A New Geodetic Infrastructure for Trinidad and Tobago

Keith M Miller, University of the West Indies Tyrone Leong, Lands and Surveys Division Silburn Clarke, Spatial Innovision Limited

Abstract

The advent of satellite positioning technology has led to a change in the physical realisation of geodetic control. Traditional survey monumentation is being replaced or enhanced with active GPS control that can provide data to users in a number of ways. The Government of Trinidad and Tobago upgraded its national geodetic infrastructure by installing a network of five active GPS reference stations across the islands. The system is designed to deliver data to users through cellular telephone service and the world wide web. A follow-on phase in 2007 will construct a MSK radio beacon service sited in the centre of the country. These new services are designed to enhance the quality of survey data that is acquired in the region, and to provide broad access to the use of modern technology to land surveyors, mappers, utility companies, academia and the various members of the wider position-fixing community. Local datum issues arise when integrating information acquired under the new technology, and this presents a particular problem on these islands that are spanned by a tectonic fault structure. This paper explains the concepts employed in designing the new geodetic infrastructure for the country, and highlights difficulties that arise in the local environment. Summary

The Republic of Trinidad and Tobago is following regional Caribbean trends in revising land registration methods to provide good title and hence improve the local economy through land tenure. Maintenance of transactions is paramount to sustaining the future of such development, and records of ownership together with State interests are best served by a digital system. Development of a spatial data infrastructure for land management demands accurate representation of the real world within the digital model. Land, communications, utilities, and so on will then comprise layers of a national information system, with a national geodetic control network providing the foundation for a common coordinate system. Existing national control monuments established using traditional methods, have suffered from destruction and deformation. They remain in inaccessible areas and point locations no longer accurately reflect relative positions.

A new geodetic infrastructure has been developed that will be accessible by a wide variety of users and provide consistency in national coordinates. A network of five GPS satellite receiving stations operate continuously to provide differential services at three levels. Firstly, a radio beacon that has yet to be installed will provide signals compatible with operators of marine and land based real time navigation equipment. Secondly, an internet based service will make data available to the land surveying and mapping communities for post-processing data acquired in the field. Finally, a high speed service is distributed through the cellular telephone services nationally to give a high precision real time differential service. Delivery of this component requires high speed updates with low latency, and this is achieved through use of modern communications and

information technology. A network hub operating with four computer servers manages the services and provides access to users.

The resulting new infrastructure not only serves the demands of modern positioning needs in government and industry, but also provides a tool for research. Stations within the network have been coordinated in an international reference frame and the relative motions of the islands forming the Republic of Trinidad and Tobago will be monitored internationally while also recording internal deformation. The Vision

The Government of the Republic of Trinidad and Tobago is currently implementing the Agricultural Sector Reform Programme-Technical Assistance Programme (ASRP-TAP), with funding support from the Inter American Development Bank. The ASRP-TAP involves assistance to a range of policy and institutional reforms to strengthen the performance of the agricultural sector. Through these reforms it is expected that the sector will increase its contribution to national income, generate foreign exchange and employment, strengthen the regulatory agencies and organizations, and foster economic diversification.

One of the specific areas of reform in the overall ASRP-TAP is the Land Use Policy and Administration component, which seeks to create a more dynamic land market and improve the management of State-owned lands.

The de facto tenure and information status may be described (Robertson and Johnson, 2005) as: • Land Tenure – State land and private lands being split (52% vs 48% respectively)

and with holdings of 86,000 parcels vs 334,000 parcels ( Land Policy 1992)

• Tenure regularisation and improved land registration urgently needed to overcome present levels of tenure insecurity and informality. 47% of all households do not have adequate title documents and the incidence of squatting is estimated at approximately 30,000 squatters.

• Land Information – generally incomplete and inaccessible.

As part of the ASRP, significant reforms have been made in the legal framework for land administration in Trinidad & Tobago. The Registration of Titles to Land, Land Adjudication and Land Tribunal Acts of 2000 (the Land Title Legislative Package) are the most important element of this legislative reform programme. The package of legislation envisages a nation-wide systematic adjudication process whereby the legal interests in every parcel of land in the country will be determined and registered in a new, more efficient ‘real property’ registry.

