New Developments in River Level Monitoring using GPS Heighting

Terry Moore, Gethin Roberts, Theo Veneboer, Michael Pattinson, Gareth Close and Roger Moore

Abstract:	This paper describes the second phase of the RiGHt project "River Level Monitoring using GPS Heighting". This project was completed earlier this year by a consortium comprising Science System (Space) Ltd, the University of Nottingham and the Centre for Ecology and Hydrology, and was funded by the British National Space Centre (BNSC), under the UK Government’s Space Foresight Programme. The original RiGHt project, which ran for two years, was successful in demonstrating the feasibility of measuring and monitoring river heights using a GPS equipped buoy in a real-time environment and using satellite communications technology to transfer the data to a central and remote Geographical Information System. The aim of RiGHt has been to demonstrate innovation in the integration of state-of-the-art technologies such as OTF GPS and low power world-wide satellite communications to solve a real user need. The objectives of the second phase were to address three key developments to the original architecture. Firstly, the use of long-range kinematic GPS techniques was implemented, so as to extend the useful range of the system. Secondly, long-range use requires the adoption of satellite communication techniques to relay the raw data between the buoy, other reference GPS stations and a central computational hub. This has required the use of advanced data compression techniques, to handle the high data rates necessary for raw GPS carrier phase data. The third objective was to integrate the resulting real-time measures of river level into river and flood modelling software, so as to greatly enhance the benefit of the monitoring to the users. The initial RiGHt project provided the starting point for the research outlined in this paper. In the first phase a precision of 6mm was achieved in real-time during trials on the River Trent. This was accomplished using Real Time Kinematic (RTK) GPS. Although this technique is now used almost routinely for surveying purposes, there is often the requirement of needing a surveyed GPS reference station within line of sight of the ‘mobile’ unit where precise measurements are required. This is not generally been a significant problem when surveying, but was clearly identified as a significant limitation of the original RiGHt system. The need for local GPS reference stations can cause a severe restriction if one is planning to deploy the buoy in a true riverine environment. The Institute of Engineering Surveying and Space Geodesy (IESSG) at the University of Nottingham has previously conducted research into the use of long- range RTK GPS where the reference stations are separated form the mobile unit by distances of 100km or more. This approach has now been integrated in the new RiGHt system. In addition to the buoy based receiver a network of multiple GPS reference stations are used, and all the data is communicated to a central hub where it is collated and processed in near real- time. Previously the link between the buoy and the reference station was achieved using a dedicated radio modem or hard-wire link. In addition, a low-data rate link between the reference station and the central was demonstrated using terrestrial and satellite based packet radio networks. However, when the reference stations are separated from the buoy by distances of 100km or more and when potentially many buoys could be involved, the dedicated link is no longer feasible and a long-range high data-rate link becomes necessary. Science Systems (Space) Ltd. (SSSL) have been involved with terrestrial broadcasting, satellite data communications and data compression for many years. Innovative and reliable data compression and communication techniques have been developed and implemented for RiGHt to meet the ambitious goal of real-time network-based long-range kinematic GPS. Both terrestrial and satellite based communications from the buoy and the reference stations have been implemented and tested throughout the development of the new RiGHt system. In the initial RiGHt project, the water level data was transferred to a central facility where it was stored in a database and displayed using existing data presentation packages in real-time. Level data become infinitely more valuable if they are stored alongside other data sets such as rainfall, water quality, terrain, river channel geometry, geology and soils in a way that makes them accessible by models. They can then be used for real-time flood and pollution forecasting. Hydrological data also become more valuable as the length of record builds up. The history can be analysed to identify trends and trends and risks. The Centre for Ecology and Hydrology (CEH) has many years of experience in the use of hydrological data, the design of environmental databases and the use of this data in flood forecasting. In this phase of RiGHt, the Centre has extended its work to allow the capture of real-time river level data into existing river and flood modelling software packages. This enables RiGHt to provide a complete solution to user needs, rather than simply providing a sensor of river levels. The development of the new RiGHt system was completed by early 2002, and in March a series of land and river based trials were conducted. This paper addresses these significant developments to the RiGHt system, and presents the results from the new series of trials.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	1819 - 1826
Cite this article:	Moore, Terry, Roberts, Gethin, Veneboer, Theo, Pattinson, Michael, Close, Gareth, Moore, Roger, "New Developments in River Level Monitoring using GPS Heighting," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 1819-1826.
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