Publicações

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 – estados da Natureza, acções, consequências, perdas, risco, estratégia, admissibilidade, etc. Esta teoria, que pretende reproduzir o processo decisório racional, é ilustrada com um exemplo de aplicação muito simples: o dimensionamento do serviço de urgência de um hospital em função do afluxo médio esperado de doentes graves.

A tunnel has been under construction for the Lisbon Metro network on the muddy bed of river Tagus. An incident during the jet-grouting for the muddy soil treatment led to flooding of a specific sector of the tunnel and to the need for repair works. Consequently, a decision has been made to monitor with a short time resolution the movements of that sector before, during and after reparation works. This includes the 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, an automatic monitoring system has been designed and put in place, resorting to four LEICA TC2003 motorised total stations and to the available commercial software, LEICA GeoMoS. The computational procedure of the mentioned software implies a network configuration, in which every total station set up needs a cluster of control points associated with that particular setup in order to perform a space resection. However, it is often difficult to find stable points inside a tunnel under monitoring let alone during repair works. Therefore, to overcome this difficulty, adjustment software - EpochSuite – has been integrated into the monitoring system. Since it runs after the collection of data, the adjustment software makes it possible to perform a more robust and accurate computation of displacement vectors of signalised object points, which represent the tunnel under study. EpochSuite uses a database management approach that is particularly useful in handling many monitoring epochs and uses automatic outlier detection tools. This paper reports on the network configuration, the instrumental setup and the software framework in which the automatic monitoring system actually operates.

Like in other surveying works, UAV flights require prior work that involves flight planning and equipment preparation and, often, many complementary tasks. These may involve bringing together technicians from different domains, booking a car and possibly accommodation, and some time-consuming complementary bureaucratic work. Teams operating UAVs know how much the flights are affected by weather conditions. The wind is the weather variable that, in proportion (number of occurrences per year), causes the major number of changes to a scheduled work. Obtaining reliable information about the intensity of the wind, a few days in advance, is an asset for those who have to carry out the various tasks mentioned previously. There are several websites from which one can access weather forecasts. Is any website better because it presents more reliable data? The data and the analysis presented in the paper will give some clues. The data includes wind speed, registered daily, at 12:00 (pm) for a year, by a meteorological station with online data, which belongs to a meteorological institute. Also on a daily basis, several websites with meteorological data were consulted, and wind speed forecasts for the same hour for up to four days in advance were collected. An analysis of the data can provide information about whether there is a website that stands out for the quality of the forecasts, and if there is a need to consult several websites to have better information.

A measurement system based on GNSS (Global Navigation Satellite System) was installed at Cabril dam in order to monitor displacements at the top of the central section. The GNSS system consists of two receivers (stations), one located on the crest of the dam, in central section, and the second located on the left bank, on the top of a medium voltage pole of a line deactivated and cut to be about 6 m high, to work as reference station. Unfortunately, this GNSS monument is exposed to solar radiation and wind effects. Consequently, it is expected that these environmental factors could cause sub-daily noise in the estimation of the dam displacements due to the thermal tilts of the monument. This paper is concerned with the assessment of the impact of this GNSS monument on the noise in the continuous GNSS time series. In GNSS time series analysis, frequency-domain signature is obtained by converting time-domain data into its unique frequency components using a Fast Fourier Transform (FFT). Through the analysis of frequency-domain signal signatures, the dam displacement seasonal can be detected and isolated from the noise eventually caused by the GNSS monument instability.

Geometria das formas de fundo (altura e comprimento) com recurso a levantamento aéreo utilizando um UAV na lagoa de Albufeira

OSOM - SYSTEMATIC MONITORING OF MARITIME WORKS - is a monitoring programme developed by the Portuguese National Laboratory for Civil Engineering (LNEC) to support the decision-making process relative to the maintenance schedule, or even repairing time, of maritime works. The main goal of this programme is the monitoring of the structure’s behaviour, through the analysis of the data collected during monitoring campaigns performed by LNEC. In recent years, the programme has been enhanced with new functionalities, being one of the most important contributions the integration of photogrammetric surveys, with drones, to improve visual inspections. The stage of testing this new source of information has already been completed and, for this reason, drones and photogrammetric methods are fully incorporated in the now-called OSOM+ programme. Nevertheless, there is still place for new studies that will help, in the near future, to make the drone surveys more efficient. This paper presents an ongoing study and some conclusions that are emerging

