APPLICATIONS OF LOW ALTITUDE PHOTOGRAMMETRY FOR MORPHOMETRY, DISPLACEMENTS AND SURFACE CHANGE

Acquisition of low-altitude aerial imagery using small aerial vehicles (tethered and untethered) is an emerging capability that can greatly enhance field-based geological investigations. Photogrammetric applications of small aerial systems have also benefited from the proliferation of image processing techniques (e.g., structure-from-motion) and robust, but compact, optical systems. High-resolution, close-range photogrammetry produces dense, 3-dimensional point clouds that facilitate the construction of digital surface models, as well as a potential means of classifying ground targets using spatial structure. Herein, we present results from recent applications of low-altitude aerial photogrammetry, including high resolution surface morphometry of a lava flow, as well as repeat-pass applications to landslides and soil erosion. Aerial photos are typically acquired at altitudes of 80 – 100 meters above the ground surface. In all cases, high-precision ground control points are key for accurate (and repeatable) orientation – relying on low-precision GPS coordinates (whether on the ground or geotags in the aerial photos) typically results in substantial rotations (tilt) of the reference frame. Using common ground control points between repeat surveys results in matching point clouds with RMS residuals better than 10 cm. In arid regions, the point cloud is used to assess lava flow surface roughness using multi-scale measurements of point cloud dimensionality. For the landslide study, the point cloud provides a basis for assessing possible displacements. In addition, the high resolution orthophotos facilitate mapping of fractures and their growth. For smaller areas, tethered systems may offer advantages over untethered systems, including the potential for greater lifting capacity and longer ‘flight’ times. In summary, there is a wide ranging toolbox of low-altitude aerial platforms becoming available for field geoscientists. In many instances, these tools will present convenience and reduced cost compared with the effort and expense to contract acquisitions of aerial imagery.