Network-based RTK Positioning: Impact of Separating Dispersive and Non-dispersive Components on User-side Processing Strategy

The concept of network-based positioning has been extensively developed in order to better model the distance-dependent errors of GPS carrier-phase measurements. These errors can be separated into a frequency-dependent or dispersive component (e.g. the ionospheric delay) and a non-dispersive component (e.g. the tropospheric delay and orbit biases). In fact, dispersive and non-dispersive errors have different dynamic effects on the GPS network corrections. The separation of the two is useful for modelling the network corrections and can provide network users with more options for their data processing strategy. A simple running average is proposed in this paper to provide a stable network correction for the non-dispersive term. It is found that the non-dispersive correction can be used to obtain better ionosphere-free measurements, and therefore helpful in resolving the long-range integer ambiguity of the GPS carrier-phase measurements. Once the integer ambiguities have been resolved, dispersive and non-dispersive corrections can be applied to the fixed carrier-phase measurements for positioning step so as to improve the accuracy of the estimated coordinates. Instantaneous positioning, i.e. single-epoch positioning, has been tested for two regional networks: Sydney Network (SYDNET) and Singapore Integrated Multiple Reference Station (SIMRSN), Singapore. The test results have shown that the proposed strategy performs well in generating the network corrections, in fixing ambiguities and in computing a user’s position

GPS network-based approach to mitigate residual tropospheric delay in low latitude areas

A strong spatio-temporal variation of the wet component in the troposphere leaves us in a peculiar predicament. The residual tropospheric delay will remain in the measurements and therefore affect the estimation of related parameters. In the areas of hot and wet climate conditions, especially in the equatorial or low latitude regions, the strong tropospheric effect on GPS measurements is unquestionable. This study proposes geometric modeling through the network-based approach to mitigate the residual tropospheric delay in such regions. A part of Southeast Asia is selected as a test area for the study, which covers Malaysia and Singapore. Tests are conducted in post-processing but in the “simulating RTK� mode, and evaluated by the number of ambiguity fixes and the accuracy of the coordinate results. Network-based RTK positioning in low latitude areas has shown that the proposed technique can enhance ambiguity resolution by pivoting the ionosphere-free measurements through the mitigated residual tropospheric delay

Stochastic modelling for network-based GPS positioning

Over the past few years the concept of network-based positioning has been developed in support of longer baseline processing compared with 'traditional' single reference station positioning. In fact network-based positioning enables the generation of so-called ‘virtual measurements’, which can significantly improve positioning results. Even though the virtual measurements are generated from the stochastic network estimates, the error propagation into the user position solution has not been investigated in any detail. The aim is to understand how the unique stochastic properties of the network corrections propagate into the uncertainties of the estimated parameters. Test results indicate that by using the virtual measurements and considering the propagation of the network stochastic properties can provide reliable results, both in terms of ambiguity resolution and baseline component estimation

Spatial and seasonal ionospheric error growth in DGPS measurement: a case study in Malaysia

This paper tackles the Equatorial ionosphere and its effects on Differential Global Positioning System (DGPS) error growth over Malaysia by using a network of GPS Continuously Operating Reference Stations (CORS). Seasonal variation of ionospheric delay has been examined and findings show that the effect of spatial variation of ionospheric errors in DGPS is very significant during the equinoctial seasons. Furthermore, a DGPS regression model was developed and tested during the solar maximum year in 2013 by using internet-based DGPS. The results show that the model is capable of estimating DGPS positional errors for distances of user to reference station less than 680 km

Application of Running Average Function to Non-Dispersive Errors of Network-Based Real-Time Kinematic Positioning

The GPS errors can be separated into a frequency-dependent or dispersive component (e.g. the ionospheric delay) and a non-dispersive component (e.g. the tropospheric delay and orbit biases). Dispersive and non-dispersive errors have different dynamic effects on the GPS network corrections. The former exhibits rapid changes with high variations due to the effect of free electrons in the ionosphere, whilst the latter change slowly and smoothly over time due to the characteristic behaviour of the tropospheric delay and the nature of orbit biases. It is found that the non-dispersive correction can be used to obtain better ionosphere-free measurements, and therefore helpful in resolving the long-range integer ambiguity of the GPS carrier-phase measurements. A running average is proposed in this paper to provide a stable network correction for the non-dispersive term. Once the integer ambiguities have been resolved, both dispersive and non-dispersive corrections can be applied to the fixed carrier-phase measurements for positioning step so as to improve the accuracy of the estimated coordinates. Instantaneous positioning i.e. single-epoch positioning, has been tested for two regional networks: SydNET, Sydney, and SIMRSN, Singapore. The test results have shown that the proposed strategy performs well in generating the network corrections, fixing ambiguities and computing a user’s position

Low latitude troposphere: a preliminary study using GPS CORS data in South East Asia

Hot and wet conditions in the equatorial or low latitude region degrade satellite positioning accuracy noticeably. The degradation is related to the strong tropospheric effect, especially the wet component which is approximately proportional to the content of water vapor in the troposphere and thus makes satellite positioning more challenging in this region. Despite the efforts to achieve better understanding of the signal delay in the low latitude troposphere, much more still remains to be improved. Knowing that the water vapor content is heavy in this region, it is of special interest for meteorologists to look into the tropospheric effect. Such knowledge is vital for understanding the global climate, whereas a short term variation of water vapor is very useful input to local weather forecasting. South-East Asia is selected in this study to investigate the effect of regional tropospheric delay, and broadly to understand the behavior of a low latitude troposphere. The study area covers Malaysia and Singapore where GPS CORS networks have already been established. Results from GPS data processing show that a wide variation of the tropospheric delay can be observed. As expected, the largest variation occurs during the North-East monsoon (November to early March) and the South-West monsoon (early May to August). Coordinate repeatabilities of the sites in the network are calculated to show the impact of the tropospheric delay on the precision of GPS positioning activities. In addition, the variations of the tropospheric delay estimated from a local and a regional GPS network are compared to the results from the global network

