http://repositorio.lnec.pt:8080/jspui/handle/123456789/1007761 Mon, 26 Oct 2026 10:07:16 GMT 2026-10-26T10:07:16Z http://repositorio.lnec.pt:8080/jspui/handle/123456789/1019141 Improvement of InSAR displacements based on GNSS station calibration over corner reflector Diaz, A.; Roque, D.; Lima, J. N.; Rodríguez, J.; Solla, M. This article presents an analysis of the effectiveness of performing a calibration through Global Navigation Satellite System (GNSS) data on different approaches of the Interferometric Synthetic Aperture Radar (InSAR). InSAR has become a key technique for monitoring ground surface, but its results often exhibit systematic biases and deviations from ground truth measurements. This study addresses the need for more reliable displacement data by evaluating a GNSS-based calibration approach across three InSAR processing approaches: i) Persistent Scattering Interferometry (PSI) method using the open-source software StaMPS, ii) PSI method using the commercial SARPROZ software and iii) the Quasi-PS method implemented with SARPROZ. Sentinel-1 A/B data from both ascending and descending orbits, covering the period from October 2017 to January 2019, were used. Displacement errors from the same points were modeled using polynomial regressions and calibrated using reference data from GNSS and levelling, both with submillimeter precision. The effectiveness of the calibration was assessed at two levels: locally (via a corner reflector) and globally (via a GNSS baseline several kilometers long). Results show that 25 out of 27 displacement time series required correction in the mean value, with StaMPS showing the greatest need for calibration. The calibration improved the original results at all scales and acted mainly on the mean difference, with linear calibration being the most robust and consistent option. These findings highlight the importance of incorporating ground truth data to enhance InSAR reliability and support its application in geodetic and structural monitoring. Mon, 01 Sep 2025 00:00:00 GMT http://repositorio.lnec.pt:8080/jspui/handle/123456789/1019141 2025-09-01T00:00:00Z http://repositorio.lnec.pt:8080/jspui/handle/123456789/1018817 Drone survey of an embankment dam to detect surface changes Henriques, M. J.; Silva, H. A point cloud is a set of three-dimensional coordinates, to which color (that of the object's surface) can be added. It's a simple way to reproduce this object (which could be a dam, a building, a breakwater, a street, a room) on the computer. The point cloud can be obtained by laser scanner survey, photogrammetric survey and, in the case of small objects, also by 3D scanning. The coordinates resulting from laser scanners and photogrammetric surveys are generally obtained with less accuracy than those obtained by classical methods developed within the scope of geodesy and surveying (topography). For this reason, the use of point clouds (and the 3D models created from these) in dams to detect changes, for example for safety control studies, is more suitable to embankment dams as these are works where there is a requirement for slightly lower accuracy of results, on the order of few centimetres. Despite being less precise coordination methods, the laser scanner and photogrammetric methods have a very important advantage in earthworks as they cover the entire surface with a cloud with a high density of points. A localized problem can be easily detected if it has an expression on the surface of the work. As part of a study aimed at obtaining better knowledge of some details of an embankment dam situated in Portugal, two aerial photogrammetric surveys were carried out, approximately one year apart, with a drone. From these surveys point clouds and 3D models of the dam's surface were created. The communication presents various aspects of the surveys as well as the clouds and models generated. Tue, 01 Apr 2025 00:00:00 GMT http://repositorio.lnec.pt:8080/jspui/handle/123456789/1018817 2025-04-01T00:00:00Z http://repositorio.lnec.pt:8080/jspui/handle/123456789/1018816 A 3D point cloud model of Santa Luzia dam and its contribution for improving the finite element mesh Henriques, M. J.; Dias, I. M.; Roque, D.; Gomes, A. The analysis and interpretation of the structural behavior of concrete dams is usually performed by using finite element models of the dam and its rock mass foundation. The finite element mesh of the dam must accurately represent the real geometry of the structure being traditionally