Joaquim Pais-Barbosa

Identification of beach hydromorphological patterns/forms through image classification techniques applied to remotely sensed data

The evaluation of beach hydromorphological behaviour and its classification is a complex issue. The main objective of this study was to develop new methodologies to identify coastal features/patterns. Pixel-based and object-oriented classification algorithms were used and a new approach was developed based on Principal Components Analysis and Histogram (PCAH) segmentation, to identify and analyse morphological features and hydrodynamic patterns. The PCAH method consists of three stages: preprocessing, PCA and histogram-based segmentation. Both manual and automatic approaches were addressed regarding the identification of the classes obtained from the segmentation stage. The dataset was composed from two aerial photographs and one IKONOS-2 image. The supervised classification algorithms present good results for both aerial photographs and the IKONOS-2 image. For the two aerial photographs the best results were found for the maximum likelihood classifier and for the IKONOS-2 image the best result was achieved with the parallelepiped classifier. The object-oriented classification performance for the aerial photographs and for the IKONOS-2 image also presented good results. The PCAH method led to promising results, with proportions of correctly classified pixels greater than 90% for the classes ‘Sea’, ‘Sediments+breaking zone’ and ‘Beach’.

Coastal Erosion Along the Portuguese Northwest Coast Due to Changing Sediment Discharges from Rivers and Climate Change

Coastal erosion is a common problem along sandy shores in Europe, a result of the dynamic nature of its coastal zones, of anthropogenic influences and of the effects of Climate Change. A possible increase of extreme events, the weakening of river sediment supplies due to dams and embankments and the expected acceleration of sea level rise tend to aggravate coastal erosion on decadal time scales. To minimize negative effects it is necessary to understand the various processes causing erosion so as to assess possible prediction scenarios for coastal evolution on the medium to long terms. This paper deals with the erosion situation to which the Portuguese northwest coast has been subjected, in relation to known sedimentary changes and to potential impacts of Climate Change on coastal areas. The possibility of re-using sediments from Portuguese reservoirs to nourish eroded beaches is pointed out. Also, coastal response to Climate Change driven variations in the longshore sediment transport regime is considered.

GIS Tool for Coastal Morphodynamics Analysis

The aim of this work is to identify morphological and hydrodynamic patterns (e.g. coastal forms, wave breaking zones, rip currents patterns, submerged bars), based on several aerial images. Understanding the patterns, which occurred in the past, may help to increase the knowledge to predict future ones. To accomplish this, a GIS database, an analysis algorithm and a user-friendly GIS tool are currently under development. The GIS database will enable to store all available image survey sets, as well as to store the results of the performed visual and computed analysis. This former analysis consists in a Matlab 7.0 algorithm, which uses mainly the toolbox image processing. For non GIS specialists, a specific tool to visualize, overlap and search is being developed using Visual Basic 6.0, and MapObjects 2.3.

Coastal morphodynamic features/patterns analisys through a video-based system and image processing

The Portuguese coastline, like many other worldwide coastlines, is often submitted to several types of extreme events resulting in erosion, thus, acquisition of high quality field measurements has become a common concern. The nearshore survey systems have been traditionally based on in situ measurements or in the use of satellite or aircraft mounted remote sensing systems. As an alternative, video-monitoring systems proved to be an economic and efficient way to collect useful and continuous data, and to document extreme events. In this context, is under development the project MoZCo (Advanced Methodologies and Techniques Development for Coastal Zone Monitoring), which intends to develop and implement monitoring techniques for the coastal zone based on a low cost video monitoring system. The pilot study area is Ofir beach (north of Portugal), a critical coastal area. In the beginning of this project (2010) a monitoring video station was developed, collecting snapshots and 10 minutes videos every hour. In order to process the data, several video image processing algorithms were implemented in Matlab®, allowing achieve the main video-monitoring system products, such as, the shoreline detection. An algorithm based on image processing techniques was developed, using the HSV color space, the idea is to select a study and a sample area, containing pixels associated with dry and wet regions, over which a thresholding and some morphological operators are applied. After comparing the results with manual digitalization, promising results were achieved despite the method’s simplicity, which is in continuous development in order to optimize the results.

Morphological Behaviour of Costa da Caparica Beaches Monitored during Nourishment Operations

ABSTRACT Silva, R., Veloso-Gomes, F. and Pais-Barbosa, J., 2013. Morphological Behaviour of Costa da Caparica Beaches Monitored during Nourishment Operations. Coastal erosion is a common problem along sandy shores in Europe, a result of its dynamic nature, anthropogenic influences and the effects of climate change. The coastal stretch Cova do Vapor-Costa da Caparica, located south from Tagus River, evidences chronic erosion problems since the 60s. It was necessary to construct a series of defence structures that more or less stabilized the beaches for nearly 30 years, although subjected to occasional overtopping and to increasing urban pressure and tourism. A worsening of the erosion situation from the winter of 2000/01 required a new intervention, which was envisaged in several phases, including the rehabilitation of the structures and the annual nourishment of the beaches. The nourishment operations were accompanied by a topo-hydrographic monitoring program, which complemented a database for the time period between 2001 and 2010. In this paper, the morphological behaviour of the sector is investigated making use of these data. A procedure for the analysis of its volumetric evolution is presented, following the test of different methods for volume variations estimation. Some conclusions about the behaviour of the sector and the lifetime of the nourishments are drawn, together with recommendations concerning topo-hydrographic monitoring. A morphological model and a medium to long-term coastline change model are being implemented at the site. Their implementation is intended to support the test, cost-effectiveness analysis and selection of interventions, for this site or others to which the analysis procedure may be exported.

