Well designed Geographic Information Systems (GIS) are a very useful tool for the analysis of coa... more Well designed Geographic Information Systems (GIS) are a very useful tool for the analysis of coastal dynamics phenomena. Coastal monitoring involves large quantities of data from several types and sources, which converge to a better description of the coastal dynamic. In order to model coastal behaviour it is also necessary to perform a multi-temporal study. The heterogeneity of the data
The Lower Tagus Valley region (LTV), located in the western Iberian margin, is characterized by C... more The Lower Tagus Valley region (LTV), located in the western Iberian margin, is characterized by Cenozoic terrains corresponding to the sedimentary infill of an important subsidence basin. The presence of thick Pleistocene and Holocene deposits produce the conditions for different site effects. The values of Vs30 are widely used because they provide site classification according to several codes, including the European Eurocode 8 (EC8). This classification is used for structure design by the engineering community, and for soil ground motion estimation, by seismologists. It is also used to design shake maps, before or after an earthquake, that can be used by emergency response organizations, seismological and geophysical institutions, universities, the media and the general public. Direct measures of Vs30 (travel time average of the shear wave velocity over the top 30 meters), using active seismic methods, are very few and involve long time and expensive experiments if done at a regio...
Resumo: Está em curso, desde o início de 2011, um programa de amostragem de alta frequência em pr... more Resumo: Está em curso, desde o início de 2011, um programa de amostragem de alta frequência em praias representativas do troço litoral sob jurisdição da Administração da Região Hidrográfica do Tejo, no âmbito do projecto para a criação e implementação de um sistema de monitorização no litoral na área de jurisdição daquela entidade. A aquisição de dados inclui topografia, sedimentos, e registos fotográficos, elementos que permitirão analisar a evolução morfodinâmica daquele troço litoral à escala sazonal, anual e de longo-termo. O conjunto de dados geográficos originado será centralizado, gerido e disponibilizado através de uma plataforma Web SIG. A definição de valores de referência para indicadores de diagnóstico do estado das praias, nortearão a concepção de um programa de monitorização à escala regional que constituirá uma ferramenta de apoio ao nível do planeamento e gestão, que suportará técnica e cientificamente a tomada de decisão relativamente aos usos e ocupação da zona cos...
ABSTRACT Sea cliff evolution is dominated by the occurrence of mass movements of different types ... more ABSTRACT Sea cliff evolution is dominated by the occurrence of mass movements of different types and sizes, being a considerable source of natural hazard in coastal areas. Hazard assessment requires the use of substantially complete inventories of cliff failures occurred in the past, which are usually produced by multi-temporal aerial photo based studies, where photogrammetric methods still combine the advantages of high accuracy and the possibility of monitoring periods of time in excess of half a century. However, the study of low retreat rate cliffs still involves problems, because parts of the cliff top contour remain unchanged during the monitoring period and retreat is restricted to the places where cliff failures have occurred. This situation creates problems related with the inherent difficulties of a multi-temporal processing of aerial photos (different flight directions and scales, insufficient ground control for older photos and poor radiometric quality) and requires the use of refined photogrammetric approaches to prevent the generation of false mass movements, which cannot be included in the inventories. Because cliff retreat is discontinuous in space and time, better sampling of the process requires the widening of the monitoring time window, by use of older aerial photos, which involve further problems as unavailable camera calibration and photo distortions. To address these problems, the sea cliffs of Burgau-Lagos coast (Southwest Algarve, Portugal) were studied using digital photogrammetry methods, which involved several aerotriangulation steps, generation of pseudo-camera data for the older aerial photos, stereo plotting of the cliff top, ridges and toe and automatic generation of digital terrain models. Inconsistencies in the results were solved by systematic stereo photo interpretation, supported by oblique aerial photos. This study enabled the detection and characterization of 137 cliff failures that occurred between 1947 and 2007 along the 13 km long cliffs, causing the loss of 10,234 m2 of horizontal area at the cliffs top. The cliff failures identified correspond to planar slides (58%) mainly in Cretaceous alternating limestone and marls, toppling failures (17%) mainly in Miocene