Publicações

Summary: A Bayesian estimator with informative prior distributions (a multi-normal and an inverted gamma distribution), adequate to displacement estimation at dam monitoring net-works, is presented. The hyper-parameters of the prior distributions are obtained by Bayesian empirical methods with non-informative priors. The performances of the Bayes estimator and the classical generalized lest squares estimator are compared using two measurements of the horizontal monitoring network of a concrete gravity dam: the Penha Garcia dam (Portugal). In order to test the robustness of the two estimators, gross errors are added to one of the measured horizontal directions: the Bayes estimator proves to be significantly more robust than the generalized least squares estimator.

Results from the application of Persistent Scatterers Interferometry in Lisbon Metropolitan Area revealed two previously unknown subsiding urban areas: one (Laranjeiras) is located in the center of Lisbon; another (Vialonga) is to be found toward the North, in an industrial region crossed by Lisbon's main highway and railway lines. The two subsiding sectors are bordered by sharp velocity gradients, and the subsidence pattern appears partially delimited by mapped geologic faults. Surface geology and urbanization alone are unable to explain the phenomena. In the Vialonga area, the historical record of water pore pressure shows a clear decline of the levels (up to 65 m in 27 years), providing evidence of over-exploitation of groundwater resources. Limited information from wells drilled inside and outside the subsidence area points to a spatial correlation between the subsidence and the water pressure levels, and suggests that faults could be acting as hydraulic barriers in the aquifer system. The surface subsidence detected is probably caused by compaction of a clay-rich Oligocene-aged aquitard, led by over-exploitation of adjacent aquifers. The same Oligocene aquitard layer is present in the Laranjeiras area, immediately bellow a multi-layered sand–clay–limestone Miocene aquifer, but further work is needed to diagnose the possibility of over-exploitation of groundwater here. In this work we were able to independently confirm the PSI results, by comparing autonomous PSI results processed for the same geographical areas, and by comparing PSI with leveling and continuous GPS derived subsidence velocities, whose close match provided further ground validation of the space-borne PSI technique.

ABSTRACT: Local engineering precision networks are currently used to monitor the displacements of large dams, with safety control purposes. These one, two or three-dimensional networks are local, be-cause they are tied to local reference frames, and they are precision networks, because they aim at millimetric, or even submillimetric, accuracy. The most important obstacles to such an accuracy are the instrumental and environmental systematic errors. The atmospheric refraction, which cau-ses curvature of the path of the electromagnetic waves and changes its propagation velocity, is the major source of systematic errors. Effective measurement quality control strategies are of utmost importance to guarantee the quality of the results (displacements). The paper presents a quality control strategy supported by random quadratic forms that result from the decomposition of the Mahalanobis squared norm of the residuals vector. The strategy is compared to the well known da-ta-snooping method with regard to the quality control and parameter estimation performances.

Apresentam-se, neste artigo, os conceitos da inferência paramétrica Bayesiana, no contexto da estimação dos parâmetros de amostras aleatórias normais. São abordados temas práticos não triviais, tais como as distribuições anteriores informativas e a sua eliciação paramétrica pelo método empírico. A finalizar o artigo, é apresentado um exemplo de aplicação da metodologia Bayesiana a um problema de estimação paramétrica no âmbito da engenharia de estruturas.

O presente trabalho introduz sumariamente os conceitos básicos da teoria da decisão estatística

A tunnel has been under construction for the Lisbon Metro network on the muddy bed of river Tagus. Anincident during the jet-grouting for the muddy soil treatment led to flooding of a specific sector of thetunnel and to the need for repair works. Consequently, a decision has been made to monitor with a shorttime resolution the movements of that sector before, during and after reparation works. This includesthe period in which the tunnel will be in use for its regular operation, with commuters using the subway.Given these general conditions with severe inter-visibility limitations, as well as the cost restraints, anautomatic monitoring system has been designed and put in place, resorting to four LEICA TC2003motorised total stations and to the available commercial software, LEICA GeoMoS. The computationalprocedure of the mentioned software implies a network configuration, in which every total station set upneeds a cluster of control points associated with that particular setup in order to perform a spaceresection. However, it is often difficult to find stable points inside a tunnel under monitoring let aloneduring repair works. Therefore, to overcome this difficulty, adjustment software - EpochSuite

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Atmospheric effects are still a limitation to the application of InSAR techniques for displacement measurement. In this study, zenith total delay (ZTD) values derived from global navigation satellite system (GNSS) are used to correct interferograms from tropospheric effects. Displacement measurements are obtained from the corrected interferograms through a persistent scatterer interferometry approach. The influence of different interpolation methods on the construction of ZTD maps is tested through two different algorithms: cubic spline and ordinary kriging. Differences are observed between the cumulative displacement maps obtained with both interpolators, but atmospheric effects are still present, possibly due to the small number of available GNSS stations.

