Structural monitoring of a breakwater using UAVs and photogrammetry

Abstract

The present project addresses a problem related to the erosion effects on a breakwater barrier due to waves which leads to its degradation and that may eventually lead to lack of functionality of the structure. In the present case, the breakwater acts as a physical barrier between the Atlantic Ocean and the cargo Harbour of Leixões, in Matosinhos, Portugal, justifying the needs of health monitoring of the barrier.To monitor this structure, with a length of roughly 700 m, the need of a fast data acquisition system led to the choice of imaging techniques which allow for a fast acquisition of a diversified data set. The images were acquired using a high-resolution camera attached to an unmanned aerial vehicle (UAV), enabling a faster and more automated procedure that leads to the systematization of the process, while being compatible with the difficult accessibility of the structure, which is surrounded by sea waves. Point clouds corresponding to the breakwater’s geometry were then obtained from the set of the UAV aerial images using photogrammetry.Two image acquisition and processing operations were performed three months apart in order to compare the point clouds acquired in the different instances and identify possible changes in the geometric configuration of the breakwater. By registering the two point clouds and computing the distance between them, it was possible to show that some movement within the structure occurred between the two points in time.