Evaluation of lidar and medium scale photogrammetry for detecting soft-cliff coastal change

Lidar and photogrammetry have both been evaluated for detecting short-term coastal change using the Black Ven mudslide, Dorset as a case study. A lidar-generated digital elevation model (DEM) was obtained and initially compared with a DEM generated using available 1:7500 scale aerial photography, and automated digital photogrammetry. The quality of these two data sets was assessed using a third DEM, derived using 6, total station and conventional ground survey methods. The vertical accuracies (rms error) of the lidar and photogrammetry were 0.26 m and 0.43 m respectively, although both data sets displayed a tendency to generate heights slighty lower than the elevation of the terrain surface. The quality of the two data sets was then assessed with respect to local slope angle. The accuracy of photogrammetrically, derived elevations varied with slope and more so than in the case of lidar. From these basic tests, lidar has proved to be more accurate than photogrammetry for soft-cliff monitoring. Further research is required to establish whether this trend is applicable to other data sets and specifically, for photogrammetric data acquired using larger scale imagery.