An infrastructure of three corner reflectors for Sentinel-1 was deployed at the National Laboratory for Civil Engineering campus, in Lisbon, Portugal, with the collaboration of the IDL, FCUL. The infrastructure is formed by two triangular trihedral reflectors (1 x 1 m) and by a third one following a model proposed by the team. The third reflector is formed by two rectangular trihedrals with the vertical axis in common, each of the individual reflectors is oriented towards the ascending and the descending passes of Sentinel-1. Additionally, a Global Navigation Satellite System (GNSS) antenna is permanently installed on the reflector’s axis. This study presents the first precision assessment for displacements measured at the infrastructure using Persistent Scatterer Interferometry (PSI). The PSI processing was performed with SARPROZ software using 19 Sentinel-1A images acquired between October 2017 and May 2018. The reflectors’ displacements are being monitored through levelling and GNSS. Levelling is performed for all reflectors every two weeks. Nearby persistent scatterers are included in the levelling line. A second permanent GNSS antenna is installed on a building roof in the campus to be used as a reference. PSI double-differences were compared to levelling and GNSS ones, projected onto the sensor line-of-sight. Precisions of 1.1 mm and 1.6 mm were achieved for the triangular trihedral reflectors, while 1.2 mm and 1.5 mm were obtained for the rectangular trihedral ones. However, during March 2018, strong winds have damaged the structure on which the rectangular trihedral reflectors are installed. If the evaluation is performed considering only the dates before the failure or only the dates after the damage was fixed, precisions of 0.7 mm and 0.8 mm are obtained. These results suggest submillimetre precision might be possible to achieve. Processing a larger time series of images acquired after the damage fix will be needed to confirm.

The “Project ELEVAR– Study of Vertical Structures with Robotized Aircrafts”, has as its main objective the development of an aircraft for the autonomous photogrammetric surveys of vertical surfaces, namely of dam walls, bridge, pillars, and facades of buildings and monuments. The photographs obtained will support the visual inspections carried out in the scope of monitoring and safety control of civil engineering works. The aircraft will navigate through stereoscopic cameras, sensors and dedicated algorithms that allow the autonomous positioning and three-dimensional reconstruction of the structures without the aid of GNSS systems in areas of poor signal coverage or where high precision is required. The photographic surveys will be carried out with a distinct, high-definition camera, aided by a system that allows to acquire images at the desired moment. The system is being developed by a consortium of three entities the company TEKEVER ASDS (leader), integrating the Institute of Systems and Robotics of Instituto Superior Técnico and the National Laboratory for Civil Engineering. This paper presents the project and the results achieved.

O projeto "ELEVAR – Estudo Localizado de Estruturas Verticais com Aeronaves Robotizadas", financiado pelo programa COMPETE, tem como objetivo principal o desenvolvimento de uma aeronave destinada à realização autónoma de levantamentos fotográficos de superfícies verticais, nomeadamente paramentos de barragens, pilares de pontes e fachadas de edifícios e de monumentos. As fotografias obtidas servirão de apoio às inspeções visuais realizadas no âmbito do acompanhamento e controlo de segurança das obras de engenharia civil. A navegação da aeronave será realizada através de câmaras estereoscópicas, sensores e algoritmos dedicados que permitem o posicionamento autónomo e reconstrução tridimensional das estruturas sem o auxílio de sistemas GNSS em zonas de fraca cobertura de sinal ou em que é necessária alta precisão. Os levantamentos fotográficos serão realizados com uma câmara distinta, de alta definição, auxiliada por um sistema que permite adquirir imagens no instante pretendido. O sistema está a ser desenvolvido por um consórcio liderado pela empresa TEKEVER ASDS, integrando o Instituto de Sistemas e Robótica do Instituto Superior Técnico e o Laboratório Nacional de Engenharia Civil. A presente comunicação destina-se a apresentar o projeto e os resultados alcançados nos primeiros 18 meses de atividade.

