Utilisation of GNSS for Monitoring Processes

UTILISATION OF GNSS FOR MONITORING PROCESSES :

A PROJECT MANAGER’S PERSPECTIVE

Velan Shanmuga V1, Chakravarty D

1, Chakrabarti P P

2

1 Department of Mining Engineering, Indian Institute of Technology Kharagpur, 721302, India

2Department of Computer Science & Engineering, Indian Institute of Technology Kharagpur, 721302, India

Abstract: This paper presents the advantages of using Global Navigation Satellite System (GNSS) for monitoring of projects. GNSS is one of the most suitable technologies for monitoring. Latest developments in GNSS have increased this suitability. Nine critical factors that are to be considered by the project managers have been selected and analysed. Contrary to general belief, accuracy of the GNSS and their receivers are not constant world over. Each system is optimized for the country or region of its origin and cannot be used directly over the Indian region. The errors also keep varying in the time domain. The solution should not be used when GDOP is optimum. The augmentation system increases accuracy but the selection of the type should be ‘deliberate’ and only suitable system should be: if more than one source of augmentation is available. While using Differential GNSS inputs, accurate and correct positioning of pivot station is vital. The developers of the IT solution are supposed to have in-depth knowledge on GNSS, else, there is a possibility that the developer might naught the GNSS input altogether. It is also better to use Multiple GNSS to overcome the issues of GDOP and satellite availability. A good understanding of the key factors mentioned will enable better project management. Key Words: project management, monitoring processes, GNSS, GPS, monitoring solutions

1 Introduction

Monitoring processes group integrates all other process and is considered as the ‘background’ process group [12]. It involves continuous tracking and evaluation of the project against the timelines. Global Navigation Satellite System (GNSS), better known by the US implementation Global Positioning System (GPS), provides us a good method for such monitoring. Its applications and usefulness in monitoring various projects is well documented [1]. Further, the completion of the GPS modernisation programme in 2010 [13] has given a compelling reason for the project managers to adopt GNSS based monitoring solutions in their projects. However, while adopting this, care should be taken to understand the nuances of the GNSS technology; else the effort will become counterproductive.

There are a number of parameters like required positional accuracy, Geometric Dilution of Precision

(GDOP), No of satellites and algorithms used that affect the overall output of the GNSS solution. Also, there are systems and services, other than the primary system like, augmentation services, differential services, and other GNSS systems. A good understanding of these issues will help the project manager to implement the project successfully in shortest possible time. These aspects are analysed in this paper. 2 Brief description on GNSS and constellations GNSS consists of a set of satellites that circle the globe in medium earth orbits. The position and the orbit of the satellites are chosen such a way that any user in any location on earth should be able to receive the signals of desired quality. The system consists of space segment, user segment and control segment. Space segment encompasses the satellites and their support network, user segment includes the receivers, users and user applications and the control segment consists of a worldwide network of monitoring and control stations. The constellation provides an easy means of locating user position on earth using low cost receiver equipment.

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GPS is the oldest GNSS that is being maintained by USA. Apart from it, there are GLONASS of

Russia, Beidou of China and Galileo of EU. Japan has a regional system called MSAS. India has plans to establish Indian Regional Navigation Satellite Systems (IRNSS) and launched the first satellite IRNSS 1 satellite recently [10].

Apart from the primary systems mentioned in earlier paragraph, there are satellite based

augmentation systems (SBAS). Augmentation systems to GPS are available around the world and are being used for civil aviation by International Civil Aviation Organisation (ICAO). It consists of Wide Area Augmentation System (WAAS) of USA, European Galileo Navigation Overlay System (EGNOS) of EU, GPS Aided Geo Augmented Navigation (GAGAN) of India and Multipurpose Transportation Satellite (MTSAT) Augmentation System (MSAS) of Japan. These systems have satellites that are geo-stationary and transmit signals like GPS satellites. They also transmit error correction parameters that the receivers use to correctly predict the user location. GAGAN is at present in the ICAO acceptance and certification stage. 3 Advantages of using GNSS for Monitoring

The project management body of knowledge (PMBOK) lays down a series of processes to monitor a project. There are many methods / means of monitoring to support these processes. Most of them are active and has human element in the chain. On analyzing all available systems / methods and observing their implementation in various projects over the past decade, the authors have observed that amongst these, the GNSS is the most suitable for monitoring purposes. It enables continuous tracking of elements within the project in real time. The below listed nine critical factors provide a distinct advantage to GNSS:-

(a) Most of the services of the GNSS constellation are free; providing one of the most cost effective tools for the project manager.

