The use of LiDAR is often mentioned as a way of locating information about places where missing children are buried.
This document outlines what LiDAR is, how it can be used in ground searches and GIS systems.
What is LiDAR?
Light Detection And Ranging is similar to RADAR but uses infrared light instead of radio waves. The principles for LiDAR, GPR, and RADAR are similar: an instrument sends out a signal, and the signal's reflection is recorded to reveal what it encountered. LiDAR is used to create 3D models of surfaces. New iPhones have LiDAR as an app that can make models of things. LiDAR is commonly used to map the surface of the land. It can create accurate models of the land to see the ground beneath plant cover. If burials or other historic features of interest have a surface shape, LiDAR can help find them, even in forests. LiDAR is commonly collected via drones.
What Role Can LiDAR Play in Identifying Missing Children?
The search for missing children is partly an exploration of landscapes from the past. Information on past landscapes can be found in historic maps, old air photos, and in survivor knowledge. However, some things from the past remain visible today as shapes on the ground surface. An old building, for example, may now be visible only by its foundation. Burials sometimes have surface shapes, usually slight mounds, or depressions. These are commonly seen in cemeteries. The burials of missing children may also have surface patterns. LiDAR can locate these burials, even if they are under vegetation or in forests.
LiDAR is collected in three ways: by airplane, by drone, and by a handheld device. Most ground searches for missing children will use drone LiDAR since it has the best quality detail of the surface shapes for the areas where burials of missing children are most likely to be. Handheld LIDAR might be useful in some places, but airplane LiDAR is not sensitive enough to find burials.
LiDAR works by sending out infrared beams and recording the reflections. The time and direction of the reflections allows us to build a model of the surfaces being scanned. LiDAR sends out millions of signals quickly, so the reflections can be filtered to remove the things that are near (like plants) and create a model of the things that are farthest away (like the ground surface). Models of the ground are usually put into a GIS for evaluation and comparison to other information.
What Are the Challenges of LiDAR Analysis?
LiDAR models of the ground from drones takes specialized equipment, software, and training. It is a useful tool for locating possible burials or cemeteries and for making accurate maps of landscapes of interest. It is fast to collect but requires specialized licensing to fly the drones and specific software and training to make the model and use it in a GIS. If there are no surface indication of graves, LiDAR cannot detect them and it does not look below the surface of the ground.
