Systematic Approach for Remote Sensing of Historical Conflict Landscapes with UAV-Based Laserscanning

Abstract

In order to locate historical traces, drone-based Laserscanning has become increasingly popular in archaeological prospection and historical conflict landscapes research. The low resolution of aircraft-based Laserscanning is not suitable for small-scale detailed analysis so that high-resolution UAV-based LiDAR data are required. However, many of the existing studies lack a systematic approach to UAV-LiDAR data acquisition and point cloud filtering. We use this methodology to detect anthropogenic terrain anomalies. In this study, we systematically investigated different influencing factors on UAV-LiDAR data acquisition. The flight parameters speed and altitude above ground were systematically varied. In addition, different vegetation cover and seasonal acquisition times were compared, and we evaluated three different types of filter algorithms to separate ground from non-ground. It could be seen from our experiments that for the detection of subsurface anomalies in treeless open terrain, higher flight speeds like 6m/s were feasible. Regarding the flight altitude, we recommend an altitude of 50–75m above ground. At higher flight altitudes of 100–120m above ground, there is the risk that terrain characteristics smaller than 50cm will be missed. Areas covered with deciduous forest should only be surveyed during leaf-off season. In the presence of low-level vegetation (small bushes and shrubs with a height of up to 2m), it turned out that the morphological filter was the most suitable. In tree-covered areas with total absence of near ground vegetation, however, the choice of filter algorithm plays only a subordinate role, especially during winter where the resulting ground point densities have a percentage deviation of less than 6% from each other.

Point Density Variations in Airborne Lidar Point Clouds

“…While some authors include point density analysis [ 23 , 25 , 108 , 109 ] or take into account local density variations when processing lidar point clouds [ 87 , 103 , 110 , 111 , 112 , 113 , 114 , 115 ], our overview further highlights the importance of point density analysis as a starting point for studies using lidar point clouds. Special care should be given to point clouds used as input for analytical methods that are highly influenced by point cloud density, such as many vegetation-related metrics.…”

A High Gain Deployable L/S Band Conical Helix Antenna Integrated With Optical System for Earth Observation CubeSats

“…The width of the swath (S) available on the market in (many) optical cameras and multispectral imagers ranges from 5 to 195 km for height H=500 km [53,54]. With such parameters, the values of scan angle (α) lie in the range from 1° to 30°, which can be calculated using the following formula (3) [55]:…”

Detecting Historical Terrain Anomalies With UAV-LiDAR Data Using Spline-Approximation and Support Vector Machines

“…While this technology is already used in various environmental remote sensing studies [14]- [17], it is rarely used in the context of archaeological and cultural heritage applications [5], [18]. Its systematic use with respect to the UAV flight parameters for scanning historical terrain features in different types of vegetation was investigated [19]. In terms of achievable resolution, it should be noted that the absolute number of data points per square meter is significantly lower for ALS than for UAV-LiDAR.…”

“…In terms of achievable resolution, it should be noted that the absolute number of data points per square meter is significantly lower for ALS than for UAV-LiDAR. The latter can achieve point densities that are ten times higher than those of aircraft mounted laser systems [4], [19]. In addition, the laser footprint is much larger when using ALS (in the order of decimeters) than when conducting laser scans from a UAV (in the order of centimeters) [19].…”

“…The latter can achieve point densities that are ten times higher than those of aircraft mounted laser systems [4], [19]. In addition, the laser footprint is much larger when using ALS (in the order of decimeters) than when conducting laser scans from a UAV (in the order of centimeters) [19]. Of course, this is also a measure of how detailed the earth's surface and objects are captured by the system [20].…”