(b) The coverage is global, that is GNSS can be used irrespective of the size and geographic spread of the project. It also provides a means to scale up operations with no additional cost.

(c) The services are available all round the clock, continuously, that is, there is no break in the services being provided by the system.

(d) The satellite constellation is maintained by a sophisticated support network spread around the world, which ensures accurate inputs to the user. In most of the other systems, the user has to maintain the system.

(e) Present day receivers are small and compact enabling their easy placement over vehicles and premises. They operate passively which enable their integration with any equipment provided the required signals are available.

(f) The GNSS signal power and structure is so designed that they do not interfere with other devices.

4 Improvements in GNSS constellations

The latest improvements in the GNSS field have made the advantages mentioned in the previous section even more attractive for the project managers. GPS which is the oldest system has been upgraded over a period of time and its accuracy has been increased. Table1 below gives the detailed improvements on accuracy that have occurred over a period of time on the standard positioning service [11]. From the table it is evident that the user can fix his position within 8.5 m from 2006 onwards, without any external processing. This has opened up newer possibilities for applications [1].

Table 1. Effect of GPS Modernisation on the Errors [11]

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Utilisation of GNSS for Monitoring Processes

S. No.

Error Source With SA (m)

Without SA (m)

Code on L2 and/or L5 (m)

With A-IIa

(m)

1 Selective Availability (SA) 24.0 0.0 0.0 0.0

2 Ionosphere 7.0 7.0 0.01 0.01

3 Troposphere 2.0 0.2 0.2 0.2

4 Orbit and Clock 2.3 2.3 2.3 1.25

5 Receiver Noise 0.6 0.6 0.6 0.6

6 Multipath 1.5 1.5 1.5 1.5

7 User Equivalent Range Error (UERE) 25.0 7.5 2.8 2.0

8 Horizontal Dilution of Precision (HDOP) 1.5 1.5 1.5 1.5

9 Standalone horizontal accuracy, 95% confidence

75.0 22.5 8.5 6.0

10 Implementation Date May 2, 2000

2003-06 2005-10

GLONASS which became dysfunctional due to the breakup of USSR has been restored to its full functional state by Mar 2013 [5]. China had published the Interface Connection Document (ICD) [3] for Beidou on 27 Dec 2012, thereby announcing that Biedou system is fully functional. The Galileo system has moved to In Orbit Validation (IOV) stage and there is one satellite per orbit and the signals are available for analysis. GAGAN satellites have been launched and it is in the final approval stage at present. GAGAN signal are available for users. MSAS is fully functional with the launch of its MSAS 2 satellite on 18 Feb 2006 [7]. When all these systems are fully in place, there will be more than 150 satellites giving helping in navigation world over. Figure 1 gives the coverage of all navigation satellites when all constellations are fully functional [2]. From this it is evident that India will stand to gain the maximum as the coverage is nearly the highest.

Figure 1. Average number of satellite coverage of all planned constellations [2]

5 Factors to be considered

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It may be noted that the magnitude of the errors stated at table 1 in respect of the sources are not constant. The errors keep varying continuously since all or most of the satellites of the constellation keep moving with respect to the user. Also, there other factors those are beyond the satellite constellation that influences the overall performance of the system. Project managers need to have good understanding of the following critical and important factors:-

(a) Ionospheric effect on accuracy. (b) No of satellites visible. (c) Dilution of Precision (DOP). (d) Multipath and Tunneling. (e) Augmentation Systems. (f) Differential Systems. (g) Multi GNSS Systems. (h) IT Solution Provider’s knowledge. (i) Understanding of GNSS by the stake holders. Ionospheric influence on Accuracy. Contrary to general belief, accuracy of the GNSS and their

receivers are not constant world over. Each system is optimized for the country or region of its origin and cannot be used directly over other region. Over the Indian region the Ionospheric errors influence the accuracy greatly since it is in the region of maximum ionospheric disturbances as seen from figure 2 [9].

