Dr Rafael Carvalho1, Dr. David Kennedy2, Dr. Daniel Ierodiaconou1
1Deakin University, Warrnambool, Australia, 2The University of Melbourne, Melbourne, Australia
Historical aerial photographs are an invaluable tool in shoreline mapping and change detection in coastal landscapes. This study evaluates the extent to which Structure-from-Motion (SfM) methods can be applied to quantify volumetric changes along sandy beaches, using archival imagery. We demonstrate the application of SfM-derived Digital Surface Models (DSMs) at Apollo Bay, Marengo, Lady Bay and East Beach in southwest Victoria, using photographic datasets taken in 1946 onwards, and compared them to Light Detection and Ranging-derived DSMs acquired at all sites in 2007.
The SfM approaches resulted in several good DSMs of sub-metric quality and spatial resolution of less than 20 cm, reflecting different flight altitude and camera parameters for each individual model. The approach also generates seamless photomosaics, which can be used in traditional shoreline analysis, and allows detailed perspectives to investigate coastal processes based on unlimited defined angles and elevation views.
Volumetric change results demonstrated the consistency of the calculations for Apollo Bay, Marengo and Lady Bay with a less satisfactory result obtained for East Beach, despite the capacity of calculating erosion volumes to the east of the seawall from 1977 to 2007. Traditional shoreline analysis at all sites corroborate with patterns of volumetric accretion/erosion at these locations.
Based on results of these DSMs, several aspects of the use of SfM including strengths and weaknesses were highlighted. The use of SfM method to archival aerial imagery can potentially serve as benchmark for erosional studies not only in Victoria but throughout the world.
Dr. Rafael Carvalho is a Geographer with a research focus on coastal geomorphology and sedimentology, water resources and marine conservation. Rafael currently works as an Associate Research Fellow at Deakin University as part of the Victorian Coastal Monitoring Program team.