ENVIRONMENTAL CHALLENGES, TECHNICAL SOLUTIONS AND STANDARD OPERATING PROCEDURES FOR DATA COLLECTION IN PHOTOGRAMMETRIC STUDIES TOWARD A UNIFIED DATABASE OF OBJECTS AND FEATURES IN UNDERWATER CAVES IN MEXICO
Keywords: Photogrammetry, underwater, caves, field methods, Mexico
Abstract. Mexico’s Yucatan Peninsula is predominantly formed as a karstic terrain on limestone substrates where hundreds of kilometres of now submerged caves constitute extended networks of galleries partially accessible through cenotes, or karstic windows. These cenotes and underwater caves contain numerous objects of great biological, historical, cultural and/or paleontological significance: human and animal remains, ancient Maya artifacts, ancient mines and traces of early human activities. Photogrammetric studies by technical divers allow researchers to access a vast array of data pertaining to objects or features which would otherwise remain inaccessible. However, the harshness of the study environment poses technical acquisition challenges which must be specifically addressed. This paper introduces these environmental challenges, including the geological properties of local caves, bottom composition, ceiling percolation and topography, as well as the intrinsic difficulties linked to the absence of light and the limited time available in an underwater work setting. Technical acquisition solutions, setups and standard operating procedures are then proposed to overcome these challenges. A further consideration is added pertaining to the overall goal of creating a global database for the study objects, thus requiring a unified format for all data: unique identifier, geolocation, minimum resolution, and the like. The authors, focusing on the fieldwork and the data-collection aspect of the photogrammetric study, rather than the data processing and metrological steps, define a new image acquisition methodology built around a compact and replicable setup which will allow the documenting of objects previously out of reach of traditional setups.