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

Marcel Storch,Norbert De Lange,Thomas Jarmer,Mirjam Adam

doi:10.3390/s22010217

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 6 m/s were feasible. Regarding the flight altitude, we recommend an altitude of 50–75 m above ground. At higher flight altitudes of 100–120 m above ground, there is the risk that terrain characteristics smaller than 50 cm 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 2 m), 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.

Highlights

In order to achieve a scanning pattern as uniform as possible, the speed of the rotating mirror (LPS, lines per second) must be adjusted to the flight parameters altitude above ground and speed before each flight
Since there has been no systematic approach to the application of UAV-LiDAR in historical conflict landscapes, we propose in this context to differentiate between the following two groups of terrain anomalies: Types of (A) historical traces and remains that show vertical differences in height from their surroundings in the order of magnitude of decimeters to meters and are clearly identifiable even by on-site inspection
At (d) and (f), you can even see deadwood, which was apparently incorrectly classified as ground by the filter algorithms CSF and ATIN but was successfully removed by SMRF, which makes the terrain anomalies stand out better here (e)

Summary

Introduction

Remote sensing generally means gathering information about the characteristics of the landscape by measuring the reflected irradiance from above. Passive systems like multispectral or hyperspectral sensors measure the solar radiation reflected from the earth’s surface and objects and vegetation on the surface and are highly dependent on the weather and light conditions during data acquisition. These techniques cannot capture the geometry of the earth’s surface in vegetated areas because the vegetation canopy can prevent the irradiation from reaching the ground [6,7]

Objectives

Methods

Results

Discussion

Conclusion