Airborne Hyperspectral Imaging for Submerged Archaeological Mapping in Shallow Water Environments

Abstract

Nearshore areas around the world contain a wide variety of archeological structures, including prehistoric remains submerged by sea level rise during the Holocene glacial retreat. While natural processes, such as erosion, rising sea level, and exceptional climatic events have always threatened the integrity of this submerged cultural heritage, the importance of protecting them is becoming increasingly critical with the expanding effects of global climate change and human activities. Aerial archaeology, as a non-invasive technique, contributes greatly to documentation of archaeological remains. In an underwater context, the difficulty of crossing the water column to reach the bottom and its potential archaeological information usually requires active remote-sensing technologies such as airborne LiDAR bathymetry or ship-borne acoustic soundings. More recently, airborne hyperspectral passive sensors have shown potential for accessing water-bottom information in shallow water environments. While hyperspectral imagery has been assessed in terrestrial continental archaeological contexts, this study brings new perspectives for documenting submerged archaeological structures using airborne hyperspectral remote sensing. Airborne hyperspectral data were recorded in the Visible Near Infra-Red (VNIR) spectral range (400–1000 nm) over the submerged megalithic site of Er Lannic (Morbihan, France). The method used to process these data included (i) visualization of submerged anomalous features using a minimum noise fraction transform, (ii) automatic detection of these features using Isolation Forest and the Reed–Xiaoli detector and (iii) morphological and spectral analysis of archaeological structures from water-depth and water-bottom reflectance derived from the inversion of a radiative transfer model of the water column. The results, compared to archaeological reference data collected from in-situ archaeological surveys, showed for the first time the potential of airborne hyperspectral imagery for archaeological mapping in complex shallow water environments.

Combining Satellite Multispectral Imagery and Topographic Data for the Detection and Mapping of Fluvial Avulsion Processes in Lowland Areas

“…In order to identify Earth surface processes and associated landforms and, eventually, correlated archaeological and anthropic features, especially where political conflicts/warfare occur or the climate conditions prevent detailed fieldworks, the use of remote sensing techniques give a relevant support ( [23][24][25][26][27][28][29] and references therein). Moreover, wide extensions of the areas under investigation encourage the application of these techniques.…”

SfM photogrammetry for GeoArchaeology

“…In these studies, the intensity of LiDAR return is used to map wetter areas which normally correspond to deeper soils, fine and organic sediments and negative features. The most advanced scanning currently is the use of airborne multi and hyperspectral scanners which again can be used for crop marks (Aqdus et al, 2008), classical city plans (Cavalli et al, 2007) and even shallow marine features and survey (Guyot et al, 2019).…”

Classification of UAV point clouds by random forest machine learning algorithm

“…Multispectral LIDAR, which is a new remote sensing technology is able to measure both spectral and spatial information simultaneously and has proven to be usable method in various fields today (Chen et al 2017;de Almeida et al 2019;Wei et al 2012;Guyot et al 2019;Luo et al 2019;Niu et al 2015;Pan et al 2018). The first commercial aerial multispectral LiDAR, Optech Titan (532, 1,064 and 1,550 nm), has been brought new advantageous to the multispectral LiDAR land cover classification process (Wichmann et al 2015).…”