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Abstract
Demand for high-accuracy spatial data has never been higher. Whether for traditional uses, such as precise location of property boundaries, or more innovative applications, such as augmented reality apps showing the location of buried infrastructure, high accuracy is expected and essential. On a dynamic planet, where plate tectonics and other phenomena cause constant movement of all objects on the Earth’s surface, this is also a considerable challenge, particularly at local scales where deformation can vary rapidly over short distances. The cost of geodetic survey data collection at high resolutions can be prohibitive. But if this local deformation is not accounted for in a national datum, that datum cannot be said to fully meet the positioning and data management needs of the local community. Consequently, this inhibits analysis and decision-making on regional and national scales, since there may be numerous areas of local deformation in a country.
This research investigates two low-cost alternative data sources, not previously used for direct modelling of ground movement within a national datum: digital cadastral data for horizontal modelling and synthetic aperture radar data for vertical modelling. The success of these alternatives is demonstrated through their application to three deformation scenarios where high-resolution models are essential: earthquake-induced shallow ground movement, deep-seated earthquake movement in urban areas and ongoing subsidence due to geothermal activity.
A prototype model is incorporated into the geodetic datum and used to answer important questions relating to the impact of deformation on infrastructure and property boundaries. In addition, an automated approach to regularly updating a high-resolution model is developed, using cadastral data collected over a period of several years after an earthquake. This study also introduces a novel approach to updating height control within the national datum in the aftermath of an earthquake, recognising that it may be some time before full resurveys can occur. Overall, this research clearly demonstrates that high-resolution modelling significantly enhances the usefulness of the national geodetic datum, without requiring expensive additional data collection.