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Satellite position sensing service aims to serve pipeline industry.

Satellite navigation has become a tried and tested surveying tool for energy utilities and grid operators. Satellite positioning systems can record the most important position and elevation coordinates. Operators usually use mobile satellite positioning systems in combination with geographic information systems (GIS) for the initial measurement of their gas grids, choosing pipeline routes, checking cadastral points, and determining the spatial location of system components.

Using mobile satellite positioning/GIS, a single employee can define all necessary positions. Employing mobile satellite positioning/ GIS for recording and accessing survey data in the field also allows various in-house work processes to be handled by field staff.

Satellite Systems

The speed and accuracy with which a satellite navigation system determines a particular position depends on the satellite constellation. The system requires undisturbed signals from at least four satellites simultaneously in order to unequivocally calculate the position from the transit times of the signals.

Today there are two global navigation satellite systems providing signals: the U.S. GPS system with 28 satellites and the Russian GLONASS system with 15 satellites which will be expanded to 24 by 2010. Both systems are collectively referred to as GNSS (Global Navigation Satellite System).

With GNSS technology, however, coordinates can only be determined with a maximum accuracy of 10-30 meters because the signals are often affected by atmospheric disturbances and local interference. To improve accuracy, service providers such as ascos--satellite positioning services, the satellite reference service of E.ON Ruhrgas AG--provide users of satellite positioning systems in Germany with correction data.

This involves taking the inaccurate raw data made available to calculate correction data using a precise network of reference stations, and transferring the correction data by radio link in real time back to the user. The correction allows the main signal errors such as clock, track or runtime errors to be corrected. This method, known as D-GNSS (Differential GNSS) enables accuracies of up to 2 cm where GNSS signals are used.

What cannot be corrected, however, are other shortcomings of the GPS and GLONASS technology: Civil users are not automatically informed by integrity signals if signal transmission is flawed. Moreover, since satellite density (availability) can at times be low, the receipt of signals particularly in inner-city areas and higher altitudes can be very patchy.

Since both GPS and GLONASS are financed and controlled by the military, they are prone to deliberate interference or even the shutdown of their civil use. Moreover, the system operators provide no warranty and cannot be held liable despite the fact that signal integrity/availability and operator liability are key to security-critical applications in many civil areas such as aviation.

New Galileo Service

The European Union decided in 2002 to set up its own commercial satellite navigation service-Galileo--to overcome the existing flaws and open up new areas of application. The system will be operated by a privately owned licensee. The operators will warrant a certain signal quality and availability and be liable to users of security-critical applications. The licensee will receive the marketing rights to the system for 20 years in return for providing most of the project funds.

In December 2005, GIOVE A, the first test satellite, was launched into orbit to secure use of the frequencies allocated by the United Nations. From around 2010 onward, 30 Galileo satellites will be orbiting the earth in a medium-earth orbit (MEO) in three orbit planes at a height of 23,616 km. The satellites will transmit signals worldwide for different public and private commercial services and user groups. Six to eight satellites will be visible at most locations so, unlike GPS, the system guarantees signal reception even in the Northern Hemisphere right up to the polar region.

As Galileo, GPS and GLONASS will be interoperable, users of GPS/GLONASS/ Galileo receiver combinations will eventually have access to some 80 satellites.

Energy Industry Uses

The EU's Galileo integrated georeference applications project (GIGA project) has been looking into additional optimization potential and possible applications for energy utilities and grid operators. The project is being carried out under the leadership of E.ON Ruhrgas by a team of six companies with specific know-how in various technological fields.

The GIGA consortium has examined market opportunities for GNSS and Galileo in the gas, oil and electric industries. The team has conducted a survey among network operators and surveying companies in Germany, Austria, Belgium, Italy, the Netherlands and the UK.

The survey revealed that there are currently four main areas of application, the first one being routine inspections and first-time digital recording of existing lines, followed by grid expansions, modifications and maintenance work.

Leak Surveys

Routine inspections usually involve field crews walking along the line using a gas detector to find any leaks. Throughout the EU, there are around 3,000 of these groups inspecting seven to 20 km of pipeline every day, thus covering 110% of the grids annually. Initial measurement with digital tools is seen as offering substantial potential until 2010 because some 30% of the grids still have to be entered into digital map systems. This means there are still some 400,000 km of grids to be recorded. A field crew usually needs one day to measure a single kilometer.

