WORKFRAME FOR CLOSE-RANGE PHOTOGRAMMETRY DOCUMENTATION OF AN 11KM LONG ARCHAEOLOGICAL EXCAVATION, AL AIN, UAE

Abstract

Over a six-month period from late January to early August 2021 the Historic Environment Department of the Department of Culture and Tourism (DCT) Abu Dhabi carried out archaeological monitoring along a 11.5km stretch of a project to renew the existing border fence between the United Arab Emirates and Oman within the oasis city of Al Ain.The scope and sequence of the construction project determined the excavation and recording methodology employed. The trench was roughly straight-sided, 3.5m wide by 3–4m deep and entailed machine excavation of more than a million cubic meters. Documentation of this trench, which proceeded at an average distance of 80m a day, has informed our understanding of the landscape, identified locations for future archaeological work and assisted our ongoing efforts to manage and protect the historic environment. The project produced new data on the development of the historic oasis landscape of Al Ain, a UNESCO World Heritage property. Some of the most significant features revealed include a monumental stone tomb from the Late Bronze Age (2000–1300 BCE), an extensive Iron Age (1200-300 BCE) cemetery, high-status tombs of Late Pre-Islamic date (300 BCE–300 CE) and more than 50 ancient aflāj or underground water channels of various dates and techniques of construction, along with extensive evidence for distinct phases of Iron Age agriculture.Photogrammetry recording sessions numbered nearly three hundred in total, together creating a series of consecutive overlapping 3D models from which ortho-rectified images in plan and section have been produced for each of the zones along the trench route.This paper discusses the recording practice and workframe as it evolved over the course of the project, and the challenges found during the data acquisition phase in terms of the construction environment, lighting, geometry, tools, time and team size. It presents the system used to manage the digital data archive needed to keep track of 288 recorded photogrammetry sessions, along with the related ground control points survey. The paper discusses the challenges and available solutions for rapid processing and delivery of geo-referenced 3D models and ortho-rectified images generated throughout the project. It concludes with some general remarks on the peculiarly linear challenge of presenting the results of an archaeological excavation 11.5km long and 3.5m wide in both digital and hard-copy formats.