A comunicação apresenta uma análise preditiva Bayesiana das medições de uma base

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MEO Arena building is one of the largest indoor arenas of the European Union and the largest one in Portugal. Due to its large capacity and unique structural characteristics, being composed of an inner wooden structure covered by a metallic roof, displacement measurements for structural health monitoring of the building is of utmost importance. This paper presents a method for displacement analysis of its metallic roof based on displacements acquired through Persistent Scatterer Interferometry and on geodetic measurements of the inner wooden structure. Regression models are used to estimate geodetic measures for the time of the SAR observations. Displacements of the metallic roof show a high correlation with temperature.

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During the design process of a rubble mound breakwater, in order to evaluate its effectiveness, scale model tests are required to study the hydraulic and structural behaviour of the proposed structure under predefined sea-wave conditions. The main goal of such tests is to study the structure overtopping and infer on damage progression by quantifying movements and displacements of the armour layer units. Scale model tests results can be also used to calibrate numerical models.Scale models of rubble-mound breakwaters are built in wave flumes (two-dimensional models, 2D) or in wave basins (three-dimensional models, 3D), enabling to simulate sea-wave conditions to study wave-structure interaction. A wave characterization and simulation software package is used to reproduce the prototype wave conditions, namely the significant wave height as well as the associated wave period. This makes possible to generate different sea states and therefore to study the rubble-mound breakwater behaviour and to identify possible weak areas in the armour layer.In order to characterize the armour layer envelope, recent applications of photogrammetric surveys were used, making it a promising technique. This method makes use of orthomosaics and clouds of points created from the photogrammetric survey. In this paper the first conclusions from the use of this technique are presented. The results of this analysis are extended to in situ breakwaters monitoring campaigns.

Ground displacements are a key factor to assess the safety and serviceability of any structure. A cost-effective technology for regional displacement monitoring, considering both the structure and its neighbourhood, would enable anomaly identification at an early stage and prevention actions. The objective of this work is to evaluate the stability of a segment of the Lisbon regional outer circular (circular regional exterior de Lisboa - CREL) through displacement measurements on the road and its surroundings using persistent scatterers interferometry (PSI).Synthetic aperture radar interferometry is a technology that uses satellite images acquired in the microwave band of the electromagnetic spectrum. PSI is one of the most used techniques, which allows measuring displacements at the Earth surface with millimetre accuracy. Man-made structures usually have stable reflective properties to microwaves, which turn them into good targets for displacement measurement through this technique. Therefore, it is possible to obtain a high density of measurements in urban areas.CREL is one of the most used roads to access Lisbon. The road has a length of 35 km and is fully operational since 1995. A displacement analysis using PSI was performed over an area of 50 km2, centred at Caneças (Odivelas municipality), which contains 8 km of CREL. Displacement measurements were computed for 1340 points/km2, every 11 days, between December 2011 and July 2013.Two areas close to CREL were identified presenting subsidence, with approximate areas of 0.6 km2 and 0.2 km2. Superimposed on this trend, an oscillatory behaviour was also detected.In conclusion, PSI is a useful technique to monitor displacements in urban areas and allowed the identification of possible unstable regions close to CREL, which may cause settlements at the road and damages at buildings nearby.

The protection of ports in coastal areas exposed to the action of the sea is carried by sea hydraulic structures (breakwaters) which are exposed to the influence of sea waves. The monitoring of the surface plates movement, constituting the protective mantle and the superstructure (concrete structure) is made by visual comparison of images obtained during follow-up visits. No quantification of these shifts is yet performed. In the design phase of a port protection structure, models are built to study the effect of waves on the protection blocks. During the testing phase waves are generated and periodically are measured the effects of waves in the model. Presently, photogrammetric monitoring of the model ports is being held, including the use of orthophotos and point clouds to measure displacements of protection blocks. With these methods there were obtained results of the change in overall topography of the model structure. However the real 3D motion of each block is indeterminate due to the absence of data on the geometry of the blocks. The extraction of thesegeometric data from the images, along with the spatial data of the point cloud, will deepen knowledge of the intended movement.This work presents an alternative monitoring solution based on image segmentation in order to obtain displacements of the model protection blocks so to monitor its development over time. Time sequence orthogonal images were obtained during the action of blocks movement. In this study, blocks are identified in the image and shifts are quantified. Validation is held by crossing image segmentation results with pointclouds data obtained in laboratory by photogrammetric methods at the same moment images were taken. The present study intends to show the positive contribution of image processing techniques for the laboratory monitoring of breakwater models.

