Use Of Differential GPS Research Articles

Radio-frequency sensor fusion for relative navigation of formation flying satellites

The increasing need for robustness, reliability and flexibility of relative navigation systems imposed by the current and future autonomous formation flying missions, calls for the implementation of solutions using an alternative approach to single-sensor systems. These schemes possess different levels of availability, mainly driven by sensor failure and mission orbit profiles. The data obtained from the global positioning system (GPS) and formation flying radio-frequency (FFRF) sensors from the nominal phase of the PRISMA mission provide an opportunity for the implementation of an extended approach for the generation of relative navigation solutions. The present study introduces the design of a simple relative navigation filter based on the sensor fusion concept, which makes use of differential GPS and FFRF measurements obtained from the on-board sensors. The filter design uses the Hill-Clohessy-Wiltshire and Yamanaka-Ankersen relative dynamics models as well as numerical integration methods including the J2-perturbation for the state and associated covariance matrix propagation. The design is tested using flight data obtained during representative formation flying operations of the PRISMA mission.

Análise da influência vegetacional na altimetria dos dados SRTM em bacias hidrográficas no semiárido

A topografia evidencia-se como um fator imprescindível no entendimento da dinâmica hidrológica e ambiental. Assim, torna-se fundamental a validação de dados altimétricos obtidos por sensoriamento remoto. Os dados SRTM de elevação são resultado de uma missão orbital por RADAR interferométrico que corresponde à topografia da superfície da Terra, considerando inclusive a influência da vegetação no retorno do sinal. O objetivo deste trabalho é validar os dados SRTM para as condições do semi-árido brasileiro. Para isto foram elaboradas comparações e análise estatística de dados obtidos no campo com GPS diferencial e outras bases de dados referenciais existentes, cartas planialtimétricas DSG/ SUDENE e dados de RN do IBGE em pontos localizados na bacia do rio Jaguaribe situada no semi-árido cearense. Os resultados apresentaram erro altimétrico de aproximadamente 7,0 m com relação aos RNs da bacia. Com uso do DGPS em um relevo plano com baixa declividade e com vegetação de porte baixo os resultados apontam um erro altimétrico de aproximadamente 1,7 m. Conclui-se que, apesar da influência da cobertura vegetal na variação altimétrica, os dados SRTM apresentam-se confiáveis para regiões com vegetação típica do semi-árido.

Mapping and analysing medieval built form using GPS and GIS

Drawing upon recent research experiences of using a Global Positioning System (GPS) and Geographical Information Systems (GIS), this paper sets out how spatial technologies can be used in the study of medieval built form. The paper focuses particularly on the use of differential GPS and ArcGIS in mapping and analysing the plan of Winchelsea, an English medieval 'new town' established in the 1280s. The approach used to conduct this research is outlined here, with comments on the practicalities of using GPS and GIS in historical urban morphology. Although the research on which this paper is based is at a preliminary stage, the paper offers a working method for those interested in using spatial technologies to build upon existing methods of morphological study, namely town-plan analysis and metrological analysis. Some preliminary research findings relating to the planning of medieval Winchelsea are also presented.

Friction Estimation on Highway Vehicles Using Longitudinal Measurements

This paper develops a real-time tire-road friction coefficient measurement system that can reliably distinguish between different road surface friction levels and quickly detect abrupt changes in friction coefficient. The measurement system relies on the use of differential GPS and utilizes a nonlinear longitudinal tire force model. Compared to previously published results in literature, the advantage of the system developed in this paper is that it is applicable during both vehicle acceleration and braking and works reliably for a wide range of slip ratios, including high slip conditions. The system can be utilized on front/rear-wheel drive as well as all-wheel drive vehicles. Extensive results are presented from experimental results conducted on various surfaces with a winter maintenance vehicle called the “SAFEPLOW.” The experimental results show that the system performs reliably and quickly in estimating friction coefficient on different road surfaces during various vehicle maneuvers. The developed friction measurement system has many applications in vehicle safety systems such as ABS, skid control and collision avoidance systems and is also useful for winter maintenance vehicles in which knowledge of the friction coefficient can be used to determine the amount and type of deicing chemicals to be applied to a winter roadway.

