Investigating the geomorphological potential of freely available and accessible structure-from-motion photogrammetry using a smartphone

We test the acquisition of high-resolution topographic and terrain data using hand-held smartphone technology, where the acquired images can be processed using technology freely available to the research community. This is achieved by evaluating the quality of digital terrain models (DTM) of a river bank and an Alpine alluvial fan generated with a fully automated, free-to-use, structure-from-motion package and a smartphone integrated camera (5 megapixels) with terrestrial laser scanning (TLS) data used to provide a benchmark. To evaluate this approach a 16.2-megapixel digital camera and an established, commercial, close-range and semi-automated software are also employed, and the product of the four combinations of the two types of cameras and software are compared. Results for the river bank survey demonstrate that centimetre-precision DTMs can be achieved at close range (10 m or less), using a smartphone camera and a fully automated package. Results improve to sub-centimetre precision with either higher-resolution images or by applying specific post-processing techniques to the smartphone DTMs. Application to an entire Alpine alluvial fan system shows the degradation of precision scales linearly with image scale, but that (i) the expected level of precision remains and (ii) difficulties in separating vegetation and sediment cover within the results are similar to those typically found when using other photo-based techniques and laser scanning systems.