Under the Land Adjudication Act (2000) it is envisaged that the legal interests in every single parcel of land in Trinidad & Tobago will be determined through a systematic nation-wide adjudication programme. Specific geographical areas will be designated “adjudication areas” in turn, and every person claiming a legal interest in any lands in that area will be entitled to establish their legal rights. This process will continue until each parcel of land in the country has been adjudicated. Parcels currently registered under

the Real Property Ordinance will be transferred to the new registry through the adjudication process with limited investigation once there are no adverse claims, while unregistered land, whether held under deeds registered in the Deeds Registry or otherwise, would be subject to more thorough investigation and boundary definition. Where the rights are unclear there is a provision for the creation and registration of provisional rights, which can later be upgraded to absolute rights.

The interests adjudicated through this process will be registered in a new land registry created by the Registration of Titles to Land Act (2000). This new registry will replace both the ‘Old Law’ Deeds Registry system and the Real Property Ordinance registry – the two existing land registry systems. It is anticipated that this new, more effective, registry system will significantly improve efficiency, transparency and security of tenure for all citizens. Ultimately, in the new registry system relevant interests in every parcel of land will be recorded in the registry. These recorded interests are guaranteed to be correct by the State, thereby significantly increasing investor confidence and creating a more vibrant land market. Under this new system every relevant interest in a parcel can be determined by consulting a single folio for that parcel in the Register.

The Land Tribunal Act (2000) creates a new court for land matters, in particular for any appeals arising in the adjudication process conducted under the Land Adjudication Act. The Act also authorizes the Tribunal to determine appeals under other land related legislation.

Alongside these reforms to the Legal Framework, the Government has also made significant investments in developing an information technology and institutional framework to support a more effective land market. Information technology investments have been made in the Registrar General’s Department, the Lands and Surveys Division and the Lands Administration Division of the Ministry of Agriculture, Land and Marine Resources. During the period 1999-2001 the Government undertook a major institutional review, as part of the Land Use Policy and Administration Project (LUPAP) of the ASRP.

In January 2003, Cabinet appointed a Committee to advice on the implementation of the Land Title Legislative package and the design of a land administration programme. This Cabinet-appointed Committee comprises representatives of the Government agencies potentially involved in the implementation of the legislation and a land administration programme, as well as representatives of professional associations and academia.

The Land Title Legislative package was enacted in the year 2000, but has not yet been proclaimed. The proclamation into law is awaiting the creation of the supporting regulations.

The Government of the Republic of Trinidad and Tobago is putting in place resources to prepare draft regulations for the Land Title Legislative package and to finalise the design and implementation of the Land Adjudication and Registration Project.

In order to economically cover the territory within a reasonable timeframe with acceptable parcel surveys, it is essential that an economically feasible unit regularization rate for Trinidad & Tobago (adjudication and registration) be established.

The deliberate investments in reforming the legislative framework, in building the digital cadastral map base and in the constructing an active real-time geodetic infrastructure will culminate in the significant efficiencies needed for realising this feasible unit rate.

In realisation of these objectives, in 2005 an international consortium comprising Fujitsu Transactions Solutions Limited (www.fujitsu.com), Spatial Innovision Limited (www.spatialvision.com) and Trimble Navigation Limited (www.trimble.com) was selected to deliver a modern Active Geodetic Infrastructure to the Government of the Republic of Trinidad and Tobago (GoRTT). The new infrastructure now enables one-person real-time surveys and GIS data collection anywhere in the country and support the GoRTT’s Vision 2020 adjudication and regularisation objectives. Based on one network of Continuously Operating Reference Stations (CORS) and a single centralised control centre, the new geodetic infrastructure delivers archive data for post-processing, Real-Time Kinematic (RTK) survey-grade services and differential GPS information for mapping and navigation.