Experimental Study on Application of DGPS-based Position Information to Automatic Driving Control

Experimental studies are conducted for investigating the possibility of automatic driving control systems based on absolute position information. Implementation of such control system requires a methodology of measuring the absolute position, and a control algorithm. In this paper, an accurate and real-time estimation of the absolute position by use of DGPS (Differential Global Positioning System) and sensors on a controlled vehicle is proposed. Automatic steering controller, automatic evasive controller, and a method of relative position measurement of neighboring vehicles are also proposed as application of position information to automatic driving control. Experiments are conducted using sedan-type vehicles. Experimental results validate the proposed estimation and control system, and provide the perspective of enhancing the automatic driving control system by use of the absolute position information.

Differential GPS-Based Position Measurement and Steering Control for Automatic Driving.

Simulation and experimental studies are carried out for investigating the possibility of automatic vehicle control system based on absolute position information. Implementation of such control system requires a methodology of measuring the absolute position, and a control algorithm. An accurate and real time measurement of the absolute position by use of DGPS (Differential Global Positioning System) and sensors on a controlled vehicle is proposed. A steering control algorithm for tracking the desired course stored as absolute position data is also proposed. Simulation and experimental results validates the proposed measurement and control system, and provides the perspective of enhancing the automatic driving control system by use of the absolute position information.

A geographic information system applied to a malaria field study in western Kenya.

This paper describes use of the global positioning system (GPS) in differential mode (DGPS) to obtain highly accurate longitudes, latitudes, and altitudes of 1,169 houses, 15 schools, 40 churches, four health care centers, 48 major mosquito breeding sites, 10 borehole wells, seven shopping areas, major roads, streams, the shore of Lake Victoria, and other geographic features of interest associated with a longitudinal study of malaria in 15 villages in western Kenya. The area mapped encompassed approximately 70 km2 and included 42.0 km of roads, 54.3 km of streams, and 15.0 km of lake shore. Location data were entered into a geographic information system for map production and linkage with various databases for spatial analyses. Spatial analyses using parasitologic and entomologic data are presented as examples. Background information on DGPS is presented along with estimates of effort and expense to produce the map information.

GPS and Differential GPS Integrity Monitoring

The problem of Global Positioning System (GPS) and differential GPS (DGPS) integrity monitoring is discussed. The use of DGPS for navigation-critical marine applications (for example, harbor crossing) requires the navigation signals integrity monitoring. Integrity monitoring consists of two functions: detection of the fact that a navigation satellite produced wrong data; isolation or identification of which DGPS channel (satellite) is malfunctioning. The paper describes a new optimal statistical approach to these problems.

Some considerations and developments to the operational use of differential GPS in Marine Geodesy

Two different types of differential global positioning systems (DGPS) are used for precise positioning and navigation. The “ordinary”; DGPS combines range corrections from a reference station with carrier smoothed pseudoranges at the moving station. This method works on a routine basis and provides accuracies of down to I m or even less. The precise differential GPS concept (PDGPS) uses carrier phase observations of both stations and requires an ambiguity resolution while the user platform is moving. This technique provides accuracies of 0.1 m or less, but it is much more difficult to realize. Within this paper both concepts are discussed and presented in examples. In particular, the limitations and chances of the PDGPS technique and the possibility of its operational use are critically investigated.

Advances and Test Results in Differential GPS Navigation

The concept of differential GPS has been under study, test and refinement for about 10 years. Operational use of differential GPS is now practical, effective and highly reliable. Refinements to the concept of differential GPS have evolved over this period, several of which have been reported by Trimble Navigation personnel. It is now reasonable to conclude that the ‘second generation’ of differential GPS has arrived, with a collection of technical improvements and features that make its use even more accurate, robust and reliable.

Differential GPS: Efficient Tool in Photogrammetry

In the photogrammetric mapping process, a reduction of the amount of ground control can be realized when the position of the aerial camera, or to be more precise the position of its projection center, is determined during the flight. In this paper the results of a testflight performed to investigate the use of differential GPS for this position determination are discussed. From a testfield with extensive ground control, 360 photographs were taken in twelve different strips. Using two different photogrammetric block-adjustment methods, the coordinates of the projection centers were determined for two different block-configurations.

