|M.Sc Student||Reuma Arav|
|Subject||Detection of Changes in Dynamic Geomorphological|
Environments Using Airborne and Terrestrial Laser
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Filin Sagi|
|Full Thesis text|
Advances in laser scanning technology enable acquisition of dense and accurate 3D terrain information. They are opening up new ways to investigate processes, detect and quantify changes, trace deformations, and monitor environmental changes. Nonetheless, characterization of changes to the surface morphology offers challenges due to the complexity of natural environments, the required level of detail, and the need to quantify abrupt as well as subtle changes. In this regard, this thesis studies methodologies for detection of changes in natural environments from both terrestrial and airborne laser scanning data. As for terrestrial scanners, the proposed model involves no data loss, is three-dimensional, and requires no imposition of external constraints. It is also capable processing point clouds with an unfixed scan resolution and multiple scans from the same epoch. Additionally, it reaches accurate detection, equivalent to the level of the scanner reported accuracy, while evaluating changes locally and not globally as most approaches do. As for the detection of changes between airborne acquired point clouds, it studies detection that documents changes on a larger scale while emphasizing reliability of the detection. In recognition of the limitations that such analysis has, a more elaborate analysis model is proposed for monitoring key geomorphic features, thereby offering documentation of changes on a larger and local scale.
The proposed model is demonstrated in two challenging environments, the first being a coastal cliff along the Mediterranean Sea, and the other along the receding Dead Sea coastal plains. Both feature complex environments which have undergone rapid and substantial changes. Along the coastal cliff, the proposed method traces the variations in all three-dimensions, thereby identifying changes that conventional methods have failed to detect. A centimeter-level of detection was reached using terrestrial scanners when applied on-site, while in a controlled environment a millimeter level of accuracy was reached. Such level of detection enables tracing the evolution of notches and terraces creation, and provide detailed understanding of the cliff erosional processes. Along the Dead-Sea coasts, where airborne laser data were acquired, the detection has managed tracing soil compaction, evolution of collapse sinkholes, and incision of channels. Incorporation of the global and detailed analyses facilitated the characterization and quantification of the processes that this region is undergoing. It also revealed inter-relations between the geomorphic features. Such analysis is vital for understanding the dynamics of these processes and for future development of the region.