calcarenites, slumps (15%) in Plio-pleistocene silty sands that infill the karst in the Miocene rocks, and the remaining 10% correspond to complex movements, rockfalls and not determined cases. The space distribution of cliff failures is quite irregular but enables the objective separation of sub sections with homogeneous retreat behavior, for which were computed mean retreat rates varying within one order of magnitude from 5x10-3m/year in strong sandstones to 5x10-2m/year in Miocene calcarenites with frequent karst sinkholes filled with Plio-pleistocene silty sands, reflecting the strength variations of the rock masses that compose the cliffs. The maximum value of local retreat of the cliff top was up to 33m, with more frequent values in the range 2m to 6m. The relation between the magnitude expressed by the maximum local retreat and frequency follows an inverse power law for values higher than 2m with exponent of 1.8, close to the values recently proposed (Marques, 2008). The photogrammetric methods used in this study, and specially the strategies to obtain reliable information from old aerial photos, provided an accurate characterization of the cliffs evolution and supported a reliable compilation of a systematic inventory of cliff failures occurred in a 60 years period. These methods provided a confirmation and enhancement of a previous inventory made with simplified methods, providing a more detailed picture of the space and time distribution of cliff failures, but without changing substantially the general pattern of the studied phenomena. The use of these methods requires a considerable degree of expertise and resources and, for reliable compilation of an inventory data set, a final systematic checking of each cliff retreat event is still required. The specific topic of DDEM generation for reliable assessment of volumetric data is still in development and may provide a significant improvement of the outputs of these methods in the particular topic of low cliff retreat rate monitoring. Reference: Marques, F.M.S.F. (2008) Magnitude-frequency of sea cliff instabilities. Nat. Hazards Earth Syst. Sci., 8, 1161-1171.
Sea cliff retreat is mainly caused by the occurrence of slope mass movements of different types a... more Sea cliff retreat is mainly caused by the occurrence of slope mass movements of different types and dimensions, which are a significant constraint for human activities and a source of consider- able natural risk. With the increasing use of cliffy coastal areas in recent decades, mainly with urban areas and lei- sure resorts, this problem has growing importance in many
ABSTRACT Although traditional and web map producers strive to deliver up-to-date products and old... more ABSTRACT Although traditional and web map producers strive to deliver up-to-date products and old aerial photographs do not fit in their concept, other users are rather interested in old aerial images and in temporal series. In Portugal, aerial surveys for mapping purposes started by the late thirties of the twentieth century as documented by the oldest existing aerial photos collection in the archives of the IGEOE in Lisbon. Being the oldest visual witnesses of the country, the relevance of the information they contain is unquestionable. The objective of this project is the recovery of an important national aerial photographic heritage hibernating in analogue format in the archives. In a test block, strategies to recover radiometry and spatial orientation were developed and successfully tested in order to make the photos accessible and workable by the modern scientific community and by the general public. A photo-geographic database has also been organized and made available.
Skip to main content. EARSeL-logo, European Association of Remote Sensing Laboratories EARSeL ePr... more Skip to main content. EARSeL-logo, European Association of Remote Sensing Laboratories EARSeL eProceedings. Google Scholar. ...
The principal users of aerial photography have always been the military and mapping agencies. Aer... more The principal users of aerial photography have always been the military and mapping agencies. Aerial photographs were considered for several decades as a means to an end and were no longer interesting once the map was compiled. In the era of digital photogrammetry and internet the photograph itself became more important. Nevertheless, traditional and web map producers strive to deliver up-to-date products and old photographs just don't fit in the concept. Other users of aerial photos are found in the areas of geology, geography, history, and archaeology. These are rather interested in old aerial photographs and in series of aerial photos of a particular site or region. In Portugal, aerial surveys for mapping purposes might have started by the end of the thirties of the 20th century as documented by the oldest collection of vertical aerial photos existing in the archives of the Instituto Geográfico do Exército (IGeoE) in Lisbon. Being the oldest visual witnesses of the country, ...