The Ionospheric error correction model presented by Klobuchar (1987) [6] is good for higher latitudes

but no so in the tropical region [8]. In the lower latitudes, the ionospheric activity increases from morning to mid-day and reduces during the later part. The zone of activity also depends on the direction of the sun. Hence one solution–compensation model cannot be made for a region or country. The night time activity is greatly influenced by solar maxima [9]. Study by Meriwether et al [9] in Brazil shows prolonged periods of total loss of signals in the night. The solar maxima affect both directly and indirectly the GPS satellites since they produce ionospheric storms and magnetic storms [11].

Number of Satellites Visible. The GNSS positioning techniques primarily use trilateration technique.

For this there is a requirement of having inputs from three satellites. However to cater for receiver clock bias and height reading, five satellites are required to be visible to the user. Reading the corollary, it will be evident that if less than five satellites are used then the resultant positional data will not be correct. Availability of more than five satellites is very less over a specific area. Project managers should have alternate means of finding position when less than five satellites are visible. For many applications or functionalities, availability of four satellites may be adequate. To obviate periods of non-availability, modern day receivers take inputs from more than one constellation; most popular is the GPS and GLONASS combination

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Figure 2. Scintillation map showing frequency of disturbances during solar maximum [9]

DOP - Geometry of the Satellites. The availability of the satellites alone will not assure accurate

positional calculations. These satellites should also be in certain geometric dispersion over the receiver. This aspect given in a measurable quantity called GDOP should be less than 3 for most of the monitoring applications. The dilution of precision over a region can be predicted and during these times, that specific constellation should not be used. The geometric dispersion will be higher if satellites from different GNSS constellation are used. The table 2 below gives the Optimal GDOP values [4]

Table 2. Optimal GDOP values for applications [4]

DOP Value

Rating Description

1 Ideal This is the highest possible confidence level to be used for applications demanding the highest possible precision at all times.

1-2 Excellent At this confidence level, positional measurements are considered accurate enough to meet all but the most sensitive applications.

2-5 Good Represents a level that marks the minimum appropriate for making business decisions. Positional measurements could be used to make reliable in-route navigation suggestions to the user.

5-10 Moderate Positional measurements could be used for calculations, but the fix quality could still be improved. A more open view of the sky is recommended.

10-20 Fair Represents a low confidence level. Positional measurements should be discarded or used only to indicate a very rough estimate of the current location.

>20 Poor At this level, measurements are inaccurate by as much as 300 meters with a 6 meter accurate device (50 DOP × 6 meters) and should be discarded.

Multipath and Tunneling. In many construction projects such as building of dams, the project area

is closed by natural high raises likes mountains or by artificial high rises like buildings. The position of the user is calculated from the distance he is from the satellite, which in turn is measured by the distance travelled by the signal. The high raises around the project site reflect the signals and the receiver uses the reflected signal to calculate the position. Since the distance travelled by the reflected wave is more than the direct distance, the position calculated becomes in correct. There are regions within the project site that are covered by foliage, tunnels etc. where the GNSS signals do not reach altogether. A project manager should have the site

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validated for these reflections and tunnels, and the positional data received from these locations should be assumed to have errors and alternate means have to be catered for. One example of alternate method in a dam construction site is to have a traffic control personal standing at the start or end of the road that runs in the reflection or tunnel zone, who feeds the details about the trucks that cross him.

Augmentation Systems. In India, though GAGAN is for the civil aviation and is managed by Airports

Authority of India, the signals are available for anyone to use within the Indian subcontinent. GAGAN has been planned to improve the GPS accuracy to 2 m from the base 6 m. In the study conducted by the authors, it has been observed to give positional accuracy of about 2.5 m over Indian Institute of Technology Kharagpur. Hence, the project managers while using GNSS based monitoring over Indian region should insist on using latest receivers that use GAGAN signals.

In developed countries, there is more than one system of augmentation. For example in Continental

America (CONAM) there are WAAS and Wide Area Differential GPS Systems (WADGPS) available. Each has its own advantages and shortcomings. These have to be understood and that system which gives maximum advantage in a particular area has to be used. In some regions more than one system of augmentation satellites signal may be available. For example over the Middle-East countries both GAGAN and EGNOS signals will be available. Over the eastern India both GAGAN and MSAS signals are available. In this situation, only that system which is designed to give better accuracy over that particular region should be used.

