|
EARSeL: 2nd Workshop on Remote Sensing of the Coastal Zone Porto, Portugal, 9-11 June 2005 |
SESSION COASTAL ZONE MANAGEMENT |
J. Pais-Barbosa, F. Veloso-Gomes, F. Taveira-Pinto
Faculty of Engineering of Porto University - FEUP, Hydraulics and Water Resources Institute - IHRH
Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
jlpb@fe.up.pt, vgomes@fe.up.pt, fpinto@fe.up.pt
The wave regime on the west Portuguese coastal zone is one of the most energetic worldwide. Here, the hydrodynamic forces are the main coastal modelling agent. The littoral drift acts mainly in the North-South direction although some singular events from the Southeast can be found due to wave refraction and diffraction (Pais-Barbosa et al., 2003).
Accurate knowledge of the morphology and morphodynamic characteristics as well as their correlation through time is therefore of great importance, not only to understand the erosion processes, but also to understand the movement of sediments and the action of currents.
The main goal of this work is to develop a tool capable of performing aerial image analysis, such as coastal forms, wave breaking zones i.a. The results of the analysis performed will be integrated and made available through a GIS database. With this approach, it will be possible to typify, classify and analyse physical aspects, and the evolution of the local coastal dynamic evolution, in a medium to long term, as well as the hydromorphologies and coastal forms resulting from the wave action.
The coastal area studied is located at the Aveiro Lagoon sand spits, in between the south of Cortegaça and the north of Mira urban settlements. This coastal stretch is mostly a low-lying coastal plain with sand dunes and beaches. It has a general orientation NNE-SSW, and here coastal forms are constantly changing because of the very high hydrodynamic forces acting on this stretch.
The data used in this study are diverse and in different formats (digital and hardcopy), with different Datum, scales and years.
The first step of this work was to store the available data. For this it was necessary to scan the images from 1996 and 2001 surveys, and georeference – using ArcInfo 7.2.1 – aerial images from several years. The scanning process of aerial photographs inevitably introduces sources of error that affect the subsequent use of the imagery. The georeferencing process was achieved using common points on the 1995 survey (orthoreferenced) and on the 1996 and 2001 photogrammetric surveys.
After this process, the development of a specific GIS tool to visualize and integrate several formats of data, in particular the data resulting from image analysis, was started. This tool is being programmed in Visual Basic 6.0, and MapObjects 2.3. In parallel, a tool using Matlab 7.0 - in particular its toolbox image processing – is also being developed to analyse the images stored in the GIS database. The former tool will enable to collect information about wave breaking zones, wave trains, coastal forms, i.a. After processing, the information is saved in a text file and then converted into a dbf format, being exported into the GIS database where overlay with the other data is done.
The preliminary results of this work indicate that this approach is satisfactory. These will be presented. Also, it is expected that improvements at the level of the software and of the algorithm analysis, will result in improvements of the results, and therefore on the conclusions to be drawn from this work.
Last Update: 2005-03-16