple frequency linear combination is presented for rapid fixing of the extra wide-lane (EWL) and wide-lane (WL) ambiguities for GPS, Beidou-2 and Galileo. This has improved performance compared to the Melbourne-Wübbena (MW) linear combination, and has 6.7 % lower measurement noise for the GPS L1/L2 signals, 12.7 % for L1/L5 and 0.7 % for L2/L5. Analysis with tested data showed a 5–6 % reduction in time required to fix the N 21 {N_{21}} and N 51 {N_{51}} ambiguities. Once the EWL/WL ambiguities are fixed with the proposed linear combinations, three methods are presented that aim to provide positioning accuracy of a few dm. In the first approach, the three EWL/WL ambiguities in their respective phase equations are used to derive a low-noise ionosphere-free (IF) linear combination. The second method uses a low noise IF combination with two carrier-phase EWL/WL equations and a single pseudorange measurement. The third method uses a low noise IF combination with a single carrier phase EWL equation and two pseudorange measurements. These proposed methods can provide dm level positioning accuracy if carrier phase measurements with mm precision is tracked by the receiver. When comparing these combinations with a combination proposed in [22], it is found that superior performance is achieved with the third method when carrier phase noise is –6 mm for GPS and Beidou-2 and –3 mm for Galileo. This model only requires the EWL ambiguity to be fixed which typically takes just one epoch of data. Thus, the user achieves instant decimetre level PPP accuracy.
Comparison of advanced troposphere models for aiding reduction of PPP convergence time in Australia
Publisher: Informa UK Limited
Date: 24-05-2018
Validation of BeiDou Observations
Publisher: Walter de Gruyter GmbH
Date: 2014
Abstract: This study presents validation of BeiDou measurements in un-differenced standalone mode and experimental results of its application for real data. A reparameterized form of the unknowns in a geometry-free observation model was used. Observations from each satellite are independently screened using a local modeling approach. Main advantages include that there is no need for computation of inter-system biases and no satellite navigation information are needed. Validation of the triple-frequency BeiDou data was performed in static and kinematic modes, the former at two continuously operating reference stations in Australia using data that span two consecutive days and the later in a walking mode for three hours. The use of the validation method parameters for numerical and graphical diagnostics of the multi-frequency BeiDou observations are discussed. The precision of the system’s observations was estimated using an empirical method that utilizes the characteristics of the validation statistics. The capability of the proposed method is demonstrated in detection and identification of artificial errors inserted in the static BeiDou data and when implemented in a single point positioning processing of the kinematic test.
Integrity monitoring for precise orbit determination of LEO satellites
Publisher: Springer Science and Business Media LLC
Date: 24-12-2021
DOI: 10.1007/S10291-021-01200-4
Abstract: Due to an increasing requirement for high accuracy orbital information for low Earth orbit (LEO) satellites, precise orbit determination (POD) of LEO satellites is a topic of growing interest. To assure the safety and reliability of the applications requiring high accuracy LEO orbits in near-real-time, integrity monitoring (IM) is an essential operation of the POD process. In this contribution, the IM strategy for LEO POD in both the kinematic and reduced-dynamic modes is investigated. The overbounding parameters of the signal-in-space range error are investigated for the GPS products provided by the International GNSS Service’s Real-Time Service and the Multi-GNSS Advanced Demonstration of Orbit and Clock Analysis service. Benefiting from the dynamic models used and the improved model strength, the test results based on the data of the LEO satellite GRACE FO-1 show that the average-case mean protection levels (PLs) can be reduced from about 3–4 m in the kinematic mode to about 1 m in the reduced-dynamic mode in the radial, along-track and cross-track directions. The overbounding mean values of the SISRE play the dominant role in the final PLs. In the reduced-dynamic mode and average-case projection, the IM availabilities reach above 99% in the radial, along-track and cross-track directions with the alert limit (AL) set to 2 m. The values are still above 98% with the AL set to 4 m, when the duty cycle of tracking is reduced to 40%, e.g., in the case of power limits for miniature satellites such as CubeSats.