The technology based geodetic system is managed by the Lands and Surveys Division (LSD), within the Ministry of Land, Agriculture and Marine Resources with support from specialist staff from the Department of Surveying and Land Information at the University of the West Indies. With both the CORS and the single base RTK components of the system now fully operational, and the Network RTK element under test, the surveying community are making use of data being delivered. The objective now is to ensure sustainability through maintenance and support. Trinidad and Tobago

The twin island state lies at the extremity of the Caribbean to the South East of the region as shown in Figure 1. Natural reserves of oil and gas have been exploited since 1902, and continue to provide a primary resource that attracts industry and development, which is focussed in Trinidad. Tobago has a larger tourist industry, and provides an idyllic escape for Trinidadians on a short vacation. Infrastructural development of roads, bridges, other communications networks and utility services is continuously ongoing on both islands. Agriculture exists on both islands, operating under small holdings. Provision exists for farmers to lease state lands for agriculture, and lands of the former state owned sugar plantations are now being distributed for such purpose. Continued development in industrial and agricultural sectors provides a need for positioning technologies in a wide range of diverse, but associated applications. In addition to the land adjudication process, for which the geodetic infrastructure was developed, it will also be used in government and commercial projects for planning, development, mapping, GIS, and for research.

Trinidad and Tobago lie within the active tectonic zone that separates the Caribbean tectonic plate from that of South America. The geology of Trinidad is particularly complex, with evidence of ongoing deformation in both horizontal and vertical components. Figures provided by Saleh et al (2004) suggest that relative horizontal motion of the existing national geodetic control is about 0.5 m since observations took place in the early 1960’s. An estimate provided by Miller (2005) indicates vertical displacement of 0.1 m over this same period. Both comparisons are made between North and South Trinidad, and more localised deformation will have a greater effect in some areas. Due to the lack of a suitable infrastructure, geodetic studies to determine national

deformation require extensive observation campaigns, and the new infrastructure will lead to a better understanding of local tectonic activity that is likely to impact on future planning and development policy.

BDOS

TEGU

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SCUB

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KOUR

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St.Croix

Figure 1. Location of Trinidad and Tobago, and CORS Sites within the Caribbean.

Requirements

Surveyors and other professionals within the geosciences in both commercial and government sectors are making use of satellite positioning technology within Trinidad and Tobago. The lack of a suitable infrastructure has hindered operations. Some, such as the Water and Sewerage Authority (WASA) have installed their own GPS base station, and the coordinates of each individual installation are not tied together. Other operators tie GPS surveys to existing control that has suffered from human disturbance as well as localised and national deformation. A primary purpose of the new geodetic infrastructure is to provide control at a national level that will ensure compatibility of coordinates between all users. Within this framework, and through the design of the new system, users with different interests will be able to use the network in different ways.

• Establish temporary physical marks through short term static GPS observations that are post-processed. These marks will then enable surveyors to utilise traditional survey instruments within the new infrastructure, and all survey work can be tied to the new control.

• Operate one dual frequency receiver connected to a digital cellular telephone to provide real-time positioning within the national network to an accuracy of 1cm horizontally. This is achieved through differential corrections based on Virtual Reference Station (VRS) technologies being applied within the mobile unit from the processing of data from multiple base stations simultaneously.

• Establish further geodetic networks consisting of physical marks on the ground that can be re-observed at regular intervals to determine localised deformation within the national scheme. The CORS sites themselves will be monitored within an international framework.

Demands of the extensive industrial offshore positioning market is currently being met by commercial GPS correction service providers. There is however, a need for services to associated marine services such as supply vessels and other commercial shipping entering Trinidad and Tobago waters. A radio beacon that will broadcast signals beyond reach of cellular telephone signals, and provide service of reduced accuracy at no cost is currently under construction. Design

A minimal number of five GPS stations was selected to provide coverage, such that the land mass of both islands is effectively surrounded by the network. Locations are shown in Figure 2. Hardware installed at each site includes a Trimble NetRS receiver with Zephyr geodetic antenna. At four of the sites the antenna is on a rooftop location with a three inch steel pipe fixed firmly to raise the antenna above other installations and obstructions. In all of these cases flat roofs provide easy access for maintenance, and the buildings were selected for accessibility, security and proximity to national telecommunications. Such a site could not be located in South West Trinidad, and a structure was erected to host the antenna consisting of a 6 m pole fixed in a substantial concrete base. At this height the antenna is raised above the level of a single storey building nearby where the receiver and communications are installed. A 2.2 KVA uninterruptible power supply installed at each site ensures continuous power to the receiver and to each Cisco 1841 router that provides communications with the Network Operations Centre (NOC).

