What do the latest imaging systems in airborne objects reveal? Part 2

Archeological searching is being conducted from above at altitudes well below those of satellite orbits. One group of researchers has used an airborne laser scanner (ALS) mounted to a helicopter’s skid pad to reveal several cities between 900 and 1,400 years old beneath the tropical forest floor in Cambodia. The first LiDAR (light detection and ranging) survey was conducted in Cambodia in 2012. The remote-sensing LiDAR can pierce through the thick vegetation to give researchers critical information about what’s on the ground.

The LiDAR survey from a helicopter involves flying with pre-determined guidelines, including altitude, flight path and airspeed. In this four-dimensional space, the ALS pulses the terrain with more than 16 laser beams per square meter during flights. The elevation of each individual data point is determined by the time the laser pulse takes to return to the sensor. This time of flight sensing technique is commonly used in many earth-bound applications.

Data downloaded from the ALS is processed to create a 3D model of the measurements captured during the flights. Any sudden and radical changes in ground height are mapped out and technicians who have models of the terrain fine-tune the results to eliminate tree foliage and man-made obstacles from the data.

With the final 3D model available, archaeologists’ analysis can take months to process this information into useful maps. However, the helicopter-projected lasers have produced extremely detailed imagery of the Earth’s surface and help identify large numbers of mysterious geometric patterns formed from earthen embankments.