## 4 Discussion and Conclusions
The image resolution used for initial tie point detection and 3D reconstruction played a large role in mitigating or inflating the error, with a ratio of 1:3 depending on the setting. The best results were obtained using \"High\" alignment accuracy, followed by \"Medium\" and \"Highest\", with the same order also observed in terms of the number of tie points retained. This suggests that the alignment accuracy setting is not fully representative of the tie point quality (e.g., density and precision). With our findings, we also suggest using RTK image positions (pair pre-selection) for speeding up image alignment, with two orders of magnitude improvement together with enhanced tie point quantity and quality. The final evaluation using four repeat surveys demonstrated a very good reproducibility of the complete workflow for DEM collection, shown by a large number of surface cells over hypothetical stable zones (\(\sim\)5870 m\({}^{2}\)) characterized by a range between repeat elevations below 3.5 cm and a standard deviation of 1.1 cm on average. Using the measurement workflow enabled characterizing the submeter beach topographic roughness, creating realistic maps of bedform arrangement at the beach scale, whose interpretation is eased further through the provision of very-high-resolution orthophotos (0.1 m). This small-scale topographic complexity (e.g., patches of ripples and megaripples) was found to be widespread and represented a large volume of sediment not represented in the DEMs with metric resolutions and, hence, not accounted for in typical beach surveys. Through pursuing surveys, follow-up studies will be looking at bedform classification and interpreting the spatial patterns observed and their temporal evolution in relation to driving hydrodynamic processes. For dynamic environments such as beaches, this study further exemplified that photogrammetry has the potential to help characterizing morphological changes across a wide range of spatial and temporal scales. Conceptualization, S.B. ; methodology, S.B. and J.A. ; software, S.B. and P.S. ; validation, S.B., P.S. and J.A. ; formal analysis, S.B. ; investigation, S.B. ; data curation, S.B. ; writing--original draft preparation, S.B. ; writing--review and editing, S.B., P.S. and J.A. ; visualization, S.B. ; funding acquisition, S.B. All authors have read and agreed to the published version of the manuscript. This research received funding from LTSER-France \"Zone Atelier Brest-Iroise\". The authors wish to thank LTSER-France \"Zone Atelier Brest-Iroise\" for financing data acquisition at La Palue field site, as well as [PERSON] and [PERSON] for help with RTK-GNSS measurements. Sillon de Talbert is a monitoring site of the French coastal observatory SNO-DYNAILT ([[https://www.dynalit.fr/](https://www.dynalit.fr/)]([https://www.dynalit.fr/](https://www.dynalit.fr/)), accessed on 6 March 2022). Four reviewers provided comments on the initial manuscript, whose help is gratefully acknowledged. The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript or in the decision to publish the results.