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Aplicação da Interferometria Radar no estudo de deslizamentos de terra na região de Lisboa
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O fenómeno geológico dos deslizamentos de terra provoca danos estruturais e perdas económicas podendo influenciar a economia de uma determinada região, causando por vezes vítimas mortais. Os danos provocados por este tipo de fenómeno geomorfológico estão muitas vezes relacionados com a intervenção humana, particularmente nas alterações efectuadas no meio ambiente provocando instabilidade no solo. Estes factos evidenciam a falta de um programa de avaliação do risco ligado à ocupação do solo. A avaliação do risco e da perigosidade de deslizamentos de terra à escala regional permite determinar os efeitos provocados pelos movimentos de massa, auxiliando na implementação dos planos de ordenamento do território ao nível municipal. Para tal, é fundamental adquirir informação sobre a deformação, normalmente obtida com recurso a técnicas geomorfológicas de campanhas de campo e reconhecimento de deslizamentos baseado em interpretação estereoscópica de fotografias aéreas, que são de elevado custo. O trabalho realizado nesta dissertação está inserido no projecto Metodologias de avaliação de perigosidade e risco de movimentos de vertente no âmbito dos Planos Municipais de Ordenamento e Território (MapRisk). O objectivo desta dissertação é a utilização da técnica da interferometria radar (InSAR), para avaliar as vantagens e desvantagens na detecção, monitorização e estudo de deslizamentos de terras. Partindo de um conjunto de imagens de satélite (SAR), que abrangem uma extensa área, é determinada uma série temporal de interferogramas que permite a construção de mapas de deformação regionais. Este produto resulta do processamento dos interferogramas num software muito particular (StaMPS), sendo composto por vários pontos denominados Persistent Scatterers (PS), onde vem representada uma medida de deformação de precisão milimétrica ao longo do período temporal de aquisição dos dados. A obtenção deste mapa e a sua implementação numa plataforma SIG, permite a detecção preliminar de zonas instáveis onde se pode estudar a susceptibilidade da ocorrência de deslizamentos de terra, sem os custos dos métodos tradicionais de trabalho de campo. Deste modo é possível criar um inventário de deslizamentos de terra baseado na interferometria radar, facilitando a elaboração de mapas de risco. A área de estudo compreende a região de Lisboa e vale do Tejo, tendo sido processados vários mapas de deformação para os períodos 1992-1997, 1998-2001, 1998-2005 e 2003-2005. Obteve-se uma grande densidade de pontos em áreas urbanas, permitindo detectar fenómenos de subsidência, e uma considerável densidade de pontos em áreas rurais, mais relacionados com deslizamentos de terra. Foi construído um MDT com 20 metros de resolução, para aplicação no processamento interferométrico. A obtenção de resultados coerentes em vários mapas de deformação de períodos distintos, demonstra fiabilidade nos dados obtidos por esta técnica. Obtivemos uma cadeia de processamento de mapas de deformação, aplicável a outras regiões captadas pelos dados SAR. Efectuou-se um estudo estatístico dos dados, permitindo separar as medições nos PS mais prováveis de representar deformação das medidas ruidosas influenciadas por descorrelação. Foi comprovado através de experiências no processamento, que a qualidade do mapa de deformação depende de vários factores. A construção óptima da série temporal de interferogramas é de importância vital para reduzir o ruído nos dados interferométricos, favorecendo o processamento e resultado dos PS.
