Visualization techniques for an airborne laser scanning‐derived digital terrain model in forested steep terrain: Detecting archaeological remains in the subsurface

This paper presents the method used to efficiently identify and map previously unknown subsurface remains in a steep, forested, and mostly unexplored area, within the archaeological site of Porolissum, Romania. The remains are part of the defensive system of the ancient Roman Empire frontiers (Roman limes). The complementary use of high‐resolution airborne laser scanning derived digital terrain model and visualization techniques enabled the detection of 79 new, subsurface archaeological structures, most of which were confirmed by ground inspection to be key elements of the limes. The best performing methods, achieving detection of the maximum visible extent for over 75% of all features were in descending order: principal component analysis, simple local‐relief model, sky‐view factor, and positive openness. Analytical hill‐shading, slope, negative openness, and hill‐shading had a larger proportion of partial detections. The position of these ancient remains supports the hypothesis that this area was extensively deforested, for strategic purposes, during the Roman period. Employing one of the latest remote sensing techniques, we have identified the location of previously unknown, buried ancient structures of the Roman limes in Dacia Province, an essential step for compiling a database necessary for enlisting this Roman limes sector on the World Heritage List.