The NOC is located at the Lands and Surveys Division on Fredrick Street, Port of Spain, Trinidad. From this location the five GPS sites can be monitored, and remotely managed. Data acquired is received, stored, managed and distributed from the NOC. The following equipment is installed at the NOC, and configured as shown in Figure 3.

• Dell Poweredge 2850 Servers - VRS Server, Archive Server, Web Server • Dell PowerVault 220S Storage Array • Dell PowerVault 132T LT02 Tape Unit • 3Com SuperStack 3 Switch 490012 port • Cisco 2821 Router • USRobotics 56K Dialup Modems • Tripplite SU 6KV A and 10KVA UPS

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Figure 2. Locations of Permanent GPS Installations in Trinidad and Tobago

Figure 3. Configuration of Installations at the NOC.

The three main components of this NOC are the RTKNet Server, the Web/Archive Server and the GPStream Server. These make up the computing cluster of the NOC.

• The RTKNet Server is the central computational processor for the network. The RTKNet processor models the various network corrections and maintains a continuous quality monitoring on the results.

• The Web server operates with Trimble GPServer and GPSWeb software, along with other web delivery applications, to distribute archived data through the world wide web.

• The Archive Server, co-located with the Web Server, stores data acquired at the CORS sites, and is equipped with 3 Terabytes of storage capacity and a high density DAT tape drive.

• The GPStream Server manages the data streams from the CORS source to the real-time end user services. RTCM corrections are delivered to users connected through dial up services from cellular telephones, or by internet protocol from a PDA.

Data transfer through the servers at the NOC is shown in Figure 4. Server #1

Server #2: RTKNetServer

RTKNet Processor

RTCM GeneratorsGPStream (Splitter) GPS Data

fromReference Stations RTCM Corrections

(to GPRS users)

RINEX Files (to web server)

GPStream (Line Relay)

Server #3: GPServer

Data Logging

Web Services

RINEX Files

Figure 4. Data Flow Through the NOC.

Communications between the NOC and CORS sites takes place through a wide area network (WAN) service that employs frame relay. The Telecommunication Services of Trinidad and Tobago (TSTT) frame relay WAN links are combined into one link at the main site (NOC). This means there will only be one link entering the NOC. This is one of the advantages of using frame relay over leased line; the links use packet switching technology so multiple logical links can run over the same physical link. The physical advantage of this is that there is no need to support five serial lines (1 from each Remote CORS site) at the NOC. This provides flexibility and plans for the future. Currently a 256K pipe goes into the NOC. If, in the future, there are requirements for more remote sites to be added and/or more bandwidth, then modules can be used to support up to 1.5 mbps, if desired, at the NOC. The current frame relay system avoids significant latency in

the transmission of data from the CORS sites to the NOC. The lag is less than 1 second and this allows for real-time capability within the VRS system.

The system is highly resilient with several layers of redundancy built-in including: a. back-up power systems at each remote station and at the NOC b. fail-over systems for the TSTT frame relay link using dial-up modems c. RAID-based storage systems backed by high density tape drives d. Multi-server cluster for enabling flexible reconfiguration

International Control

Coordination of the GPS CORS sites in Trinidad and Tobago is complicated by the scarcity of international sites regionally through the Caribbean, as shown in Figure 1.

Figure 5. Result of International Network Adjustment.