About half of this surveying work is being done using satellite positioning systems. According to the respondents, this figure is expected to increase to 60% by 2010, 80% by 2015 and, ultimately, even 90% by 2020. Yet, it is unlikely that GNSS will become the only tool used because topographic factors such as shadowing in urban areas and forests do not allow conventional surveying methods to be entirely replaced.

A new, civil satellite positioning system such as Galileo is generally viewed positively. Factors favoring the use of Galileo include improved satellite signal availability, higher signal integrity and lower signal interference than with GPS or GLONASS, better positioning accuracy at elevated locations, the savings potential associated with the use of GNSS, improvements in communication technology and increased legal certainty through GNSS-based surveying and documentation.

Optimization

To examine the technical feasibility of Galileo applications in the energy industry, the consortium conducted a number of studies on Galileo signal transmission and processing.

The first study, entitled "Synergies Between GNSS And Mobile Networks," showed that existing mobile networks which, because of their insufficient accuracy and availability are unsuited for positioning purposes in utility networks, can be used as a low-cost option to supplement Galileo's premium services. Wireless technologies such as Wi-Fi (IEE 802.11), WiMAX (IEE 802.16) or mesh (peer-to-peer) networks, however, can be used as a backup for special applications.

The study entitled "GNSS Receiver And Service Centre Technology," was supposed to show what additional Galileo service benefits there are for the user in comparison to existing GNSS services. As part of its findings, the study proposes a so-called reverse DGNSS system. Reverse DGNSS systems, which use a service center to calculate the positions, allow signal or positioning errors to be detected. The user is informed accordingly by additional integrity data. This significantly improves interaction between a service center and the GNSS receivers over existing GNSS applications.

The study entitled "Harmonized Dissemination Concepts," looked at the suitability of different formats and ways of transmitting positioning and reference data. It showed that the Internet-based NTRIP (Networked Transport of RTCM via Internet Protocol) standard can also be used to safely transmit huge data volumes and different data formats to a large number of users. This makes the NTRIP standard a suitable medium for real-time correction data transmission.

Galileo Service Center

The results of the studies were used to develop the architecture of a Galileo service center in the form of a functional model (demonstrator), which recently passed its final tests. The model offers all functions required for presenting real-life examples of future Galileo services.

The demonstrator simulates a conventional and a reverse DGNSS system as used with Galileo, comprising, on the one hand, the usual service centre components for recording, calculating and transmitting raw and correction data, and, on the other hand, a rover component for receiving and visualizing this information. The components will be integrated into the existing reference network of ascos, the satellite reference service of E.ON Ruhrgas AG.

The key component for visualizing the future functionality and the signal quality of Galileo is an additional QoS (Quality of Service) server, which provides a qualitative assessment of the positioning data along with integrity information. For this purpose, the QoS server receives information from different sources on possible atmospheric interference and on mobile network quality. Using a SISNet interface, EGNOS (European Geostationary Navigation Overlay Service), the precursor of Galileo, also draws on satellite signal quality data for the assessment.

For test purposes and to demonstrate the functional model, special rovers deployed in areas of different topography (forests, urban areas, open country) collect the raw data for transmission to the demonstrator. The raw data are used to calculate precise coordinates which are then made available to the user together with additional integrity and quality information. This makes it possible to show the benefits and improvements of future Galileo services.

Frank Dietzsch is GIGA Prefect Manager for E.ON Ruhrgas AG. headquartered in Germany.

(Editor's Note: Opinions expressed in this article are those of the author and do not necessarily express the views of the staff of Pipeline & Gas Journal.)

By Frank Dietzsch, E.ON Ruhrgas AG, Germany
COPYRIGHT 2007 Oildom Publishing Company of Texas, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2007 Gale, Cengage Learning. All rights reserved.

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Title Annotation:AIRBORNE LEAK DETECTORS
Author:Dietzsch, Frank
Publication:Pipeline & Gas Journal
Geographic Code:4EUGE
Date:Mar 1, 2007
Words:1557
Previous Article:2007 NAPCA member roster.
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