Performance evaluation of different troposphere delay models and mapping functions
Publisher: Elsevier BV
Date: 02-2013
Performance Analysis of Using the Next generation Australian SBAS with Precise Point Positioning Capability For Intelligent Transport Systems
Publisher: IEEE
Date: 04-2019
Precise Orbit Determination of CubeSats Using Proposed Observations Weighting Model
Publisher: Springer International Publishing
Date: 2022
Abstract: CubeSats can be used for many space missions and Earth science applications if their orbits can be determined precisely. The Precise Orbit Determination (POD) methods are well developed for large LEO satellites during the last two decades. However, CubeSats are built from Commercial Off-The-Shelf (COTS) components and have their own characteristics, which need more investigations. In this paper, precise orbits of 17 3U-CubeSats in the Spire Global constellation are determined using both the reduced-dynamic and the kinematic POD methods. The limitations in using elevation-dependent weighting models for CubeSats POD are also discussed and, as an alternative approach, a weighting model based on the Signal-to-Noise Ratio (SNR) has been proposed. One-month processing of these CubeSats revealed that around 40% of orbits can be determined at the decimeter accuracy, while 50% have accuracy at centimeters. Such precise orbits fulfil most mission requirements that require such POD accuracy. Internal validation methods confirmed the POD procedure and approved the distinction of weighting based on SNR values over the elevation angles.
A GPS Spoofing Generator Using an Open Sourced Vector Tracking-Based Receiver
Publisher: MDPI AG
Date: 16-09-2019
DOI: 10.3390/S19183993
Abstract: Spoofing can seriously threaten the use of the Global Positioning System (GPS) in critical applications such as positioning and navigation of autonomous vehicles. Research into spoofing generation will contribute to assessment of the threat of possible spoofing attacks and help in the development of anti-spoofing methods. However, the recent commercial off-the-shelf (COTS) spoofing generators are expensive and the technology implementation is complicated. To address the above problem and promote the GPS safety-critical applications, a spoofing generator using a vector tracking-based software-defined receiver is proposed in this contribution. The spoofing generator aims to modify the raw signals by cancelling the actual signal component and adding the spoofing signal component. The connections between the spreading code and carrier, and the states of the victim receiver are established through vector tracking. The actual signal can be predicted effectively, and the spoofing signal will be generated with the spoofing trajectory at the same time. The experimental test results show that the spoofing attack signal can effectively mislead the victim receiver to the designed trajectory. Neither the tracking channels nor the positioning observations have abnormal changes during this processing period. The recent anti-spoofing methods cannot detect this internal spoofing easily. The proposed spoofing generator can cover all open-sky satellites with a high quality of concealment. With the superiority of programmability and ersity, it is believed that the proposed method based on an open source software-defined receiver has a great value for anti-spoofing research of different GNSS signals.
Analysis of Web-Based GNSS Post-Processing Services for Static and Kinematic Positioning Using Short Data Spans
Publisher: Informa UK Limited
Date: 10-2011
Integrity Monitoring of PPP-RTK Positioning; Part I: GNSS-Based IM Procedure
Publisher: MDPI AG
Date: 23-12-2021
DOI: 10.3390/RS14010044
Abstract: Nowadays, integrity monitoring (IM) is required for erse safety-related applications using intelligent transport systems (ITS). To ensure high availability for road transport users for in-lane positioning, a sub-meter horizontal protection level (HPL) is expected, which normally requires a much higher horizontal positioning precision of, e.g., a few centimeters. Precise point positioning-real-time kinematic (PPP-RTK) is a positioning method that could achieve high accuracy without long convergence time and strong dependency on nearby infrastructure. As the first part of a series of papers, this contribution proposes an IM strategy for multi-constellation PPP-RTK positioning based on global navigation satellite system (GNSS) signals. It analytically studies the form of the variance-covariance (V-C) matrix of ionosphere interpolation errors for both accuracy and integrity purposes, which considers the processing noise, the ionosphere activities and the network scale. In addition, this contribution analyzes the impacts of erse factors on the size and convergence of the HPLs, including the user multipath environment, the ionosphere activity, the network scale and the horizontal probability of misleading information (PMI). It is found that the user multipath environment generally has the largest influence on the size of the converged HPLs, while the ionosphere interpolation and the multipath environments have joint impacts on the convergence of the HPL. Making use of 1 Hz data of Global Positioning System (GPS)/Galileo/Beidou Navigation Satellite System (BDS) signals on L1 and L5 frequencies, for small- to mid-scaled networks, under nominal multipath environments and for a horizontal PMI down to 2×10−6, the ambiguity-float HPLs can converge to 1.5 m within or around 50 epochs under quiet to medium ionosphere activities. Under nominal multipath conditions for small- to mid-scaled networks, with the partial ambiguity resolution enabled, the HPLs can converge to 0.3 m within 10 epochs even under active ionosphere activities.
