Detection and Morphologic Analysis of Potential Below-Canopy Cave Openings in the Karst Landscape around the Maya Polity of Caracol using Airborne Lidar

Abstract

Locating caves can be difficult, as their entranceways are often obscured below vegetation. Recently, active remote-sensing technologies, in particular laser-based sensor systems (LiDARs), have demonstrated the ability to penetrate dense forest canopies to reveal the underlying ground topography. An airborne LiDAR system was used to generate a 1 m resolution, bare-earth digital elevation model (DEM) from an archaeologically-and speleologically-rich area of western Belize near the ancient Maya site of Caracol. Using a simple index to detect elevation gradients in the DEM, we identified depressions with at least a 10 m change within a circular area of no more than 25 m radius. Across 200 km 2 of the karst landscape, we located 61 depressions. Sixty of these had not been previously documented; the other was a cave opening known from a previous expedition. The morphologies of the depressions were characterized based on the LiDAR-derived DEM parameters, e.g., depth, opening area, and perimeter. We also investigated how the measurements change as a function of spatial resolution. Though there was a range of morphologies, most depressions were clustered around an average maximum depth of 21 m and average opening diameter of 15 m. Five depression sites in the general vicinity of the Caracol epicenter were visited; two of these were massive, with opening diameters of ,50 m, two could not be explored for lack of climbing gear, and one site was a cave opening into several chambers with speleothems and Maya artifacts. Though further investigation is warranted to determine the archaeological and geological significance of the remaining depressions, the general methodology represents an important advancement in cave detection.

Geospatial revolution and remote sensing LiDAR in Mesoamerican archaeology

“…5). Even small openings into the ground that represent underground storage units (called "chultuns") and looted burial chambers in structures are visible; a large number of caves similarly have been detected and ground-checked (49).…”

Ancient Maya Regional Settlement and Inter-Site Analysis: The 2013 West-Central Belize LiDAR Survey

“…The algorithm started by selecting some local low points assumed as sure hits on the ground, within a specified window size. The nominal ground classification parameters used for this project were: Window Size: 25.0 m; Max Terrain Angle: 89.0 degrees; Iteration Angle: 9.0 degrees; Iteration Distance: 1.4 m. Points identified as outliers because of their low elevation relative to neighboring points were retained, as the area is known to contain openings to caves, which are potentially of archaeological significance [22]. On average, 2.8 returns per sq m were classified as ground return, but that varied widely depending on the local density of vegetation.…”

Lidar Processing for Defining Sinkhole Characteristics under Dense Forest Cover: A Case Study in the Dinaric Mountains

“…Vegetation obstruction can significantly limit the information related to ground surface. Airborne laser scanning have proven in several studies to be able to penetrate dense forest canopies and display the underlying ground topography (Hofton et al, 2002;Kobler et al, 2007;Weishampel et al, 2011). Due to this unique characteristic, high-density airborne laser scanning data has been used for many applications which get added value from high-resolution topography of the bare ground plane.…”