The Study: https://www.mdpi.com/2072-4292/18/20/3495

Walking the Blue Mountains west of Sydney is hard work. Sandstone cliffs, thick eucalyptus forest and deep valleys hide many rock shelters, and crews on foot miss a lot of them.

A University of Sydney team, working with the Dharug Custodian Aboriginal Corporation, tried a different approach. They used laser scans from the air plus a set of computer models to point the way. The study appears in Remote Sensing.

LiDAR fires laser pulses at the ground and times the return. Some pulses slip through gaps in the trees, so the data show the land under the canopy. The team tested two sources across a 1,057 square kilometer area. One was free, low-detail aircraft data from the New South Wales government, with at least 0.5 points per square meter.

The other came from a drone flown at 75 meters, which gathered at least 100 points per square meter over four zones. The models, built in ArcGIS Pro, look for steep slopes, big height gaps within a small patch of ground, and low terrain next to open space.

Shapes too small or too large get filtered out. The aircraft model produced 751,655 detections across the whole area. The drone model produced 2,017 in the four zones. The researchers checked the likeliest ones in 3D point clouds, then walked to them.

All 19 candidates they visited were shelters, overhangs or hollows under rock. The authors point out they picked those 19 by eye, so the number says nothing about overall accuracy. Results were stronger for known sites. Both datasets picked out six shelters already on record, including Honey Upgrade, Morley’s Creek and Emu Cave.

Coordinates in the state heritage database sat 1.78 to 30.10 meters from the drip lines the team mapped with a GNSS receiver. The LiDAR detections landed closer. The authors say some older records are off by hundreds of meters.

Three shelters had never been registered. BM139 holds three large stone artifacts on the floor. BM140 has 21 stone artifacts and a panel with two red hand stencils, one left and one right, covering about 35 by 15 centimeters. BM141 yielded 26 stone artifacts during a short surface check.

Time and money limit how many candidates a crew could visit, so the team ranks them. A drone detection within 1 meter of an aircraft detection gets high priority. A shelter named DJ1-028, which shows no visible artifacts, appeared only in the drone data. The aircraft data alone miss some shelters.

The study has gaps. The team has no false positive count and did not survey areas without detections. The settings were tuned for Blue Mountains sandstone, and the raster method struggles with deep undercuts. Work in other regions would need new calibration.

The Dharug asked the authors to leave out site coordinates and photos of rock art and stone tools, and they did. The team is still checking detections with the Dharug. Next, they plan to test the method in western Arnhem Land and western New South Wales.