Land surveying and civil engineering monitoring
Background & Objectives
Europe has a history of natural disasters, such as earthquakes, landslides, floods and volcanic activity. For nearly 50 years, geodesists and surveyors have developed deformation-monitoring techniques based on traditional land surveying equipment, such as theodolites, EDMs and levels. From the 1980s onwards, these traditional techniques were first supplemented and later completely replaced by satellite positioning technology based on GPS. At the start, the time-related measurement data was collected from the different GPS sensors placed at critical locations on the structure and then post-processed.
Later, these measurements were broadcast to the control centres by using dedicated links, such as short-range radio, fibre optic cables and the Internet for quasi-real-time collection, processing and monitoring. However, on its own, GPS suffers from a number of limitations which affect the coverage, accuracy and reliability of the satellite measurements. The eventual emergence of Galileo and its proposed interoperability with GPS, and the use of EGNOS, will contribute substantially to the quantity and quality of the satellite measurements, thereby improving the quality of the deformation monitoring process. Moreover, the availability of signals from two different satellite systems is likely to reduce the price of GNSS receivers and sensors, thus enabling a wider spatial coverage with an increased number of monitoring points.
Galileo would be an essential tool in several GNSS applications in civil and environmental engineering, especially with regard to monitoring building and bridge movements, landslides, and the position of workers in construction yards so to increase their safety.
The consortium has analysed many applications of GNSS in civil and environmental engineering and in cartography. From among about 25 applications, the consortium has selected three, which were:
- monitoring buildings on landslides
- monitoring bridges
- monitoring the position of construction yard workers and their machines to ensure workers' safety.
These cases became pilot projects, for which a real time monitoring centre facility at Thales Alenia Space has been added. In the first two cases, a network of radio-interlinked L1 GPS receivers has been used. Differential data has been sent to the monitoring centre. Tests have been performed at the Severn Bridge (UK) and at Gaggio Montano (IT), a village subject to landslide. In the construction-yard pilot project, all types of GPS and DGPS receivers have been used for accuracy from 10 metres (trucks and machines positioning when driven towards and away from the yard, for yard organisation) to submetric level (mutual position of workers and machines).
Vehicles equipped with DGPS/INS have been used also. EGNOS has been used for DGPS, when available, or, alternatively, local reference GPS stations have been used. Tests have been done at the Consorzio di Bonifica Valligrandi, Legnago (IT) which is considered to be a large yard by workers' safety legislation and at a small yard in the old town centre of Trieste.
The project objectives are:
- to demonstrate, via pilot projects, the use of GNSS for environmental and civil engineering monitoring;
- to demonstrate, via pilot projects, current satellite positioning technologies and through simulation the added benefits of EGNOS/Galileo;
- to design and realise an operational centre for environmental and assets monitoring;
- to analyse the barriers to the wider penetration of GNSS within the land survey and civil engineering markets, and propose enablers to overcome these barriers covering technology advances, strategy for market penetration and a regulatory framework.
Work performed & results
The experiments have confirmed that Galileo or an equivalent GNSS system has to be added to GPS so as to increase the position availability in civil and environmental engineering applications. No guarantee is possible if only GPS or GPS+GLONASS is used to monitor workers and machines in construction yards. The same is for landslides and building monitoring in deep valleys or in town centres. As confirmation, when GPS is available, as in the test at Valligrandi which is entirely on the River Adige plain, then the GNSS monitoring has been demonstrated as feasible. While the GNSS monitoring of the Severn Bridge suffered only from satellite eclipsing due to its structure, in thousands of other cases it was found that hills and buildings create problems when carrying out GNSS monitoring. Hence more satellites are needed. Moreover, particular features of Galileo, like the 3-band commercial service, could be of general interest in an area which cannot be easily covered by RTCM via GPRS or any wireless data communication system. However, the SIS guarantee by Galileo is succeeding.