AN INTELLIGENT AUTOMATIC GUIDANCE SYSTEM FOR SURFACE SHIPS

For the European maritime industry to retain an edge over its competitors, it must provide a cheap cost effective, efficient service to the customer. In providing such a service safety levels cannot be compromised and indeed should be enhanced. It is a false economy to employ poorly trained crews on ill-equipped ships as such operations carry increased risk of accidents, collisions and equipment failure, and frequently leads to loss of life and damage to the environment. The only realistic solution, as some industrial nations have realised, is to gain competitive edge by exploiting current and future technology to its full extent. This paper considers the possibility of a fully automatic intelligent integrated ship guidance system that is able to track, with a high degree of accuracy, a pre-defined state trajectory. Built within the system is the ability to make decisions when there is a potential hazard on its predetermined route, and take, automatically, with due regard to international regulations, corrective action. This paper reviews the current state of hardware and software and demonstrates, using highly accurate simulation models of surface vessels, the feasibility of such a system. INTRODUCTION Autopilot Systems Automatic guidance of ships has its origin near the beginning of this century following the invention of the gyrocompass. Traditionally, ship autopilots are single input (desired heading) and single output (actual heading) control systems using generally only a compass as a sensor. Most autopilots employ a proportional, integral and derivative (PID) control law as described by Bech [1]. However, vessel response is sensitive to controller parameter settings, which ideally should be adjusted to cope with changes in environmental conditions such as sea state, or the loading and trim conditions of the vessel. For this reason there have been moves to employ adaptive algorithms to implement selftuning autopilots. Originally these were based on the work of Astrom and Wittenmark [2]. Since the proposition of fuzzy set theory in 1965 by Transactions on the Built Environment vol 11, © 1995 WIT Press, www.witpress.com, ISSN 1743-3509 642 Marine Technology and Transportation Zadeh, there have been numerous applications, including the application of fuzzy sets to ship autopilot design by Sutton and To will [3]. The fundamental problem with conventional autopilots is that they are single dimensional, controlling one parameter only, whereas by its very nature a ship is a multidimensional system with many inputs and outputs which, for complete integrated ship guidance, need to be controlled simultaneously. By the use of multi-variable system theory it is possible to describe the complete motion of a ship and hence formulate an optimal control policy that can view the global problem, and so minimise the errors in the controlled variables according to some predefined order of priority. Optimal guidance systems have been designed and implemented [4] that can provide high accuracy performance for such parameters as position on earth's surface, course and forward velocity control. Navigation Systems Hyperbolic electronic positioning systems such as Omega, Decca and Loran C have been around for some time, but systems such as Decca, although reasonably accurate, do not have world-wide coverage. Satellite navigation has been with us for about twenty years. Although early systems such as Transit have world-wide coverage, continuous position fixes are not available. The recently introduced Global Positioning System (GPS) gives continuous 3-D world-wide navigation coverage, as does the Russian GLONASS satellite navigation system, due to be fully operational by 1995. GPS has an accuracy of 16 m for military users (P code) and 100 m for general users (C/A code). However, there is an increased use of differential GPS, where land-based receivers of known position, transmit errors to local users, thus providing a high level of accuracy. System Integration There have been a number of Ship of the Future projects in recent years [5][6][7j. One of the main conclusions to be drawn from these projects is the need for system integration. The concept of total ship system integration is shown in Figure 1 and requires that all shipboard instruments have a standard interface to a common data highway, communicating using a standard protocol. Such a system currently being developed is the Maritime Information Technology Standard (MITS) being developed by European maritime IT suppliers [8]. SHIP MOTION SIMULATION In order to demonstrate the effectiveness of a fully automatic guidance system, it is necessary to have an accurate dynamic mathematical model of a surface ship, that responds to control inputs (rudder, main engines) and environmental inputs (wind, waves and tide). A realistic six degree of freedom model has been developed to cope with such situations. Transactions on the Built Environment vol 11, © 1995 WIT Press, www.witpress.com, ISSN 1743-3509 Marine Technology and Transportation 643 fl CONTROLS AND NAVIGATION '.••.; : ',.'*•'''''}'''' SHIF EMENT