Well designed Geographic Information Systems (GIS) are a very useful tool for the analysis of coa... more Well designed Geographic Information Systems (GIS) are a very useful tool for the analysis of coastal dynamics phenomena. Coastal monitoring involves large quantities of data from several types and sources, which converge to a better description of the coastal dynamic. In order to model coastal behaviour it is also necessary to perform a multi-temporal study. The heterogeneity of the data
The Lower Tagus Valley region (LTV), located in the western Iberian margin, is characterized by C... more The Lower Tagus Valley region (LTV), located in the western Iberian margin, is characterized by Cenozoic terrains corresponding to the sedimentary infill of an important subsidence basin. The presence of thick Pleistocene and Holocene deposits produce the conditions for different site effects. The values of Vs30 are widely used because they provide site classification according to several codes, including the European Eurocode 8 (EC8). This classification is used for structure design by the engineering community, and for soil ground motion estimation, by seismologists. It is also used to design shake maps, before or after an earthquake, that can be used by emergency response organizations, seismological and geophysical institutions, universities, the media and the general public. Direct measures of Vs30 (travel time average of the shear wave velocity over the top 30 meters), using active seismic methods, are very few and involve long time and expensive experiments if done at a regio...
Resumo: Está em curso, desde o início de 2011, um programa de amostragem de alta frequência em pr... more Resumo: Está em curso, desde o início de 2011, um programa de amostragem de alta frequência em praias representativas do troço litoral sob jurisdição da Administração da Região Hidrográfica do Tejo, no âmbito do projecto para a criação e implementação de um sistema de monitorização no litoral na área de jurisdição daquela entidade. A aquisição de dados inclui topografia, sedimentos, e registos fotográficos, elementos que permitirão analisar a evolução morfodinâmica daquele troço litoral à escala sazonal, anual e de longo-termo. O conjunto de dados geográficos originado será centralizado, gerido e disponibilizado através de uma plataforma Web SIG. A definição de valores de referência para indicadores de diagnóstico do estado das praias, nortearão a concepção de um programa de monitorização à escala regional que constituirá uma ferramenta de apoio ao nível do planeamento e gestão, que suportará técnica e cientificamente a tomada de decisão relativamente aos usos e ocupação da zona cos...
ABSTRACT Sea cliff evolution is dominated by the occurrence of mass movements of different types ... more ABSTRACT Sea cliff evolution is dominated by the occurrence of mass movements of different types and sizes, being a considerable source of natural hazard in coastal areas. Hazard assessment requires the use of substantially complete inventories of cliff failures occurred in the past, which are usually produced by multi-temporal aerial photo based studies, where photogrammetric methods still combine the advantages of high accuracy and the possibility of monitoring periods of time in excess of half a century. However, the study of low retreat rate cliffs still involves problems, because parts of the cliff top contour remain unchanged during the monitoring period and retreat is restricted to the places where cliff failures have occurred. This situation creates problems related with the inherent difficulties of a multi-temporal processing of aerial photos (different flight directions and scales, insufficient ground control for older photos and poor radiometric quality) and requires the use of refined photogrammetric approaches to prevent the generation of false mass movements, which cannot be included in the inventories. Because cliff retreat is discontinuous in space and time, better sampling of the process requires the widening of the monitoring time window, by use of older aerial photos, which involve further problems as unavailable camera calibration and photo distortions. To address these problems, the sea cliffs of Burgau-Lagos coast (Southwest Algarve, Portugal) were studied using digital photogrammetry methods, which involved several aerotriangulation steps, generation of pseudo-camera data for the older aerial photos, stereo plotting of the cliff top, ridges and toe and automatic generation of digital terrain models. Inconsistencies in the results were solved by systematic stereo photo interpretation, supported by oblique aerial photos. This study enabled the detection and characterization of 137 cliff failures that occurred between 1947 and 2007 along the 13 km long cliffs, causing the loss of 10,234 m2 of horizontal area at the cliffs top. The cliff failures identified correspond to planar slides (58%) mainly in Cretaceous alternating limestone and marls, toppling failures (17%) mainly in Miocene calcarenites, slumps (15%) in