Papers by Richard Wonnacott
TrigNet The Network of Active GPS Base Stations for South Africa
The FIG Task Force on Institutional and Organisational Development has taken forward a programme ... more The FIG Task Force on Institutional and Organisational Development has taken forward a programme of work to assess the particular challenges to building organisational capacity. The Task Force developed, tested and refined a self-assessment questionnaire to determine capacity at system, organisation and individual levels; this was made available to and completed by professionals from many countries. In reviewing the responses to the questionnaire, FIG also considered other recent work including that of the UN FAO (2007), AusAID (2008) and Land Equity International (2008). This work (which is described in more detail in Greenway (2009)) led FIG to draw the following broad conclusions: • Cooperation between organisations is a weak point: there is often suspicion rather than cooperation; • The remits and skills of the different organisations involved in administering a land administration system are often not joined up effectively; • The lack of effective working across sectors is a pa...
AFREF: Concept, Progress and Permanent GNSS Networks in Africa
Current Situation of AFREF and First Results from GNSS Networks in Africa
African Geodetic Reference Frame and First Results from GNSS Networks in Africa
The South African network of dual-frequency global positioning system satellite receiver base stations: a national asset with many applications and research opportunities
ABSTRACT THE SOUTH AFRICAN NETWORK OF DUAL-frequency global positioning system (GPS) receivers pr... more ABSTRACT THE SOUTH AFRICAN NETWORK OF DUAL-frequency global positioning system (GPS) receivers provides an opportunity to add significant value to the information obtainable from satellite-borne GPS transmitters. Whereas mobile single-frequency GPS receivers are used mostly for navigation and asset tracking, the dual-frequency GPS receivers, located at fixed base stations in South Africa, permit applications that include land surveying, geodesy, monitoring of movements of the Earth's crust, time transfer, local real-time ionospheric mapping, and weather prediction based on the derivation of the total precipitable water content in the atmosphere. For most of these applications, the information derived from the local network of GPS base stations is highly specific to South Africa and provides a significant improvement in the accuracy, spatial distribution and frequency with which the derived data can be obtained, compared to conventional means. This paper presents the principle of operation andbenefitsofdual-frequency GPS receivers, the current status of the deployment of these receivers in southern Africa and some details about the scientific applications and research opportunities which may be derived from the data of the South African dual-frequency GPS receiver network in particular.
Richard Wonnacott highlights the importance of a uniform coordinate reference frame for sustainab... more Richard Wonnacott highlights the importance of a uniform coordinate reference frame for sustainable regional development
海外ジオマチックス情報 AFREF:測地基準系整備に向けて アフリカのためのアフリカ主導のはじまり
Survey Review, 1999
ABSTRACT
Although primarily designed for positioning applications, Global Navigation Satellite Systems (GN... more Although primarily designed for positioning applications, Global Navigation Satellite Systems (GNSS), which currently included the Global Positioning System (GPS) and the Global'naya Navigatsionaya Sputnikoyaya Sistem (GLONASS), have developed into a multidisciplinary tools for navigation geodesy, surveying, atmospheric science, disaster management and so on. Any regional or cross border development programmes in Africa which are based on geospatial information can only succeed if they are based on a modern uniform co-ordinate reference frame which is consistent with an international global reference frame. The Africa Reference Frame (AFREF) project is a geodetic project designed to unify the co-ordinate referenc frames of Africa and is based on network of permanent GNSS stations. The presentation will briefly describe the AFREF project and its progress to date as well its importance for the provision of uniform geospatial information. Examples from Africa will also be presente...
SUMMARY A uniform coordinate reference system is fundamental to any project, application, service... more SUMMARY A uniform coordinate reference system is fundamental to any project, application, service or product that requires some form of geo-referencing. Most countries in the world have established such reference systems that are used for national surveying, mapping, photogrammetry, remote sensing, Geographical Information Systems (GIS), development programs, and hazard mitigation (earthquake studies, fault motion, volcano monitoring, severe storms, etc). Many of these national coordinate systems are based on reference figures of the Earth which are somewhat outdated and, when based on a local origin or datum point, are restricted to a particular country, making cross-border or regional mapping, development, and planning projects very difficult indeed. In some instances, more than one datum has been used within a country. When using modern positioning technology such as GPS, technical understanding and careful mathematical manipulation is required to relate GPS derived coordinates t...
This paper examines quality and integrity issues that need to be managed in order to successfully... more This paper examines quality and integrity issues that need to be managed in order to successfully operate a real-time CORS network. Important concepts in quality control such as data availability, latency, multipath, atmospheric effects, and interference are discussed. These quality indicators are examined in the context of their capacity to indicate potential problems that can degrade the quality of real-time network positioning. The issue of intelligent alerting is raised and an alternative strategy, based on the use of relative thresholds, is proposed with the aim of reducing the number of unnecessary alerts provided to operators. South Africa’s CORS network TrigNet is used as a case study to test some of these concepts. 1.
