Toward Practical Imaging of Very Shallow Submerged Heritage: Evaluating Consumer-Grade Photogrammetry under Controlled Conditions

The documentation of submerged heritage in very shallow water presents a distinct operational challenge, particularly in contexts where rapid, low-cost, and non-intrusive recording is required. Consumer-grade imaging systems are increasingly used for exploratory survey, educational fieldwork, and preliminary documentation, yet their performance limits in shallow refractive environments remain insufficiently understood. This study evaluates the practical suitability of consumer-grade photogrammetry for very shallow submerged heritage imaging through a controlled cross-environment experimental design comparing image-based reconstructions acquired in air and shallow water under standardized acquisition geometry. Relative geometric behaviour was assessed using cloud-to-cloud comparison, surface consistency observations, and reconstruction completeness across a series of experiments involving different depths, objects, and imaging devices. The results show that reconstruction reliability decreases as shallow-water depth and optical complexity increase, with refractive effects, illumination variability, and limited stabilization contributing to localized distortion and reduced alignment robustness. The findings also indicate that improvements in visual image quality do not necessarily correspond to improved geometric performance. Rather than proposing a new photogrammetric model, the study provides an applied evaluation of the operational limits of accessible imaging systems in very shallow underwater contexts. Based on these observations, the paper outlines preliminary practical guidance for the use of consumer-grade photogrammetry in the documentation of very shallow submerged heritage.