Plio-pleistocene silty sands that infill the karst in the Miocene rocks, and the remaining 10% correspond to complex movements, rockfalls and not determined cases. The space distribution of cliff failures is quite irregular but enables the objective separation of sub sections with homogeneous retreat behavior, for which were computed mean retreat rates varying within one order of magnitude from 5x10-3m/year in strong sandstones to 5x10-2m/year in Miocene calcarenites with frequent karst sinkholes filled with Plio-pleistocene silty sands, reflecting the strength variations of the rock masses that compose the cliffs. The maximum value of local retreat of the cliff top was up to 33m, with more frequent values in the range 2m to 6m. The relation between the magnitude expressed by the maximum local retreat and frequency follows an inverse power law for values higher than 2m with exponent of 1.8, close to the values recently proposed (Marques, 2008). The photogrammetric methods used in this study, and specially the strategies to obtain reliable information from old aerial photos, provided an accurate characterization of the cliffs evolution and supported a reliable compilation of a systematic inventory of cliff failures occurred in a 60 years period. These methods provided a confirmation and enhancement of a previous inventory made with simplified methods, providing a more detailed picture of the space and time distribution of cliff failures, but without changing substantially the general pattern of the studied phenomena. The use of these methods requires a considerable degree of expertise and resources and, for reliable compilation of an inventory data set, a final systematic checking of each cliff retreat event is still required. The specific topic of DDEM generation for reliable assessment of volumetric data is still in development and may provide a significant improvement of the outputs of these methods in the particular topic of low cliff retreat rate monitoring. Reference: Marques, F.M.S.F. (2008) Magnitude-frequency of sea cliff instabilities. Nat. Hazards Earth Syst. Sci., 8, 1161-1171.
Sea cliff retreat is mainly caused by the occurrence of slope mass movements of different types a... more Sea cliff retreat is mainly caused by the occurrence of slope mass movements of different types and dimensions, which are a significant constraint for human activities and a source of consider- able natural risk. With the increasing use of cliffy coastal areas in recent decades, mainly with urban areas and lei- sure resorts, this problem has growing importance in many
ABSTRACT Although traditional and web map producers strive to deliver up-to-date products and old... more ABSTRACT Although traditional and web map producers strive to deliver up-to-date products and old aerial photographs do not fit in their concept, other users are rather interested in old aerial images and in temporal series. In Portugal, aerial surveys for mapping purposes started by the late thirties of the twentieth century as documented by the oldest existing aerial photos collection in the archives of the IGEOE in Lisbon. Being the oldest visual witnesses of the country, the relevance of the information they contain is unquestionable. The objective of this project is the recovery of an important national aerial photographic heritage hibernating in analogue format in the archives. In a test block, strategies to recover radiometry and spatial orientation were developed and successfully tested in order to make the photos accessible and workable by the modern scientific community and by the general public. A photo-geographic database has also been organized and made available.
Skip to main content. EARSeL-logo, European Association of Remote Sensing Laboratories EARSeL ePr... more Skip to main content. EARSeL-logo, European Association of Remote Sensing Laboratories EARSeL eProceedings. Google Scholar. ...
The principal users of aerial photography have always been the military and mapping agencies. Aer... more The principal users of aerial photography have always been the military and mapping agencies. Aerial photographs were considered for several decades as a means to an end and were no longer interesting once the map was compiled. In the era of digital photogrammetry and internet the photograph itself became more important. Nevertheless, traditional and web map producers strive to deliver up-to-date products and old photographs just don't fit in the concept. Other users of aerial photos are found in the areas of geology, geography, history, and archaeology. These are rather interested in old aerial photographs and in series of aerial photos of a particular site or region. In Portugal, aerial surveys for mapping purposes might have started by the end of the thirties of the 20th century as documented by the oldest collection of vertical aerial photos existing in the archives of the Instituto Geográfico do Exército (IGeoE) in Lisbon. Being the oldest visual witnesses of the country, ...
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