South African Journal of Geomatics, 2015
South Africa is a water scarce country hence the careful monitoring and management of available w... more South Africa is a water scarce country hence the careful monitoring and management of available water resources is critical for the wellbeing of the citizens of the country. A high percentage of the Earth's water supply is stored underground which can be extracted either through pumping or using artesian pressure. This paper describes the application of GNSS, InSAR and In-Situ Micro Gravity measurements for the monitoring of an artesian wellfield in the Oudtshoorn District in the Western Cape province of South Africa. GNSS receivers were run continuously for a period of 133 days between March and August 2014 to detect possible surface subsidence during pumping and artesian free flow extraction of water in the wellfield. Two InSAR scenes were processed, one during the peak period of water extraction from the wellfield and the other approximately 4 months after all boreholes were closed and pumps switched off. A micro-gravity campaign was conducted over two days in the wellfield with the gravity meter co-located at one borehole which was opened on the second day of the campaign. The results from the GNSS monitoring showed a subsidence of approximately 15 to 20 mm at the peak of the free flow and pump while those from the InSAR and microgravity measurements were largely inconclusive.
海外ジオマチックス情報 AFREF:測地基準系整備に向けて アフリカのためのアフリカ主導のはじまり
測量, Feb 1, 2006
The propagation of the Global Positioning System (GPS) signal from the satellite to the receiver ... more The propagation of the Global Positioning System (GPS) signal from the satellite to the receiver is affected by, among other factors, the atmosphere through which it passes and, whereas the effects of the ionosphere can be eliminated by the differencing of the two transmitted frequencies, the effects of the troposphere remain one of the major sources of noise in traditional geodetic and positioning applications of GPS. This noise can, however, be turned into a signal for the meteorologist and, by applying suitable constraints and processing strategies, it is possible to estimate the amount of precipitable water vapour (PWV) in the atmosphere. The application of the GPS data for the estimation of PWV in the atmosphere is not a new concept and has been described in many publications and reports since the early 1990's. This project is, however, an attempt to test the technique using the South African network of permanent GPS base stations. This paper describes the fundamental principles and the testing of the estimation of PWV using GPS and meteorological data from a network of nine permanent GPS base stations in South Africa. The results of the GPS derived estimates have been verified against upper air measurements from radiosonde ascents from a sub-net of five of the nine stations as well as with PWV estimated from a numerical weather model (NWM).
The FIG Task Force on Institutional and Organisational Development has taken forward a programme ... more The FIG Task Force on Institutional and Organisational Development has taken forward a programme of work to assess the particular challenges to building organisational capacity. The Task Force developed, tested and refined a self-assessment questionnaire to determine capacity at system, organisation and individual levels; this was made available to and completed by professionals from many countries. In reviewing the responses to the questionnaire, FIG also considered other recent work including that of the UN FAO (2007), AusAID (2008) and Land Equity International (2008). This work (which is described in more detail in Greenway (2009)) led FIG to draw the following broad conclusions: • Cooperation between organisations is a weak point: there is often suspicion rather than cooperation; • The remits and skills of the different organisations involved in administering a land administration system are often not joined up effectively; • The lack of effective working across sectors is a particular issue; • There are skill gaps, particularly in the conversion of policy into programmes, the division of labour, and ensuring effective learning and development; • Stakeholder requirements appear insufficiently understood or insufficiently balanced, leading to ineffective use of outputs; • There is insufficient time and effort given to learning from past experience. The Task Force considered the results of its analysis and came to the view that a number of key components need particularly to be considered by those who want to build sustainable institutional and organisational capacity in the field of land administration. The Task Force therefore created an FIG Publication providing guidance to managers on organisational capacity building, focussing on these key components. This paper summarises the work and output of the FIG Task Force on Institutional and Organisational Development.
Nubia rigid plate motion as seen from far south
The motion and the rigidity of the Nubian plate provides a critical constraint to the geodynamics... more The motion and the rigidity of the Nubian plate provides a critical constraint to the geodynamics of the surrounding plates. Unfortunately, the sparse distribution of geodetic continuous GNSS stations across the plate does not provide a high precision solution for an Eulerian pole and to test statistically for the rigidity. The presence of 3 separate cratons, Rift Valleys, and old
How rigid is a rigid plate? Geodetic constraint from the Kalahari craton, South Africa
The motion and the rigidity of the Nubia plate provide critical constraint to the geodynamic of t... more The motion and the rigidity of the Nubia plate provide critical constraint to the geodynamic of the surrounding plates. Unfortunately, the sparse distribution of geodetic continuous station across the plate does not allow to solve with high precision Eulerian pole and to test statistically for the rigidity. The presence of 3 separates cratons, rift valleys, and old deformation belts along
Uncertainty estimation of the velocity model for the TrigNet GPS network
Satellite based geodetic techniques - above all GPS - provide an outstanding tool to measure crus... more Satellite based geodetic techniques - above all GPS - provide an outstanding tool to measure crustal motions. They are widely used to derive geodetic velocity models that are applied in geodynamics to determine rotations of tectonic blocks, to localize active geological features, and to estimate rheological properties of the crust and the underlying asthenosphere. However, it is not a trivial
A New Vertical Datum for South Africa?
ABSTRACT
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Papers by Richard Wonnacott