Browsing by Author "Cordeiro, Miguel Alexandre Vaz"
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- Beach-VolumesPublication . Cordeiro, Miguel Alexandre Vaz; Fernandes, Rui Manuel da SilvaThe main objective of the research work described in this manuscript was to develop methods (hardware/software) for three-dimensional data acquisition in order to perform morphological analysis in sandy shore environments. This system, when concluded, intends to estimate the volumetric variations in beaches being eroded at high rates, directly contributing for studies focused on the protection of the coastline. This work is particularly focused on the development of software to estimate the 3D positions using a dedicated low-cost hardware device that was also developed in the framework of this project. Several methods have been used to study these phenomena, such as classical topography by surveying discrete points with the utilization of theodolites and/or total stations that are highly time-consuming. Other methods that start recently being used, like terrestrial or airborne LiDAR, are very costly and are not suitable to be used in many locations due to governmental requirements (like permits, environment, and security issues). Similar limitations also occur with Mobile Mapping Systems (MMS) with laser scanners that permit the survey when the vehicle is moving on the beach. In order to minimize the issues presented by the techniques described above, it was developed a simple, economic, ef cient and accurate system that can be used to study the erosion phenomena in coastal area. This system should allow one to acquire accurate GNSS positioning data on beaches, using a simple acquisition device in order to enable the creation of a three- -dimensional surface of the study area, which temporal variation can permit to quantify the erosion rates. This system is formed by an acquisition device, a GNSS receiver and antenna, and a Android Tablet/Smartphone that allows us to collect the antenna attitude from it’s internal orientation sensors. To collect information from the angles of the sensors, an Android application was developed. With the Tablet/Smartphone attitude angles, it is possible to correct the GNSS observations in order to obtain the vertical position - a dedicated C# application was developed with this objective. This corrections allows the creation of surfaces that accurately represent the terrains where the observations were conducted. In the future, using several observations at different times, it is possible to study the variations of sand volumes of the surveyed beaches and analyse the morphological variations. Some preliminary tests were performed concerning the creation of the surfaces, in order to evaluate the internal accuracy of the entire system. For this goal, we developed several scripts, using GMT (Generic Mapping Tools), that can also be used in the future to calculate the variations of the beach volume. In this respect, the results of some tests carried out to evaluate the accuracy of the developed technology are presented. In particular, by analysing the deviations with respect to a reference surface and by evaluating the sensitivity when measuring on an irregular surface.