Differential Systems. In some of the projects, differential systems are used in addition to the augmentation systems. In this, there is a base reference station whose position has been determined with very high precision. The GNSS error over this position is continuously monitored and the errors or offsets are considered to be valid for all receivers that operate around this base station. The error is transmitted in real-time over a particular frequency and the receivers use the error correction data to give better accurate positioning. But in actuality, since the project areas are generally new areas or remote areas, there is no pre-surveyed accurate point nearby. In this condition a suitable vantage point has to be selected for establishing the base station. This vantage point should be visible to all receivers that operate over the area. The positional data of this point should be interpolated from the base triangulation stations maintained by Survey of India. Care should be taken to get deduce the location with highest precision possible.

Multi GNSS Systems. As seen earlier, apart from GPS, the GLONASS and Beidou are fully

functional from Mar 2013. These systems also should be used for monitoring purposes. There is an agreement between GPS and GLONASS, due to which GLONASS now transmits, in addition to its signals, Code Division Multiple Access (CDMA) signals like GPS satellites for better compatibility. GPS/GLONASS dual system receivers are freely available around the world. Project managers should insist on using multi systems in their solutions as this gives specific advantages as listed below:-

(a) The availability of satellites for calculating position increase greatly. (b) When the dilution of precision in one system is high, the other can be used without break in

service. (c) The dilution of precision between the satellites of different systems is very less, since satellites in

different orbits inherently have better geometry. (d) By using two different transmission bands, the ionospheric delay can be reduced.

India has an agreement with Russia for use of GLONASS signals. Through this agreement, Russian government has assured availability of GLONASS signals over India. Extending the agreement between GLONASS and GPS, over Indian region these two systems will be available without disruption. This can be exploited by the project managers.

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IT Solution Provider’s knowledge. In one of the GNSS based monitoring projects that was studied by the authors, it was observed that the system was giving more than 100 m inaccuracy though very good quality receivers have been used on board the vehicles. On investigation, it was found that high accuracy positional data was being transmitted and received at the control station. However, the software that updates the database truncates the received data while updating the database. This is so because the database designer did not cater for the acceptance of geo data which generally has 10 digits for longitude and 10 for latitude. Further investigation revealed that the solution development team did not have any idea about GNSS. Since the inaccuracies were higher, the users had practically stopped using the GNSS inputs in monitoring the project. This brings out the importance of scrutinizing the developers and coders who are involved in the solution development at the project planning stage.

Understanding of GNSS by all stake holders. The essence of project management is “the

alignment of the project with stakeholders’ needs or objectives” [11]. They have the powers to influence the direction in which the project moves. The stakeholders are the source of capital for the project. The importance of stake holders management is seen by the fact that Guide to PMBOK dedicates one full chapter to this aspect. Hence it is essential that the stake holders also be appraised about the nuances of GNSS. In one of the resource quality monitoring processes of steel mine, studied by the authors, it was observed that the geologist recording the resource sample’s location, was taking GPS readings even though the satellite availability was just three. He did not check the availability factor before setting out for collection of samples. This resulted in wrong evaluation and the ore blending machine was creating trouble the next day. Hence, it is also essential that all staff involved in the monitoring processes should be sensitized about the key factors especially the GDOP and satellite availability parameters.

Therefore, from the above analysis and discussion it is evident that the project managers should

understand the sources of errors and strive to reduce them in order to increase the accuracy of positioning, constrained by the computation time and update frequency. Amongst the factors mentioned above, the project managers have control over the type of GNSS to be used, the augmentation to be used and the identifying the time period over which it is not to be used. These should be incorporated in the monitoring processes properly to achieve the required goals of monitoring processes. The other parameters are also critical but are beyond the scope of the present considerations because these need different algorithms to control the involved inaccuracies; whereas, it is considered that these three parameters form the key components to increase the performance of the monitoring processes.

6 Conclusion

As noted in section 3 above, GNSS has many advantages that make it the most suited technique for monitoring of the projects. The improvements in GNSS in recent times have made these advantages more lucrative for the project managers. While using GNSS for monitoring purposes, the project managers should take note of nine key factors mentioned at section 5 that are associated with the GNSS and the GNSS technology. They should develop deep understanding of the issues and should also educate all stake holders regarding the same. The involved staff members should be especially made aware of GDOP and availability issues. The coverage factor brought out in multipath and tunneling section, should be considered at the project planning stage itself and alternate means should be planned to overcome these difficulties. A good understanding of these key factors will enable better utilisation of GNSS technology which in turn will lead to close monitoring of project and will enable its completion in time, i.e., achieve the desired targets.