Baselines between the Trinidad and Tobago CORS and the external sites are long, which introduces differences in ionospheric and atmospheric conditions between signal paths from the satellites. Eleven days of data were used from international sites in St Croix (CRO1), Barbados (BDOS), French Guiana (KOUR), Colombia (BOGT), Nicaragua (MANA), and Cuba (SCUB), with each day being processed separately. Precise satellite ephemeredes from the International GNSS Service (IGS), and ionospheric models from The Astronomisches Institut at the University of Bern were used in processing data. Over the long baselines to the external control a solution that resolves carrier phase ambiguities on the baselines to integer values cannot be achieved. Much higher precision is available on the local baselines within Trinidad and Tobago. This is reflected in the weighting applied within the network adjustment, and in adjusting observations between all stations simultaneously the integrity achieved locally is retained. Results from one day of processing are shown in Figure 5 where horizontal error ellipse and vertical precision are shown at 68% confidence levels.

While the Trimble Total Control (TTC) software used for processing GPS data reports on the level of precision that is achieved on each day of processing, a better measure of accuracy is gained by comparing results between days. Standard deviations from the eleven days are slightly different between stations, but all better than 4 mm in the North component, 6 mm in the East, and 8 mm vertically. Final coordinates are given in an International Terrestrial Reference Frame (Altamimi et al, 2002), ITRF2005 at an epoch of February 21st 2007. These are provided with CORS data on download and used as the points of reference in computing corrections delivered through the VRS service.

To test the internal integrity of the resulting coordinates, which is of most value locally, a static GPS receiver was set up at the University of the West Indies (UWI) for two days in April 2007. The 48 hours of data was initially processed as two 24 hour data sets. In obtaining coordinates, adjustments are made to each of the computed baseline vectors from the CORS sites to UWI. Computed corrections are provided in Table 1 where the largest value is 10.4 mm in the height component from the farthest CORS station in Tobago.

Residual (mm) Day 1 Day 2 Baseline from

CORS at East North Height East North Height

Albion -6.4 1.4 8.3 -2.0 -1.4 8.0 Grande 0.3 -0.7 4.3 -0.3 1.7 -5.3 Galeota -0.8 0.3 4.5 -0.9 -0.9 2.0 Fortin 1.3 0.0 -6.7 -1.8 1.9 1.5 Calder 8.4 2.1 -10.4 8.2 1.5 -6.5

Table 1. Baseline Residuals for Each Day.

Resulting latitude, longitude and height values for the two days are given below, where the difference in East and North components are both less than 1mm, and difference in height is 6mm.

Day 1: 10° 38’ 24.44972” N 61° 24’ 02.17669” W -21.807 m Day 2: 10° 38’ 24.44974” N 61° 24’ 02.17670” W -21.813 m

Results of final adjustment within TTC using the two days of data combined is shown in Figure 6, which suggests that at UWI an accuracy of 0.9 mm has been achieved horizontally and 3.7 mm vertically. The resulting horizontal ellipse is scaled to one standard deviation and is circular in shape. The amount of data used here is excessive in comparison with that which would normally be used in application, but results demonstrate the consistence achievable internally within the network. Access to CORS data

For post-processing of data acquired at one or more static GPS receivers, data from the Trinidad and Tobago CORS network is available through world wide web access. A RINEX shop has been established at the registered web site www.gpstt.com where data is ordered from particular sites for requested periods and epochs. Data is archived at one second epochs. A typical order is shown in Figure 7, where data from all five sites has been requested for a full 24 hour day at 30 second epochs. Coordinates of the sites are embedded in the RINEX (Gurtner, 1994) data that is delivered either by download, or by

email. Use of RINEX format files means that data is compatible with any GPS processing software.

Menu options shown on the left of the display in Figure 7 provide access to other pages giving integrity and monitoring information for the network.

Figure 6. Results of Baseline Processing from CORS to UWI.