Da utilização do GNSS em contínuo para monitorizar fenómenos geofísicos, nomeadamente a vigilância vulcânica, sísmica e tectónica, e as respostas dinâmicas e quase estáticas das grandes estruturas de engenharia civil resultam séries temporais que devem ser convenientemente filtradas em função do tipo de sinal (frequência e amplitude) que se pretende monitorizar. Com o GNSS e utilizando o mesmo tipo de equipamento, mas empregando modos de posicionamento diferentes, é possível monitorizar numa banda muito larga. Com efeito, o GNSS em modo estático relativo é mais adequado para vigilância de longo período porque este tipo de posicionamento caracteriza-se por detectar deslocamentos de baixa frequência com exactidão milimétrica. Por outro lado, para a monitorização de movimentos rápidos, deslocamentos de curto período e vibrações recorre-se a um posicionamento GNSS mais expedito, como o modo de posicionamento cinemático em tempo real ou o posicionamento cinemático pós-processado. Sendo estes últimos mais afectados pelos efeitos de multipath e, por essa razão, menos precisos do que o modo estático. A aplicação de filtros digitais permite melhorar a precisão do posicionamento GNSS pela mitigação do ruído das séries temporais. Nesta comunicação, aplicam-se dois filtros digitais, a média móvel simples e a média móvel exponencial, que são do tipo passa-baixo, a uma série temporal GNSS obtida duma base curta instalada no campus do LNEC.

O calendário Gregoriano não é mais do que uma reforma do calendárioJuliano, devido a Júlio César, que adaptou os formalismos romanos a uma antigaestrutura solar de origem egípcia. Este ensaio descreve a história do calendárioGregoriano e dos calendários da bacia do Mediterrâneo e do Oriente Próximo,com ele mais ou menos aparentados.

Interferometric synthetic aperture RADAR is an applied geodesy technique, which enables displacement measurement through satellite images. A literature review of the technique principles and of previous studies regarding its application to structural health monitoring allowed the identification of a few bottlenecks to the operational usage of this cost-effective technology for monitoring purposes.Three research lines were defined. First, a data mining strategy was developed to extract structural behaviour information from displacement time series from thousands of points on the region of interest, with tens of observation epochs each. Second, displacements from this technique were integrated into a previously existing monitoring system and were used to expand it to a larger number of points on the structure and to its surroundings. Third, an experimental infrastructure was deployed in order to perform several tests for displacement validation and uncertainty assessment. The infrastructure included a new model of artificial reflector to the satellite signals, purposefully developed in the scope of this study.The developed methods enabled the successful monitoring of different types of civil and geotechnical structures. Slope behaviour around water reservoirs was assessed during both the reservoir first impoundment and regular operation. Differential displacements were detected on building-blocks at a cultural heritage urban area and concrete arch dam responses to temperature loads were identified. The experimental work showed the achieved displacements agreed with those of other geodetic techniques and uncertainties around 2 mm were obtained for the measurements.In conclusion, interferometric synthetic aperture RADAR is a promising technique, able to provide useful information for structure monitoring, such as aiding in the planning of in situ monitoring activities and in identifying space-time patterns in structural behaviour. Thanks to its spatial coverage, observation period of a few days and achieved displacement uncertainty, it is advantageous to complement existing monitoring systems with data from this technique.

Neste relatório apresenta-se, de forma sucinta, a atividade de investigação realizada no âmbito do projeto ImEngine no período 2014-2023. Os resultados da atividade são analisados e avaliados, em face dos objetivos inicialmente previstos.

Neste relatório apresenta-se, de forma sucinta, a descrição da atividade de investigação realizada no âmbito do projeto INFRASAR no período 2014-2023. Os resultados da atividade são analisados e avaliados, em face dos objetivos inicialmente previstos.

Neste relatório apresenta-se, de forma sucinta, a descrição da atividade de investigação realizada no âmbito do projeto MEGA no período 2015-2023. Os resultados da atividade são analisados e avaliados, em face dos objetivos inicialmente previstos.

Este relatório apresenta os procedimentos do levantamento fotogramétrico, realizado com um drone, assim como as ações complementares, destinados a obter informação de carácter geométrico da praia da Cova Gala em 2020. Este documento inclui ainda uma análise da qualidade dos produtos gerados e uma comparação com o levantamento realizado em 2019, cerca de um ano antes.

Este relatório apresenta os resultados da campanha de nivelamento geométrico das bocas de furos de captação de água na proximidade da Base das Lajes, realizada pelo Núcleo de Geodesia Aplicada do Departamento de Barragens de Betão do LNEC, em outubro de 2020. Os resultados são as cotas, numreferencial local, das bocas dos furos de captação de água.

Este relatório apresenta os procedimentos dos levantamentos fotogramétricos, realizados com um drone, assim como as ações complementares, efetuadas em 2019, destinados a obter informação de carácter geométrico das praias de Cova - Gala, Vieira e São Pedro de Moel.

