LiDAR Analysis
LiDAR – Hillshade Analysis
LiDAR (Light Detection and Ranging) is a remote imaging technology that uses laser light sent from equipment typically mounted on an aircraft. The laser light that is fired is bounced off a surface and then detected by sensors. The time elapsed between the light being sent and its return, along with intensity and angles of defraction, can be used to build up a highly accurate three-dimensional image of the surface being studied. The data generated can be processed as a Digital Surface Models (DSM), which contains all data collected, or a Digital Terrain Models (DTM) that artificially removes trees and buildings from the surface model.
DTM LiDAR data can be further processed using a number of techniques, including Hillshade Analysis. This is a process carried out by applying an algorithm in a GIS programme that subjects the DTM to an artificial light source. The DTM contains three dimensional information relating to the topography of a surface allowing for the generation of artificial shadows that can show up surface detail hard to detect on the ground or though other imaging methods. These shadows can be generated from any altitude angle (height), or any degree point on an imaginary compass (with 0° pointing north) – azimuth angle. The process is similar in many respects to the analogue technique of using raking or low angled light on a surface in order to reveal subtle details hard to detect in normal lighting conditions. LiDAR DTM data has the added advantages of negating most foliage cover, being highly accurate, and the ability to have features artificially enhanced or exaggerated in order to reveal very subtle differences in surface topography. Cartographic features such as contour lines and pseudo-colour can be added to enhance reading of the images.
Below are a number of DTM LiDAR samples that have been processed using Hillshade Analysis with various light sources and pseudo-colour renderings applied. They are presented as slide sets of eight azimuth angles. They cover an area that includes parts of five townlands located just south of Naas town in County Kildare. Within the area imaged is a known ringfort (RMP: KD024-005—-) and a previously unrecorded earthwork discovered in 2021 using this method and this data. The rignfort also has features not noted on the RMP record that are clearly visible in the LiDAR imagery. There are a number of other features that could be archaeological significant.
A series of renderings with a light source at an altitude of 5° and eight slides at separate azimuth position. A spectral pseudo-colour has been applied.
A series of renderings with a light source at an altitude of 5° and eight slides at separate azimuth position. A spectral pseudo-colour has been applied.
A series of renderings with a light source at an altitude of 45° and eight slides at separate azimuth positions using a pseudo-colour blue to yellow.
