Accuracy Assessment of Point Clouds and DEMs Generated Using Millimetre Wave Radar

Abstract:

There is a pressing requirement for high spatial and temporal resolution measurements of natural terrain to improve our understanding of Earth system processes. Remote sensing technology offers various solutions to this problem each with their own strengths and weaknesses. In this study, we evaluate the accuracy of 3D point clouds and Digital Elevation Models (DEMs) generated using millimetre wave radar through a comparison with data collected from a coincident Terrestrial Laser Scanner (TLS) survey measuring the topography of a quarry. Millimetre wave radar offers a trade-off between high angular resolution imaging and the ability to continue sensing in poor weather conditions which defeat electro-optical instruments. Here we assess the performance of the AVTIS2 millimetre wave radar, a portable surveying instrument originally developed at the University of St Andrews for measuring the 3D shape of volcanic lava dome surfaces. AVTIS2 is a 94 GHz real-aperture, Frequency Modulated Continuous Wave (FMCW) radar with a range resolution of 0.75 m and a two-way beamwidth of 0.35° (i.e. a spot size of 6 m per km). Point clouds are derived from AVTIS2 measurements by calculating the distance to the maximum received power along each Line of Sight (LOS), from which DEMs are generated. In 2014, we deployed AVTIS2 and a commercial TLS instrument ~2 km from Balmullo Quarry in Scotland. The quarry is excavated from the side of a small hill and it presents steep bare rock faces interspersed by horizontal vehicle access benches. The higher point cloud densities of the TLS surveys are used as a validation data set to compare points clouds derived from the millimetre wave radar. We will report on the accuracy of AVTIS2 points generated using the range-to-maximum received power algorithm by assessing the location of points in a local area defined by the size of the radar beam footprint. Further, AVTIS2 point clouds are georeferenced by applying a coordinate transform which is calculated by measuring the range from the radar to a reference target whose position is precisely determined using GPS. The AVTIS2 georeferencing performance will be compared to the TLS point clouds. Overall, this study quantifies the accuracy of millimetre wave radar for mapping the 3D structure of environmental terrain.