Comparison between methods for creating DEMs of physical models

Within physical modelling, it is often necessary to create DEMs (digital elevation models) when testing the stability of rock structures or the filter layers and scour protection around foundations and other marine structures. These DEMs are used to detect changes in the position of the structure or surrounding protective material. Several methods are available to create these models, yet no one technique has been selected as an industry standard. A comparison between three widely used methods – terrestrial laser scanner (TLS), combined laser scanner (CLS) and structure from motion (SfM) – are presented within this paper. The CLS in underwater mode gave low measurement errors and can be deployed without having to drain the facility but requires a traverser system. An area of approximately 7 m by 4 m can be measured in half an hour. The TLS can survey a much larger area in the same time, but requires the facility to be drained. SfM is cheapest method, but struggles to create a full shape and more care must be taken. The CLS in underwater mode has been chosen for use in scour studies in the Fast Flow Facility, with high volumes of water but a relatively limited area.