Using photographic measurement and gigapixel panoramas to study changes in a Lake Michigan sand dune

Abstract

Detailed measurements of changes in aeolian landscapes help researchers better understand aeolian processes and monitor the effects of climate change in these systems. This study focuses on a photographic method to measure sand surface changes. It introduces custom erosion pins (photoscale pins) designed to allow proper scaling of measurements taken from digital images or high resolution (gigapixel) panoramas. Furthermore, this study discusses errors associated with measuring photoscale pins photographically. Resolution errors arise when marking object boundaries on digital images. These typically affect measurement precision, but even so, differences between repeated measurements of the same pin average 0.58 mm. Perspective errors arise when pins are tilted relative to the camera’s line of sight and introduce bias, affecting measurement accuracy. Photographic measurement can allow remote surveillance, reduce site disturbance, increase the frequency of observation, and reduce measurement error compared to manual measurement of erosion pins. A study of sand movement in a dune complex on the southeastern shoreline of Lake Michigan provides an example of the method’s application. Photoscale pin measurements that bracket a wind event associated with Hurricane Sandy show average surface elevation changes of 3.97 cm/pin. Regional wind data, pin measurements, and surface changes recorded in gigapixel panoramas suggest that vegetation baffling, recirculation eddies, and topographic steering played roles in sand deposition and erosion at the site. Photographic measurement of erosion pins can complement wind instrumentation and other tools as aeolian research increasingly incorporates multiple techniques to study surface changes in greater detail both in time and space.