DETECTION AND QUANTIFICATION OF MORPHOLOGICAL CHANGES USING MULTI-RESOLUTION TERRESTRIAL LASER SCANS

Detection of changes is a key component for monitoring the dynamics of natural environments. Such detection is involved because of the complexity of such environments and the level of detail that is required in some cases. Answering the need for a detailed documentation of such changes in the surface morphology, a growing number of studies are making use of laser scanners, airborne and terrestrial, to detect and quantify them. For the change detection itself, many point-cloud processing based approaches interpolate the data and apply a pixel-based subtraction. Such analyses are 2.5D by nature and assume a change along fixed trend (mostly vertical) which does not reflect actual surface modifications in complex topographical settings. We propose in this paper a novel methodology for detection of changes in such environments. Our model involves no data loss, is three-dimensional, and requires no imposition of external constraints (e.g., enforcement of a positional constraint). Unique features of the proposed methodology lie in its ability to process point clouds with an unfixed scan resolution, and multiple scans from the same epoch. The proposed model is demonstrated on a site along the Mediterranean coastal cliff, a complex environment which undergoes rapid changes. The proposed model enables the detection of centimeter-scale changes as well as meter-size changes. These results serve as a basis for linking measured deformations with cliff-scale collapse mechanisms in order to gain a more comprehensive understanding of the cliff erosional processes and possibly identify collapse precursors such as crack widening and mass creep.