The geologic phenomenon of the landslides causes structural damages and economic loses which can affect the economy of small communities, causing sometimes casualties. Damages related to this geomorphological phenomenon are often related to human activity, particularly in the modifications of the environment causing instability in the ground. This point out the lack of a program of evaluation of the land use risk. The evaluation of landslide risk and the hazard at regional scale allows the mitigation of the effects caused by these mass movements phenomena, providing support for implementation of territorial management programs at municipal level. For such, it is convenient to acquire information related to deformation. It is usually done by means of geomorphological surveys and recognition of landslides based on air photography interpretation. Both approaches are very expensive. The work carried through this dissertation is connected to the project Methodologies for assessing landslide hazard and risk applied to municipal planning (MapRisk). The main goal of this dissertation is the use of the radar interferometry (InSAR) technique to evaluate the advantages and disadvantages in the detection, monitoring and study of landslides. From a set of satellite images (SAR), that covers an extensive area, it is determined an interferogram time series that allow the construction of regional deformation maps. This product results from the processing of the interferogramas in a very particular software (StaMPS) and it’s formed by some points called Persistent Scatterers (PS), which represents a measure of deformation of millimetric precision throughout the time period of acquisition of the data. The implementation of the obtained map on a GIS platform, allows preliminary detention of unstable zones which permit to study the susceptibility of the occurrence of landslides, without the costs of the traditional surveys. This way it is possible to create a landslide inventory based on the radar interferometry, facilitating the elaboration of risk maps. The study area contains the region of Lisbon and vale do Tejo, and some deformation maps where processed for the periods 1992-1997, 1998-2001, 1998-2005 and 2003- 2005. We obtain a large density of points in urban areas, allowing detection of subsidence phenomena, and a considerable density of points in rural areas more related with land landslides. A DTM with resolution of 20 meters was processed for application in the interferometric processing. The attainment of coherent results in some deformation maps of distinct periods, demonstrates the reliability in the data obtain in the processing technique. We got a chain of processing of deformation maps applicable to other regions caught on SAR data. A statistical study has been done for this data, allowing to separate the measurements in the PS most probable to represent deformation from the noisy measures influenced by decorrelation. It was checked through experiences in the processing, that the quality of the deformation map depends on some crucial factors. The optimal construction of the time series is of vital importance for reducing the noise in the interferometric data, helping the processing and the result of the PS.
The geologic phenomenon of the landslides causes structural damages and economic loses which can affect the economy of small communities, causing sometimes casualties. Damages related to this geomorphological phenomenon are often related to human activity, particularly in the modifications of the environment causing instability in the ground. This point out the lack of a program of evaluation of the land use risk. The evaluation of landslide risk and the hazard at regional scale allows the mitigation of the effects caused by these mass movements phenomena, providing support for implementation of territorial management programs at municipal level. For such, it is convenient to acquire information related to deformation. It is usually done by means of geomorphological surveys and recognition of landslides based on air photography interpretation. Both approaches are very expensive. The work carried through this dissertation is connected to the project Methodologies for assessing landslide hazard and risk applied to municipal planning (MapRisk). The main goal of this dissertation is the use of the radar interferometry (InSAR) technique to evaluate the advantages and disadvantages in the detection, monitoring and study of landslides. From a set of satellite images (SAR), that covers an extensive area, it is determined an interferogram time series that allow the construction of regional deformation maps. This product results from the processing of the interferogramas in a very particular software (StaMPS) and it’s formed by some points called Persistent Scatterers (PS), which represents a measure of deformation of millimetric precision throughout the time period of acquisition of the data. The implementation of the obtained map on a GIS platform, allows preliminary detention of unstable zones which permit to study the susceptibility of the occurrence of landslides, without the costs of the traditional surveys. This way it is possible to create a landslide inventory based on the radar interferometry, facilitating the elaboration of risk maps. The study area contains the region of Lisbon and vale do Tejo, and some deformation maps where processed for the periods 1992-1997, 1998-2001, 1998-2005 and 2003- 2005. We obtain a large density of points in urban areas, allowing detection of subsidence phenomena, and a considerable density of points in rural areas more related with land landslides. A DTM with resolution of 20 meters was processed for application in the interferometric processing. The attainment of coherent results in some deformation maps of distinct periods, demonstrates the reliability in the data obtain in the processing technique. We got a chain of processing of deformation maps applicable to other regions caught on SAR data. A statistical study has been done for this data, allowing to separate the measurements in the PS most probable to represent deformation from the noisy measures influenced by decorrelation. It was checked through experiences in the processing, that the quality of the deformation map depends on some crucial factors. The optimal construction of the time series is of vital importance for reducing the noise in the interferometric data, helping the processing and the result of the PS.
Descrição
Tese de mestrado, Engenharia Geográfica, Universidade de Lisboa, Faculdade de Ciências, 2009
Palavras-chave
Interferometria Radar (InSAR) MapRisk Persistent Scatterer (PS) Deslizamentos de terra Deformação Lisboa Teses de mestrado - 2009