Neste relatório apresenta-se, de forma sucinta, a atividade de investigação realizada no âmbito do projeto ImEngine no período 2014-2017. Os resultados da atividade são analisados e avaliados, em face dos objetivos inicialmente previstos, sendo proposta uma extensão do projeto, e respetiva revisão do plano de atividades, para os próximos dois anos.

Neste relatório apresenta-se, de forma sucinta, a descrição da atividade de investigação realizada no âmbito do projeto INFRASAR no período 2014-2017. Os resultados da atividade são analisados e avaliados, em face dos objetivos inicialmente previstos, sendo proposta uma extensão do projeto e revisão do plano de atividades para os próximos dois anos.

Neste relatório apresenta-se, de forma sucinta, a descrição da atividade de investigação realizada no âmbito do projeto MEGA no triénio 2015-2017. Os resultados da atividade são analisados e avaliados, em face dos objetivos inicialmente previstos, sendo proposta uma revisão do plano de atividades para os próximos dois anos.

O relatório apresenta uma proposta de plano de estudos para a tese de doutoramento da bolseira Dora Roque, a realizar no Núcleo de Geodesia Aplicada do Departamento de Barragens de Betão do Laboratório Nacional de Engenharia Civil. O objetivo principal do estudo é contribuir para a operacionalização da geodesia InSAR na determinação de deslocamentos para o controlo de segurança de estruturas.

O trabalho aborda simultaneamente a distribuição do desvio padrão da amostra aleatória normal e a distribuição do desvio padrão do modelo de Gauss-Markov, designados genericamente por desvio padrão empírico. Após mostrar que o desvio padrão empírico é um estimador excêntrico que subestima o desvio padrão da amostra ou do modelo, conforme o caso, são apresentadas correções de excentricidade. É também tratada a estimação do desvio padrão da amostra e do modelo em cenário Bayesiano, com diferentes distribuições anteriores. O trabalho é rematado por casos de estudo baseados na simulação de amostras normais e por um exemplo concreto relacionado com o controlo da precisão de um distanciómetro eletromagnético.

O presente trabalho apresenta uma metodologia genérica para a regularizaçãode problemas inversos lineares mal colocados e a sua aplicação às redes altimétricas eplanimétricas usadas na monitorização de deslocamentos de pontos notáveis de grandesbarragens por métodos da Geodesia Aplicada. A metodologia é ilustrada por intermédiode três casos de estudo.

This paper deals with the beta-binomial model, which is an important stochasticmodel within the scope of the Bayesian statistical inference. After a short review of the binomialand beta distributions, the paper presents the closed formulae for the posterior probabilitydensity function of the binomial trial parameter and for the prior predictive and forthe posterior predictive probabilities of the successes in binomial experiments. A descriptionof the Bayesian methodology to test different hyper-parameters for the conjugate priorprobability density functions of the beta family is also presented. Finally, the beta-binomialmodel is illustrated with a study case related to the quality control of the geodetic observationof large dams.

O presente trabalho, além de uma revisão sintética da abordagem frequencista,trata da abordagem Bayesiana da análise de regressão linear multivariada. É apresentadauma compilação de procedimentos e fórmulas para a estimação dos coeficientes da regressão,sob três cenários de informação anterior. Finalmente, o trabalho ocupa-se dosproblemas da predição de respostas e da comparação de modelos de regressão.

The work presents the theoretical definitions of the gamma, multi-gamma, digammaand trigamma functions as well as operational approximations to compute their values.A more precise alternative, due to Robert Windschitl, to the traditional approximationof the gamma function by the Stirling

O trabalho descreve os princípios da análise Bayesiana, usando como caso deestudo a amostra aleatória normal identicamente distribuída. Após um curto preâmbulohistórico, são resumidos, na Secção 2, os conceitos mais importantes da análise frequencista.Nas secções seguintes, são abordados os temas Bayesianos mais importantes, taiscomo a estimação, pontual e regional (Secção 5), e o teste de hipóteses sobre osparâmetros da distribuição da amostra (Secção 6). As distribuições anteriores de Laplace,Jeffreys e conjugada normal-gama invertida são apresentadas na Secção 4. O problemada eliciação paramétrica das distribuições anteriores conjugadas é tratado na Secção 7.Palavras Chave: distribuições anteriores e posteriores, divergência de Kullback-Leibler,eliciação paramétrica, factor de Bayes, fórmula de Bayes, verosimilhança.

Este trabalho define uma estratégia, apoiada o mais possível nas disponibilidades do LNEC, para a calibragem dos distanciómetros electromagnéticos (DEM) usados pelo Núcleo de Geodesia Aplicada na observação geodésica de barragens.

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