Pergau Reservoir Information System (PRIS) for mapping and sedimentaion studies: A study on the development of the reservoir database

The main part of a hydroelectric project is the dam with its natural or man made lakes or reservoirs. As in the case of many tropical countries, heavy rainfally and effects of upstream changes in landuse have caused detrimental consequences on the sedimentation. Reservoir Information system, therefore, is recognized presetly as the most suitable and efficient tool to manage the reservoir. The present study will focus on Reservoir Information system for the Pergau Hydroelectric Project, which is located in the State of Kelantan, Malaysia. This paper presents the results of the first phase of the study, i.e. on the data sources and data acquisition techniques in order to develop the Pergau Reservoir Database. The Database will be the major component part of the Pergau Reservoier Information System (PRIS)

Mitigating Residual Tropospheric Delay to Improve User’s Network-Based Positioning

Existing apriori tropospheric models are not sufficiently accurate to remove tropospheric delay from GPS observations. Remaining effects of residual tropospheric delay need to be estimated to ensure high accuracy and reliability of GPS positioning. Other researchers have shown that implementations of network-based positioning techniques can adequately model the residual tropospheric delay as well as ionospheric delay and orbit biases. However, the effectiveness in removing residual tropospheric delay is highly dependent on the degree to which the wet component from the troposphere can be estimated or mitigated, an effect which shows strong variation with time and space. The aim of this paper is to illustrate the performance of an existing apriori tropospheric model and to discuss some issues concerning the estimation of the (total) tropospheric delay in the equatorial area. Finally, the network approach is applied to mitigate the effect of residual tropospheric delay. Some preliminary results from test experiments using GPS network data from an equatorial region, a location with the highest effect of tropospheric delay, are presented

Penentudukan Titik dan Ketinggian Ortometrik Menggunakan Data GPS: Integrasi Perisian GPPS dan L3D-HEIGHT

Di dalam kerja penentududukan stesen di bumi dan penentuan ketinggian menggunakan data satelit GPS, beberapa langkah pemprosesan data perlu dilakukan. Data cerapan yang dikutip oleh alat penerima GPS di padang perlu diproses dahulu sebelum digunakan di dalam suatu pelarasan jaringan geodetik untuk mendapatkan nilai koordinat setiap stesen yang telah diduduki alat penerima. Antara perisian yang boleh digunakan bagi pra-pemprosesan ialah GPPSâ„¢. Hasil dari pra-pemprosesan kemudiannya digunakan di dalam satu perisian pelarasan jaringan geodetik seperti L3D-HEIGHT. Masalah timbul apabila terdapat ketidakserasian di antara hasil keluaran GPPSâ„¢ dan format masukan cerapan L3D-HEIGHT. Kertaskerja ini membentangkan langkah-langkah yang diambil serta perisian yang telah dihasilkan bagi mengatasi masalah tersebut

Analysis of residual atmospheric delay in the low latitude regions using network-based GPS positioning

The atmosphere in low latitude regions is of particular interest to GPS researchers because the propagation of GPS signals becomes significantly delayed compared with other regions of the world. Hence this limits GPS positioning accuracy in equatorial regions. Although the atmospheric delay can be modelled, a residual component will still remain. Reducing, or mitigating the effect of residual atmospheric delay is of great interest, and remains a challenge, especially in equatorial regions. Analysis of relative positioning accuracy of GPS baselines has confirmed that the residual atmospheric delay is distance-dependent, even in low latitude areas. Residual ionospheric delay is the largest component in terms of both absolute magnitude and variability. However it can be largely eliminated by forming the ionosphere-free combination of measurements made on two frequencies. The residual tropospheric delay is smaller in magnitude but rather problematic due to strong spatio-temporal variations of its wet component. Introducing additional troposphere “scale factors� in the least squares estimation of relative position can reduce the effect of the residual. In a local GPS network, the distance-dependent errors can be spatially modelled by network-based positioning. The network-based technique generates a network “correction� for user positioning. The strategy is to partition this network correction into dispersive and non-dispersive components. The latter can be smoothed in order to enhance the ionosphere-free combination, and can be of benefit to ambiguity resolution. After this step, both the dispersive and non-dispersive correction components can be used in the final positioning step. Additional investigations are conducted for stochastic modelling of network-based positioning. Based on the least squares residuals, the variance-covariance estimation technique can be adapted to static network-based positioning. Moreover, a two-step procedure can be employed to deal with the temporal correlation in the measurements. Test results on GPS networks in low latitude and mid-latitude areas have demonstrated that the proposed network-based positioning strategy works reasonably well in resolving the ambiguities, assisting the ambiguity validation process and in computing the user’s position. Furthermore, test results of stochastic modelling in various GPS networks suggests that there are improvements in validating the ambiguity resolution results and handling the temporal correlation, although the positioning result do not differ compared to using the simple stochastic model typically used in standard baseline processing