The team developed a bidirectional corner reflector (CR) with the goal of achieving displacements from Sentinel-1 ascending and descending passes for the same point. From those observations, vertical and horizontal displacements are being determined and their uncertainty is being assessed through comparison to levelling and GNSS measurements. The bidirectional CR is composed by two rectangular trihedrals with the vertical axis in common. A GNSS antenna is permanently installed on that axis and the base where the reflector is installed enables it to move along pre-defined directions. The reflector vertical displacements are also being monitored through levelling every two weeks. This CR is part of an infrastructure installed in LNEC, which also includes two individual triangular trihedral CRs. One of those is also installed on a movable base, in order to allow the comparison between CRs of different shapes. Two evaluations of the measurements’ uncertainty will be presented: one with all the CRs being static and another one with the CRs moving along the line-of-sight of the descending pass. Uncertainty assessment for displacements along other directions will be performed in the future.

During the design process of rubble mound breakwaters 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 displacements of the armour layer units. To detect and measure these displacements different methodologies were tested: photogrammetry and 3D scan. All the methods were used to produce point clouds. Some points on the model of the breakwater and its surroundings were coordinated by surveying methods and used to access the accuracy. This paper describes the methodologies used and the results achieved.

Odelouca is the second largest earth dam in Portugal and holds an important water reservoir. A displacement map for the slopes around the reservoir during the initial phase of the first filling was built using a multitemporal interferometric synthetic aperture radar (MTI) technique. A method based on cluster and time series analysis is proposed in order to find patterns on the obtained scatterers. The points are aggregated through a measure of the similarity between their displacement time series and form clusters, whose properties can then be evaluated. The analysis can be complemented by additional information for a better understanding of the influence on the ground of the storage of such a large amount of water. Three different patterns were identified on the data: stable scatterers, scatterers moving away from the sensor and scatterers moving towards it. A set of outliers was also detected. One of the clusters may contain points susceptible to landslide occurrence.

O calendário Gregoriano não é mais do que uma reforma do calendário Juliano, devido a Júlio César, que adaptou os formalismos romanos a uma antiga estrutura solar de origem egípcia. Este ensaio descreve a história do calendário Gregoriano 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.

O Simulador de Cenários Sísmicos, LNECloss, é uma ferramenta computacional que permite avaliar perdas em consequência de um cenário sísmico especificado [LESSLOSS, 2007]. Esta ferramenta automática compreende vários módulos, como sejam, a modelação da acção sísmica no substrato rochoso e à superfície, a avaliação dos danos no edificado e a avaliação das perdas económicas e humanas. O Simulador foi integrado como aplicação externa num Sistema de Informação Geográfica (SIG) [Sousa, 2006]. Foram identificadas algumas necessidades de desenvolvimento no Simulador, que compreendem, por um lado, o alargamento do seu domínio geográfico para além do território de Portugal Continental, nomeadamente para o Arquipélago dos Açores, que possui uma taxa de ocorrência de sismos muito elevada e, por outro, a sua disponibilização através da Web, com um carácter autónomo, ou seja, que não necessite de alguma plataforma de informação geográfica tendo no entanto as suas capacidades no que respeita ao mapeamento e à síntese gráfica e tabular dos efeitos de um cenário sísmico. De entre as características deste simulador WebSIG, saliente-se uma interface gráfica de fácil operação, permitindo a sua utilização por agentes da protecção civil, no que respeita ao planeamento e à gestão da emergência na eventualidade de ocorrência de um sismo.

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, num referencial 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 regularização de problemas inversos lineares mal colocados e a sua aplicação às redes altimétricas e planimétricas usadas na monitorização de deslocamentos de pontos notáveis de grandes barragens por métodos da Geodesia Aplicada. A metodologia é ilustrada por intermédio de três casos de estudo.

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

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

The work presents the theoretical definitions of the gamma, multi-gamma, digamma and trigamma functions as well as operational approximations to compute their values. A more precise alternative, due to Robert Windschitl, to the traditional approximation of the gamma function by the Stirling’s series, is reported. The work is completed with a study case, related to the geodetic monitoring of large dams, that illustrates the previous concepts and definitions.

O trabalho descreve os princípios da análise Bayesiana, usando como caso de estudo a amostra aleatória normal identicamente distribuída. Após um curto preâmbulo histórico, são resumidos, na Secção 2, os conceitos mais importantes da análise frequencista. Nas secções seguintes, são abordados os temas Bayesianos mais importantes, tais como a estimação, pontual e regional (Secção 5), e o teste de hipóteses sobre os parâmetros da distribuição da amostra (Secção 6). As distribuições anteriores de Laplace, Jeffreys e conjugada normal-gama invertida são apresentadas na Secção 4. O problema da 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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