STEPPING FROM THE PAST TO THE FUTURE: CLOSE-RANGE PHOTOGRAMMETRY AT THE LAETOLI FOOTPRINT SITE IN TANZANIA

The Laetoli footprint site in Tanzania records footprints made by several individuals while traveling across a layer of volcanic ash 3.6 million years ago. These fossil footprints may be the earliest evidence of bipedal locomotion and upright stance of our human ancestors. In February of 2011 at the direction of the President of Tanzania, a 3.5 meter long section of the Footprint Tuff was re-excavated to evaluate and document the condition of the footprints. Stereoscopic imaging was conducted using a remotely triggered digital SLR camera mounted on a monopod to obtain overhead images of the re-excavation stages culminating with the footprint tuff. Imagery acquisition averaged approximately 25 minutes per layer and was of minimal impact to the excavation process. Multi-stage imagery was placed in a common coordinate space and used to generate 3D point clouds, surfaces, and associated "aerial" orthophotographs. These data sets allow for a virtual re-excavation, as over 13 layers of materials can be digitally removed to expose the final footprint surface. Close-range photogrammetry was chosen for this documentation based on it’s proven effectiveness in capturing high quality 3D data in remote areas of the western United Sates. Advances in digital cameras, computer architecture, and multi-view matching software, make it possible to take photos and produce a final data set in a matter of minutes. In addition the technique is much more portable, allowing the capture of stereoscopic photos to be conducted by field personnel. This makes close-range photogrammetry an effective method for capturing important data about a wide variety of features. Stereoscopic photography has been utilized to obtain 3D data for fossil footprint sites and rock art locations on public lands managed by BLM. Not only does photogrammetry provide an effective method to evaluate changes in natural subjects, but it also provides insight into the errors which can be propagated through multi-generational cast replication, such as exhibited in those of the famous Laetoli footprints.