Longshore Transport Estimation on Ofir Beach in Northwest Portugal: Sand-Tracer Experiment

AbstractThis work aims to shed some light on longshore sediment transport (LST) in the highly energetic northwest coast of Portugal. Data achieved through a sand-tracer experiment are compared with data obtained from the original and the new re-evaluated longshore sediment transport formulas (USACE Waterways Experiment Station’s Coastal Engineering and Research Center, Kamphuis, and Bayram bulk formulas) to assess their performance. The field experiment with dyed sand was held at Ofir Beach during one tidal cycle under medium wave-energy conditions. Local hydrodynamic conditions and beach topography were recorded. The tracer was driven southward in response to the local swell and wind- and wave-induced currents (Hsb=0.75m, Tp=11.5s, θb=8−12°). The LST was estimated by using a linear sediment transport flux approach. The obtained value (2.3×10−3m3⋅s−1) approached the estimation provided by the original Bayram formula (2.5×10−3m3⋅s−1). The other formulas overestimated the transport, but the estimations resu...

Coastal features analysis using GIS tools–stretch Esmoriz-Furadouro

The aim of this study is to identify morphological features and hydrodynamic patterns (e.g. coastal forms, wave breaking zones, rip current patterns, submerged bars), based on aerial photograph datasets. Understanding past patterns may help to increase the ability to predict future ones. To achieve the proposed objectives, a methodology to analyse aerial photograph datasets was developed. The analysis consists of visual identification of coastal features and patterns in a GIS environment. A GIS database was created to store the existing data and the result of the analysis. Several coastal features and patterns were identified, measured and correlated to the wave climate and other parameters. This correlation indicates that the presence and the dimensions of coastal features and patterns are closely related with the wave conditions and tide level, although the latter has less significance.

DGPS based methods to obtain beach cusp dimensions.

ABSTRACT Lopes, V., Baptista, P., Pais-Barbosa, J., Taveira-Pinto, F., Veloso-Gomes, F., 2013. DGPS based methods to obtain beach cusp dimensions. Statistical correlations between wave parameters and cusp dimensions other than spacing may provide insight into which processes intervene in beach cusps formation and evolution. However, there is little information about cusp dimensions such as cusp depth, height or elevation. The aim of this work is to evaluate and compare different methods to determine beach cusp dimensions in order to assess which one produces more accurate, extensive and easy-to-achieve results. For this purpose some beach surveys were carried out at Ofir beach, located on the Portuguese west coast. Each one of the methods uses different sampling and processing strategies to obtain beach cusp dimensions. In method 0 cusp dimensions were determined using only two tape measures. The remaining 4 methods use Differential Global Positioning System (DGPS). Methods 3 and 4 provide values for cusp spacing, height, elevation and depth whilst methods 1 and 2 provide values for the first three parameters only. If one is only interested in measuring beach cusp spacing, height and elevation, then method 1 seems to be more adequate, due to its ease in sampling and in dealing with the data processing. Values of spacing, height and elevation obtained via Method 1 are the most accurate ones. On the other hand, if one wishes to perform a more detailed analysis, including parameters other than the above-mentioned and, for instance, to produce Digital Elevation Models (DEM), a combination of Method 1 and Method 3 or 4 is more appropriate.

Quantitative and qualitative coastal water quality parameters monitoring using field data and aerial photography: Porto (Portugal) beaches

Under the scope of the Blue Flag project, a field campaign in order to collect water samples and a photogrammetric survey were performed at the urban seashore beaches of Porto, in August of 2008. Several water quality parameters were measured in different stations, following the European Directive 2006/7/CE. However, only 14 stations appear in the area covered by the aerial photographs. Multiple linear regressions were established in order to estimate the relationship between the DNs and three different water quality parameters (WQP). All the established models were found to be statistically significant and can be used to explain a considerable part of the data variability (R2>66%). A qualitative analysis was also performed in order to identify hydromorphologic features/patterns and correlate them with several WQP. The aerial photographs were classified in 6 classes (beach, beachface, breaking zone, rocks, sediments and sea). The maximum likelihood classifier presented the best performance. Analyzing the results in a GIS environment, it is clear that: for coliforms parameter the highest values appear near the mouth of urban small rivers (beach and beachface); for turbidity the highest values are located in the sediments class; and for the dissolve oxygen the highest values are located in areas with higher dynamics (breaking zone and beachface).

Bathymetric estimation through principal components analysis using IKONOS-2 data

The use of satellite remote sensing images could be a valid alternative to the classical methods of bathymetric measurements for depths less than 30 meters. In this work, several pixels corresponding to different depths are considered to numerically evaluate the relation between the water spectral response and the real depth, in the Douro River Estuary (Porto, Portugal). The main concept relies on principal components analysis, which allows for combining the information of the n available spectral bands from the image into an equal number n of principal components. The dataset is composed by an IKONOS-2 image and bathymetric values. An initial analysis was performed in order to determine the viability of the data for bathymetric study of the Douro River estuary. It was proved that it was not possible to find any direct relationship between the DNs of the IKONOS-2 image and depth values. Therefore, a simple linear regression of the bathymetric values on the IKONOS-2 image principal components was considered. A significant correlation was found between the first principal component and the real depths. In the future, the use of simultaneous data and the use of other statistical models such as decision trees may also provide important contributes to improve this methodology.