created from the design drawings. Currently, techniques from geospatial sciences (laser scanning and photogrammetry) allow the creation of very rigorous 3D models of objects, based on point clouds of surfaces. The improved knowledge of dam geometry can be useful for creating more realistic meshes of the structure, thus increasing the accuracy of the numerical modeling. The paper presents a use case of data generated from a drone photogrammetric survey of a concrete arch dam. The Santa Luzia dam is the first arch dam built in Portugal (it was completed in 1943). The concrete of this dam is subject to a deterioration process due to expansive reactions of internal origin. A very comprehensive study of the structure was recently carried out, which included the mapping of pathologies in the faces and crest of the dam and the analysis and interpretation of the dam behavior. The mapping of pathologies was carried out using digital image processing techniques, based on orthomosaics generated from photographs obtained from ground and aerial surveys, using photogrammetric software. When generating orthomosaics, point clouds were created which were used to obtain data on the dam's geometry and to improve the finite element mesh created many years ago, based on the dam design drawings. The paper includes a description of the aerial survey and the presentation of the most important phases for obtaining the dam geometry and for preparing the finite element mesh. Tue, 01 Apr 2025 00:00:00 GMT http://repositorio.lnec.pt:8080/jspui/handle/123456789/1018816 2025-04-01T00:00:00Z http://repositorio.lnec.pt:8080/jspui/handle/123456789/1018603 Identificação e registo do estado de conservação de azulejos através de imagens multiespetrais Roque, D.; Coutinho, M. L.; Henriques, M. J.; Santos Silva, A.; Morais Pereira, S. Desde pelo menos o século 15 que Portugal mantém a tradição de uso de revestimentos azulejares na sua arquitetura. Devido à especificidade estilística, quantidade e continuidade da sua aplicação no edificado, o azulejo é considerado um dos principais contributos portugueses para o património cultural mundial. A sua preservação, manutenção e restauro é assim de extrema importância sendo a utilização de novas ferramentas digitais uma oportunidade ainda a explorar para potenciar a salvaguarda deste rico património. A fotografia permite construir representações digitais de superfícies azulejadas, que constituem um registo do estado de conservação dos azulejos numa determinada época. Os métodos fotogramétricos possibilitam a inclusão de informação geométrica nessa representação, o que permite o mapeamento e quantificação das áreas degradadas. Adicionando algoritmos de processamento digital de imagens, a identificação e determinação das dimensões das patologias pode ser efetuada de forma automática. O registo gráfico digital de danos para azulejos é particularmente desafiante, não só devido às dificuldades em fotografar uma superfície vidrada, mas também pela variabilidade de cores e padrões representados, que tornam cada caso de estudo único. Neste estudo, pretende-se analisar o estado de conservação de uma superfície de azulejos para além da capacidade de observação do olho humano. Para tal, são captadas imagens com elevada resolução espetral e em frequências também fora do espetro do visível, que permitem obter informação adicional sobre os azulejos e o seu estado de conservação. As superfícies são analisadas com base em imagens multiespetrais, com captação de imagens em várias frequências do espetro eletromagnético, incluindo o infravermelho próximo e o ultravioleta. Esta estratégia permite o mapeamento de um leque alargado de anomalias típicas de superfícies azulejadas, tais como falhas de vidrado, fendas, áreas restauradas ou biocolonização. Os diferentes materiais que compõem a superfície dos azulejos e das áreas alteradas apresentam padrões de absorção e reflexão característicos em determinadas frequências do espetro eletromagnético, que permitem a sua identificação e delimitação através das imagens captadas nessas frequências. A integração dos dados recolhidos através dos diferentes tipos de imagens permite a construção de um registo gráfico de danos dos azulejos bastante completo e preciso, constituindo uma fonte de informação valiosa para os conservadores-restauradores e para a salvaguarda deste património. Tue, 01 Oct 2024 00:00:00 GMT http://repositorio.lnec.pt:8080/jspui/handle/123456789/1018603 2024-10-01T00:00:00Z