Cost-effective non-metric close-range digital photogrammetry and its application to a study of coarse gravel river beds

Digital photogrammetry is now increasingly recognized as being a powerful tool in geomorphology. However, the high material costs and skills required by digital photogrammetry may deter non-photogrammetrists from using this technique in their research. This paper demonstrates the use of a close-range digital photogrammetric methodology accessible to non-photogrammetrists and yet capable of yielding good quality topographic information on coarse gravel riverbeds at minimal cost. Digital Elevation Models (DEMs) were derived from 1:165 scale imagery obtained with a 35 mm film SLR camera, a commercial desktop scanner and a softcopy photogrammetry package. Quality assessment based upon independent checkpoints and scaling analysis showed that the precision of the DEMs was consistently less than 10% of the D₅₀ of the bed particles. This translates into sub-centimetric precision. Whilst photogrammetry is presently capable of a better data quality at this scale, quality must be judged with respect to the requirements of the geomorphological applications under consideration. Thus, the methodological simplifications adopted in this research are acceptable in order to make photogrammetry both cost-effective and accessible.