References

(1) Ahmed El-Rabbany, 2006, Introduction to GPS, Second Edition, Artech House, pp 139 – 160.

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(2) Andrew G Dempster, Chris Rizos, 2009, Implications of A “System of Systems” Receiver. (3) BeiDou Navigation Satellite System, Signal In Space Interface Control Document (Test

Version), China Satellite Navigation Office, released on 27 Dec 2013. (4) GDOP, Wikipedia, website http://en.wikipedia.org/wiki/Dilution_of_precision, accessed on 13

Jul 2013 at 0025hrs. (5) GLONASS Constellation Status, Federal Space Agency, Information-Analytical Centre,

website, http://ftp.glonass-ianc.rsa.ru/ accessed on 14 Mar 2013. (6) Klobuchar, J.A., 1987, Ionospheric Time-Delay Algorithm for Single-Frequency GPS Users,

Aerospace and Electronic Systems, IEEE Transactions on, vol. AES-23, no. 3, pp. 325,331. (7) Latest News, Inside GNSS, Mar 2006 issue. (8) Meriwether, J. W., J. J. Makela, Y. Huang, D. J. Fisher, R. A. Buriti, A. F. Medeiros, and H.

Takahashi, 2011, Climatology of the nighttime equatorial thermospheric winds and temperatures over Brazil near solar minimum, Journal of Geophysical Resources, 116.

(9) Paul M. K., Jr, Cornell University, Todd Humpreys, The university of Texas at Austin, Joanna Hinks, Cornell University, 2009, GNSS and Ionospheric Scintillations: How to survive the next solar maxima, Inside GNSS, July/August 2009, pp 22-30.

(10) Press release by ISRO, Jul 02 2013, PSLV-C22 Successfully Launches IRNSS-1A, India's First Navigation Satellite, ISRO website, www.isro.org, accessed on 13 Jul 2013.

(11) Project Management International, 2013, A Guide to Project Management Body of Knowledge, fifth edition, Chapter 2, pp 30.

(12) Project Management International, 2013, A Guide to Project Management Body of Knowledge, fifth edition, Chapter 3, pp 50.

(13) Shaw, M., Sandhoo, K., and Turner, D., 2000, Modernisation of the Global Positioning System, GPS World, September 01, 2000, pp36-44.

Authors’ Profile V Shanmuga Velan, is a retd army officer who had executed many projects in GIS and GNSS during his service from Jun 2003 till Nov 2011. He was part of the Integrated Space Cell of MoD looking after the GNSS applications. He is now pursuing research in the broad area of ‘GNSS Based Monitoring’ at Indian Institute of Technology Kharagpur. He can be contacted at Department of Mining Engineering, IIT Kharagpur, Kharagpur, 721302, Mob: +91 9564168932, mail: velan_vs@yahoo.co.in. His web page at IIT Kharagpur is http://www.dak.iitkgp.ernet.in/phd/profile.php?roll=11MI91S01 . Dr D Chakravarthy, is Associate Professor in the Department of Mining Engineering in Indian Institute of Technology Kharagpur. He teaches GPS and GNSS subjects apart from other mining engineering related subjects. He has executed many GNSS research and consultancy projects for the mining industry. He can be contacted at Department of Mining Engineering, IIT Kharagpur, Kharagpur, 721302, Tele: +91 3222 283708, mail: dc@mining.iitkgp.ernet.in His web page at IIT Kharagpur is http://www.iitkgp.ac.in/fac-profiles/showprofile.php?empcode=bUmVT&depts_name=MI. Dr P P Chakrabarti, is Senior Professor in the Computer Science and Engineering Department Engineering in Indian Institute of Technology Kharagpur. He is a subject matter expert in Artificial Intelligence. He is the receiver of different academic awards of national and international repute. He served as various academic committee heads as well as different administrative heads within and outside the institute. He has been instrumental in executing numerous research and consultancy projects for national and international clients through SRIC. At present there are several projects being executed by the SRIC at IIT Kharagpur. He can be contacted at Department of Computer Science and

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Utilisation of GNSS for Monitoring Processes

Engineering, IIT Kharagpur, Kharagpur, 721302, Tele: +91 3222 283466, mail: ppchak@cse.iitkgp.ernet.in