EVALUATING THE APPLICATION OF CLOSE RANGE PHOTOGRAMMETRY FOR GEOLOGICAL MAPPING

Photogrammetry, the science of extracting measurement information from a sequence of overlapping aerial photographs, has been used for producing regional scale topographic maps for many years. Close range photogrammetry, which has been used extensively for forensics and engineering, employs the same fundamental principles as those used in aerial photography. Given a series of photographs taken from known locations and fixed camera orientation it is possible to render 3D images of observed objects.

To apply this methodology to geological mapping required the development of field procedures to address specific tasks. Camera orientation is controlled by the use of multiple bubble levels. The relative position of the camera is defined by geodetic surveying, with the absolute location of the camera and reference points on the viewed surface established by the use of a sub-centimeter resolution GPS unit.

Results using this methodology will be presented for two geological sites. First, the Chelmsford Formation is a coarse-grained sandstone unit, found within the Sudbury Structure. The depositional age of the Chelmsford is bounded below by the Sudbury Igneous Complex (1850 Ma) and above by the intrusion of the Sudbury Olivine diabase dikes (1248 Ma). Locally, bedding plane surfaces of the sandstone display textures that have been described as either trace fossils or sediment dewatering structures. The mapping of a large bedding plane surface using the proposed technique will make it possible to use the morphology, dimensions and distribution of these features to distinguish between the two interpretations. Second, Sudbury Breccia is a generic term that has been used to describe the relation between breccia bodies and the Sudbury Impact event. Appearing in many different lithological guises, one variant is comprised of rotated sedimentary clasts within a laminated argillite sequence. At this location the photogrammetry technique will be used to derive a numerical estimate of the clast morphology. Detailed analysis of the shape of the clasts will help define the formation process for this variant of Sudbury Breccia. These field examples will illustrate how high resolution photogrammetry derived micro-topographic variations can be used to provide quantitative constraints on the nature of geological processes.