Rover Stations Research Articles

Network code DGPS positioning and reliable estimation of position accuracy

A network reference station approach instead of a single reference station improves the efficiency and reliability of precise GPS positioning. GPS reference stations exist in some countries, and GPS observations are available for users in real-time mode and for post-processing. This paper presents DGPS post-processing positioning with the use of three simultaneous reference stations. The paper shows that when a reference station network is used, it can create pseudo-range corrections for a virtual reference station, located in the vicinity of an unknown station, and improve the accuracy of determined positions. Network reference stations give redundant observations and reduce the impact of some measurement errors. Practical calculations and analysis of accuracy in code DGPS positioning and the validation of standard deviations determined from adjustment are presented for medium-long distances between a rover and reference stations.

Static Network Code Dgps Positioning vs. Carrier Phase Single Baseline Solutions for Short Observation time and Medium-Long Distances

Static Network Code Dgps Positioning vs. Carrier Phase Single Baseline Solutions for Short Observation time and Medium-Long DistancesGPS land surveys are usually based on the results of processing GPS carrier phase data. Code or pseudorange observations due to considerations of accuracy requirements and robustness are preferred in navigation and some GIS applications. Generally, the accuracy of that positioning is in the range of about 1-2 meters or so, on average. But the main problem in code GPS positioning is to know how to estimate the real accuracy of DGPS positions. It is not such an easy process in code positioning when one reference station is used. In most commercial software, there are no values of accuracy but only positions are presented. DGPS positions without estimated errors cannot be used for surveying tasks and for most GIS applications due to the fact that every point has to be have accuracy determined. However, when we used static GPS positioning, it is well known that the accuracy is determined, both during baseline processing and next by the adjustment of a GPS network. These steps of validation with redundancy in classical static phase baseline solutions allow wide use of static or rapid static methods in the main land surveying tasks. Although these control steps are commonly used in many major surveying and engineering tasks, they are not always effective in terms of short-observation-time sessions. This paper presents a new network DGPS approach of positioning with the use of at least three reference stations. The approach concerns also valid accuracy estimation based on variance-covariance (VC) matrix in the least-squares (LS) calculations. The presented network DGPS approach has the ability of reliable accuracy estimation. Finally, network DGPS positioning is compared with static baselines solutions where five-min sessions were taken into consideration for two different rover stations. It was shown that in a short observation time of GPS positioning, code network DGPS results can give even centimetre accuracy and can be more reliable than static relative phase positioning where gross errors often happen.

Delay difference between tracking loops of different types or TL with various bandwidths of C/A code in GPS

AbstractIn GPS positioning by code timing, the accuracy of the basic stand‐alone positioning based only on information broadcast from GPS satellites is approximately 10 m (2 drms). But in GPS utilizing the results of observation by a reference station, the error due to the satellite and the channel can be eliminated, resulting in a positioning accuracy of 1 m (2 drms) or less. In applications in which high accuracy is required, although not as high as in carrier positioning, but in which the satellite signal is often interrupted, it is effective to use DGPS based on code timing. In DGPS based on code timing, the information acquired by a single reference station can be utilized by many rover stations. Different trackers are used in the reference and rover stations. This paper considers the DLL (delay lock loop) system, which is widely used in code tracking, and the SCELL (sampled code edge locked loop) system, with different characteristics. The differential error between the reference and rover stations which is caused by the difference in the receiver bandwidth, the satellite transmission bandwidth, and the difference in code numbers, is analyzed. It is shown that by widening the tracker bandwidth, the error is made sufficiently small compared to that obtained in ordinary DGPS. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(2): 91–98, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1186

Accuracy Performance of Virtual Reference Station (VRS) Networks

Recent developments in differential GPS (DGPS) services have concentrated mainly on the reduction of the number of permanent reference stations required to cover a certain area and the extension of the possible ranges between reference and rover stations. Starting from networked DGPS stations where all stations are linked to a central control station for data correction and modeling, the most advanced technique nowadays is based on the virtual reference station (VRS) network concept. In this case, observation data for a non-existing “virtual” station are generated at the control center and transmitted to the rover. This leads to a significant improvement in positioning accuracy over longer distances compared to conventional DGPS networks. This paper summarizes the various DGPS architectures and the corresponding accuracy. This is followed by a description of the models and algorithms used for the VRS station concept. Practical examples of correction data services in Europe are given to highlight the achievable positioning accuracy. The results of an analysis of test data in a virtual reference station network in southern Germany show that always a horizontal positioning accuracy in the order of ± 5 cm can be achieved for baselines with a length up to 35 km.

Internet-Based Real-Time Kinematic Positioning

This article investigates the use of the Internet as the communication link between the base and rover stations for the development of an Internet-based Real-Time Kinematic (RTK) system. An Internet-based RTK system has many advantages if compared to current radio-based RTK systems. To validate the concept, a prototype system has been developed and tested in both static and kinematic modes. The results indicated that the base differential data latency is in the range of about 1 second and the RTK positioning accuracy is at the centimeterl level. © 2002 Wiley Periodicals, Inc.

The Mars-94 and Mars-96 missions

The main goal of Solar System studies in Russia for the next 10-15 years is Mars and the Mars-94 project is the first stage of this long-term space programme. In October 1994 it is planned to launch a spacecraft with the following components onboard: an orbiter, two small autonomous stations to be landed on the surface of Mars and two penetrators to analyse the underlying surface layers. The main scientific objectives of this mission are to investigate the evolution and contemporary physics of Mars, and to make, using various methods, a wide range of comprehensive studies of those physical and chemical processes which took place in the past and which continue there now. The payload of the Mars-94 orbiter includes 23 scientific instruments to study the Martian surface, the inner structure of the planet, its atmosphere, and its plasma envelope, as well as instruments for astrophysical studies. The next stage of the programme is a mission to Mars in 1996. At present the Mars-96 project includes a spacecraft with an orbiter, a Martian rover, a balloon, penetrators and small stations. A short description of the scenario, payload, and scientific objectives of these missions is presented in this paper.