Digital field data acquisition: towards increased quantification of uncertainty during geological mapping

Models of the Earth’s geological structure are derived from a combination of field mapping, direct sampling of the underlying geology and indirect observation using geophysical techniques. Field mapping has traditionally involved the synthesis and reduction of large amounts of observational data to produce a map at a given scale that represents a 2D simplification of the actual 3D geological structure. The process of gathering and abstracting field data to produce an informative, representative map relies heavily upon the skill of the geologist, but this "skill" is an unquantified mixture of observational prowess, cartographic ability, prior experience, guile, guesswork, and "gut-feeling". The end result of the mapping process rarely, if ever, includes any reference to the tacit knowledge of the mapper, the prior information that has guided the mapping process, or the varying amounts of uncertainty associated with geological interpretation. These issues are even more acute when surface map data are extended to produce geological cross-sections and 3D structural models.
We believe that new digital mapping techniques can help to reduce some of the inherent problems of traditional field mapping. Digital structural mapping methods involve the acquisition of field data on hand-held computers operating Geographical Information Systems (GIS) software. Use of GIS as the primary tool for storing raw field data makes it possible to visualize the data at any level of abstraction from regional to outcrop scale in a seamless way, and prevents the segregation of input data from map-scale interpretation.
Real-time or post-processed Differential Global Positioning System (GPS) data can provide very precise geospatial (x,y,z) control on observations. . These recent advances in hardware and software technology mean that powerful multi-attribute mapping and high-resolution spatial analysis can now be carried out rapidly in the field. Field data may be directly imported to 3-D visualization, analysis and 4-D modeling packages, which can provide further constraints on the viability of ongoing interpretations. Such digital workflows provide opportunities to view and analyze data collected ‘insitu’ and facilitate an iterative approach to be adopted in structural problem solving.
Digital Structural Mapping provides precisely georeferenced field observations and forms a more rigorous basis for field data collection and interpretation. The positional accuracy means that repeatability and hence accuracy of observations is improved. The resulting data can be used more efficiently to construct 3D models and 4-D restorations and the increased positional accuracy reduces 3D geometrical uncertainty. Digital field acquisition will be a major contribution to attempts to use field-based geological prior information to pre-condition geophysical investigations.