Figure 7. Obtaining CORS Data from www.gpstt.com

Access to the VRS

To utilise real-time positioning services users require a dual frequency GPS receiver with VRS capability connected to a cellular telephone with GPRS, or to a PDA. Access to the VRS server at the NOC is provided through internet protocol (IP) address, which must be known to the user. Data is streamed from the NOC to the field survey GPS equipment in RTCM format, which is independent of manufacturer. The primary limiting factor of this service is cellular telephone coverage. Access is available through both of the local service providers, TSTT and Digicel, and when coverage of the islands is combined the populated and industrial regions are within reach of a signal. However, some of the more remote and isolated locations are not covered. While connected to the service the user is required to pay for the cost of the ongoing call, and this will continue for the duration of the survey.

Use of the VRS in Trinidad is dependant on data from the four stations on the island. These are already situated at the extreme limits in comparison with the recommended 30-50 km spacing, and the Tobago site will also be a requirement for operating in North East Trinidad. There is no redundancy within the network, and reliability is of primary importance when potential users are considering the investment in receiving equipment. Within Tobago it is anticipated that the station at Calder will be used as a single station service for Real Time Kinematic (RTK) work using services of this station alone from the VRS server. This will operate within a range of about 20km and cover all but the northern most part of the island. Discussion

Installation of the Government of Trinidad and Tobago GPS network is based on modern equipment, software and communications technology. The CORS component is already in use by commercial surveyors who have invested in GPS receivers from different manufacturers including Trimble, Ashtech, Javad and Topcon. The Lands and Surveys Division of GoRTT are also applying CORS data in the management of state lands. Use has been limited to control survey work and point positioning where static data is acquired. Typical applications are the establishment of control for use with traditional surveys for construction and land division, for aerial photography, and for satellite imagery. Use of the network in this capacity requires that the surveyor invest in a dual frequency GPS receiver as an additional piece of survey equipment that compliments traditional instruments. Those that have already invested have purchased receivers in pairs, most with radio link and full RTK capability.

The VRS network that would eliminate the need for a surveyor to establish an RTK base station independently has yet to be commissioned. Initial tests have demonstrated its operation for short periods, but it has yet to be accepted and applied to a full survey. The five site installation provides a minimum requirement, and difficulties have been experienced with the TSTT frame rely service, on which this component is dependant. One or more stations have often been inaccessible in real-time, and this has delayed final testing of the system. However, in recent months reliability has improved, and TSTT have been quicker to respond to outages. It is anticipated that the VRS component will be accepted by GoRTT within two to three months. Equipment purchased by surveyors in

recent times has the capability of operating within the VRS service, and the purchase of receivers in pairs will give them the capability to operate two units as rovers simultaneously.

The CORS sites were coordinated in an international framework in February 2007, and they will have already moved within this frame of reference. The difference in velocity between North and South Trinidad is thought to be about 10mm a year with a primarily Easterly component, and the velocity of Tobago relative to Trinidad is unknown. Within a year the relative locations will have moved beyond the tolerances used in determining their coordinates. It is hoped that at least one of the stations will be adopted by an international agency and incorporated into regular adjustments at this level. Velocities of other stations within the network can then be relatively determined. References

Altamimi Z, Sillard P. and Boucher C., 2002. ITRF2000: A New Release of the International Terrestrial Reference Frame for Earth Science Applications. Journal of Geophysical Research, American Geophysical Union, Vol. 107, No. B10, 2214, pp 2.1-2.19.

Gurtner W., 1994. RINEX: The Receiver Independent Exchange Format. GPS World, Vol. 5, No. 7.

Miller KM., 2005. Variations in Sea Level on the West Trinidad Coast. Marine Geodesy, Taylor and Francis, Vol. 28, pp 219-229.

Robertson H. and Johnson S., 2005. Implementing the Trinidad and Tobago Land Adjudication and Registration Project, Real Property Rights Forum, Ministry of Land and Marine Resources, Trinidad.

Saleh J., Edwards K., Barbaste J., Balkaransingh S., Grant D., Weber J.C. and Leong T., 2004. On Some Improvements to the Geodetic Infrastructure of Trinidad and Tobago. Survey Review, The Commonwealth Association of Surveying and Land Economy, Vol. 37, No. 294, pp 604-625.