Integrity monitoring using multi-GNSS pseudorange observations in the urban environment combining ARAIM and 3D city models
Publisher: Informa UK Limited
Date: 11-03-2020
GNSS multi-frequency receiver single-satellite measurement validation method
Publisher: Springer Science and Business Media LLC
Date: 22-11-2013
Epoch-by-Epoch Ambiguity Resolution for Real-Time Attitude Determination Using a GPS Multiantenna System
Publisher: Institute of Navigation
Date: 06-1995
A review of system integration and current integrity monitoring methods for positioning in intelligent transport systems
Publisher: Institution of Engineering and Technology (IET)
Date: 27-11-2020
DOI: 10.1049/ITR2.12003
Slow Slip Events Associated with Seismic Activity in the Hikurangi Subduction Zone, New Zealand, from 2019 to 2022
Publisher: MDPI AG
Date: 29-09-2023
DOI: 10.3390/RS15194767
Diagnostic Tools Using a Multi-Constellation Single-Receiver Single-Satellite Data Validation Method
Publisher: Cambridge University Press (CUP)
Date: 13-08-2014
DOI: 10.1017/S0373463314000526
Abstract: The use of single-receiver single-satellite data validation parameters for numerical and graphical diagnostics of the multi-frequency observations is presented. This method validates Global Navigation Satellite System (GNSS) measurements of a single receiver where data from each satellite are independently processed using a geometry-free observation model with a reparameterised form of the unknowns. The method is applicable to any GNSS with any number of frequencies. The diagnostic tools are based on checking agreement of characteristics of the validation test statistics against theory. The use of these diagnostics in static and kinematic modes is demonstrated using multiple-frequency data from three GNSS constellations Global Positioning System (GPS), Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS) and Galileo.
Real-Time Precise Point Positioning Using Orbit and Clock Corrections as Quasi-Observations for Improved Detection of Faults
Publisher: Cambridge University Press (CUP)
Date: 05-02-2018
DOI: 10.1017/S0373463317001023
Abstract: Real-time Precise Point Positioning (PPP) relies on the use of accurate satellite orbit and clock corrections. If these corrections contain large errors or faults, either from the system or by meaconing, they will adversely affect positioning. Therefore, such faults have to be detected and excluded. In traditional PPP, measurements that have faulty corrections are typically excluded as they are merged together. In this contribution, a new PPP model that encompasses the orbit and clock corrections as quasi-observations is presented such that they undergo the fault detection and exclusion process separate from the observations. This enables the use of measurements that have faulty corrections along with predicted values of these corrections in place of the excluded ones. Moreover, the proposed approach allows for inclusion of the complete stochastic information of the corrections. To facilitate modelling of the orbit and clock corrections as quasi-observations, International Global Navigation Satellite System Service (IGS) real-time corrections were characterised over a six-month period. The proposed method is validated and its benefits are demonstrated at two sites using three days of data.
LEO Satellite Clock Modeling and Its Benefits for LEO Kinematic POD
Publisher: MDPI AG
Date: 16-06-2023
DOI: 10.3390/RS15123149
Abstract: High-accuracy Low Earth Orbit (LEO) satellite clock and orbital products are preconditions to realize LEO augmentation for high-accuracy GNSS-based positioning on the ground. There is a high correlation between the orbit and clock parameters in the kinematic Precise Orbit Determination (POD) process. While future LEO satellites are planned to be equipped with better clocks, the benefits of modeling high-stability LEO satellite clocks are not yet thoroughly investigated, particularly when mid- to long-term systematic effects induced by the complex LEO relativistic effects and the external environment remain in the clocks. Through clock modeling, this study attempts to reduce not only the short-term noise of radial kinematic orbits, but also mis-modeled effects caused by, e.g., real-time GNSS orbital and clock errors. To explore the benefits of clock modeling, the clocks need to be first detrended by the mid- to long-term systematic effects. While over-detrending limits the orbital improvements, weak detrending would also h er strong clock modeling and easily lead to performance degradations. A balance between the strengths of the detrending and the model thus needs to be investigated for different clock types. In this study, the Piece-Wise Linear (PWL) model of different time lengths and a 2.5-state filter with different strengths (h values) are tested using real data from GRACE FO-1 with an Ultra-Stable Oscillator (USO) on board. Using the CNES real-time GPS products, it was found that when detrending the clocks with a smoothing window of 300 to 500 s, one could generally expect an improvement larger than 10% in the estimation of radial orbits when applying a PWL model with a length from 300 to 1200 s. Improvements of this size can also be expected when using the 2.5-state model with h−1 (for Flicker Frequency Noise) from 10−28 to 10−30.
Improved Coordinate Transformation in Dubai Using a New Interpolation Approach of Coordinate Differences
Publisher: Informa UK Limited
Date: 2009
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