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УДК 528:629.783 Крис Ризос
Университет штата Новый Южный Уэльс, Австралия Джоэль ван Крейненброк Leica Geosystems, Швейцария
ДЕФОРМАЦИОННЫЙ МОНИТОРИНГ С ИСПОЛЬЗОВАНИЕМ ПРИНЦИПОВ «СЕТЬ ГНСС - КИНЕМАТИКА РЕАЛЬНОГО ВРЕМЕНИ»: АНАЛИЗ НОВОГО ПОДХОДА
Chris Rizos
School of Surveying & Spatial Information Systems University of New South Wales, Sydney NSW 2049 Australia
Joel van Cranenbroeck GNSS Networks & Geodetic Monitoring Leica Geosystems Heerbrugg, Switzerland
DEFORMATION MONITORING USING NETWORK-RTK PRINCIPLES: CASE STUDIES OF A NEW APPROACH
Abstract
GNSS technology is being extensively used for monitoring the movement of engineering structures such as bridges, tall buildings, dams, breakwaters, etc. Large structures have many GNSS receivers installed on them, and this trend is expected to continue unabated. Several other trends are also emerging:
1. Integrated deformation monitoring systems, consisting of some or all of the following hardware components: GNSS receivers, optical total stations, digital levels, laser alignment devices, inclinometers, accelerometers, strainmeters, anenometers, meteorological sensors, and others.
2. Real-time kinematic (RTK) being almost exclusively the GNSS technique that is used.
3. The use of low-cost L1-only GNSS sensors on the deforming structure, that simply data stream raw GNSS data to a central facility for processing.
4. Sophisticated system control platforms that link to and manage the data logging and control of many sensors (including GNSS), as well as real-time generation and analysis of resulting displacement time series.
5. Increasing interest in taking advantage of installed GNSS reference station infrastructure, rather than establishing reference stations specifically for the monitoring project.
What is clear is that the RTK-GNSS technology is the core component. There are nevertheless challenges in using GNSS. For example, structures such as bridges may provide few points where the GNSS sensors can have clear sky view, and GNSS coordinate accuracy is vulnerable to satellite geometry (number of visible satellites and their distribution in the sky). Another shortcoming of GNSS is that the accuracy
of the derived vertical (height) coordinate is less accurate than the horizontal components. GNSS is also vulnerable to signal multipath disturbance from the structure itself. However, perhaps the most severe challenge is logistical. RTK-GNSS requires a GNSS reference station located nearby, on a stable reference mark.
The issue of reference stations is particularly problematic for deformation monitoring applications. For example, in built up downtown/urban areas (where tall buildings are located), or rugged natural terrain (typically where long bridges and dams are sited), it may be difficult to setup a stable GNSS reference receiver. This is even more of a challenge if a pre-existing continuously operating reference station (CORS) is to be used. It may be located too far away from the structure being monitored, and hence the GNSS sensor coordinate accuracy will suffer due to baseline length-dependent errors (particularly due to the atmospheric delay, and especially if the GNSS sensor is capable of L1-only tracking).
The use of clusters of CORS to support network-RTK (N-RTK) operations within their area of coverage is now very common. N-RTK is a very viable technique for use as the underlying technological base for regional and local high productivity, real-time, high accuracy services, with less installed CORS infrastructure than would otherwise be necessary if the single-base RTK-GNSS technique were to be used.
In this paper, a new deformation monitoring concept that uses N-RTK principles will be described. Test results from two projects in Hong Kong will be presented to demonstrate the superior results of this implementation of the N-RTK service, using single-frequency GNSS sensors, in a region where the ionospheric refraction effects are large and unpredictable.
© Крис Ризос, Джоэль ван Крейненброк, 2009
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